[1/4] dt-bindings: display: panel: document panel-id
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Message ID 20191207203553.286017-2-robdclark@gmail.com
State New
Headers show
Series
  • drm+dt: multi panel selection and yoga c630 display
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Commit Message

Rob Clark Dec. 7, 2019, 8:35 p.m. UTC
From: Rob Clark <robdclark@chromium.org>

For devices that have one of several possible panels installed, the
panel-id property gives firmware a generic way to locate and enable the
panel node corresponding to the installed panel.  Example of how to use
this property:

    ivo_panel {
        compatible = "ivo,m133nwf4-r0";
        panel-id = <0xc5>;
        status = "disabled";

        ports {
            port {
                ivo_panel_in_edp: endpoint {
                    remote-endpoint = <&sn65dsi86_out_ivo>;
                };
            };
        };
    };

    boe_panel {
        compatible = "boe,nv133fhm-n61";
        panel-id = <0xc4>;
        status = "disabled";

        ports {
            port {
                boe_panel_in_edp: endpoint {
                    remote-endpoint = <&sn65dsi86_out_boe>;
                };
            };
        };
    };

    sn65dsi86: bridge@2c {
        compatible = "ti,sn65dsi86";

        ports {
            #address-cells = <1>;
            #size-cells = <0>;

            port@0 {
                reg = <0>;
                sn65dsi86_in_a: endpoint {
                    remote-endpoint = <&dsi0_out>;
                };
            };

            port@1 {
                reg = <1>;

                sn65dsi86_out_boe: endpoint@c4 {
                    remote-endpoint = <&boe_panel_in_edp>;
                };

                sn65dsi86_out_ivo: endpoint@c5 {
                    remote-endpoint = <&ivo_panel_in_edp>;
                };
            };
        };
    };

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)

Comments

Sam Ravnborg Dec. 7, 2019, 9:13 p.m. UTC | #1
On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> For devices that have one of several possible panels installed, the
> panel-id property gives firmware a generic way to locate and enable the
> panel node corresponding to the installed panel.

For display timings there is something similar.
Here the property is named native-mode and is a phandle to the
preferred timing.
And it is documented that if no native-mode is specified the first
timing in the tree is chosen.  
So a different concept than this.

I could not from your otherwise well-documented changelog see why you
wanted to go for an opauge integer and status rather than a phandle to
the active display.

The panel-id, if I get it right, is optional and the important part is
that the first panel with staus = "okay" is selected.
This would cover my usecase fine.
I have a target with four different displays and the bootloader
knows what display is used (based on gpio etc).
The bootloader (barebox in my case) uses a simple variant of the DT,
but reads in the DT used by the kernel and can modify the DT before
it is passed to the kernel.

	Sam




> Example of how to use this property:
> 
>     ivo_panel {
>         compatible = "ivo,m133nwf4-r0";
>         panel-id = <0xc5>;
>         status = "disabled";
> 
>         ports {
>             port {
>                 ivo_panel_in_edp: endpoint {
>                     remote-endpoint = <&sn65dsi86_out_ivo>;
>                 };
>             };
>         };
>     };
> 
>     boe_panel {
>         compatible = "boe,nv133fhm-n61";
>         panel-id = <0xc4>;
>         status = "disabled";
> 
>         ports {
>             port {
>                 boe_panel_in_edp: endpoint {
>                     remote-endpoint = <&sn65dsi86_out_boe>;
>                 };
>             };
>         };
>     };
> 
>     sn65dsi86: bridge@2c {
>         compatible = "ti,sn65dsi86";
> 
>         ports {
>             #address-cells = <1>;
>             #size-cells = <0>;
> 
>             port@0 {
>                 reg = <0>;
>                 sn65dsi86_in_a: endpoint {
>                     remote-endpoint = <&dsi0_out>;
>                 };
>             };
> 
>             port@1 {
>                 reg = <1>;
> 
>                 sn65dsi86_out_boe: endpoint@c4 {
>                     remote-endpoint = <&boe_panel_in_edp>;
>                 };
> 
>                 sn65dsi86_out_ivo: endpoint@c5 {
>                     remote-endpoint = <&ivo_panel_in_edp>;
>                 };
>             };
>         };
>     };
> 
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> index ef8d8cdfcede..6113319b91dd 100644
> --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> @@ -75,6 +75,32 @@ properties:
>        in the device graph bindings defined in
>        Documentation/devicetree/bindings/graph.txt.
>  
> +  panel-id:
> +    description:
> +      To support the case where one of several different panels can be installed
> +      on a device, the panel-id property can be used by the firmware to identify
> +      which panel should have it's status changed to "ok".  This property is not
> +      used by the HLOS itself.
> +
> +      For a device with multiple potential panels, a node for each potential
> +      should be defined with status = "disabled", and an appropriate panel-id
> +      property.  The video data producer should be setup with endpoints going to
> +      each possible panel.  The firmware will find the dt node with a panel-id
> +      matching the actual panel installed, and change it's status to "ok".
> +
> +      The exact method the firmware uses to determine the panel-id of the installed
> +      panel is outside the scope of this binding, but a few examples are
> +
> +      1) u-boot module reading a value from a u-boot env var
> +      2) EFI driver module reading a value from an EFI variable
> +      3) device specific firmware reading some device specific GPIOs or
> +         e-fuse
> +
> +      The panel-id values are an opaque integer.  They can be sparse.  The only
> +      important thing is that each possible panel in the system has a unique
> +      panel-id, and that the values configured in the device's DTB match the
> +      values that the firmware is looking for.
> +
>    ddc-i2c-bus:
>      $ref: /schemas/types.yaml#/definitions/phandle
>      description:
> -- 
> 2.23.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
Rob Clark Dec. 7, 2019, 9:34 p.m. UTC | #2
On Sat, Dec 7, 2019 at 1:13 PM Sam Ravnborg <sam@ravnborg.org> wrote:
>
> On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> > From: Rob Clark <robdclark@chromium.org>
> >
> > For devices that have one of several possible panels installed, the
> > panel-id property gives firmware a generic way to locate and enable the
> > panel node corresponding to the installed panel.
>
> For display timings there is something similar.
> Here the property is named native-mode and is a phandle to the
> preferred timing.
> And it is documented that if no native-mode is specified the first
> timing in the tree is chosen.
> So a different concept than this.
>
> I could not from your otherwise well-documented changelog see why you
> wanted to go for an opauge integer and status rather than a phandle to
> the active display.

I think a lot of cases, panel-id could simply be an integer 0..N, but
for the snapdragon windows devices, they seem to assign each panel a
unique id.  For example, the two possible panels that we've seen on
the c630 are 0xc4 and 0xc5.  I think all the values we've seen so far
on other aarch64 laptops fit in an u8, but the actual value is defined
as u32.  The meaning behind those values is not really terribly
important (and might well be arbitrary.. I'm not sure why they didn't
go with a GUID).  All that matters is they match what DtbLoader pulls
out of the u32 PanelId field in the UEFIDisplayInfo variable.  The
intention behind describing the value as "opaque" was simply "don't
assume it has to be 0..N".

As far as using phandles, I had toyed around with the idea.. the ideal
thing would be if I could compile the dtb with an unresolved phandle
link, and then fixup that link in DtbLoader based on panel-id.  But
this seems not to be possible, afaict I'd have to create a dummy node
for the phandle to point to.  Maybe I'm missing something, if there
were a way to do this then I could make this work without any drm
patches.  Ofc I'm open to suggestions.

>
> The panel-id, if I get it right, is optional and the important part is
> that the first panel with staus = "okay" is selected.

yup, this was to ensure that the other panels don't probe, which was a
problem pointed out by robher with my previous approach

> This would cover my usecase fine.
> I have a target with four different displays and the bootloader
> knows what display is used (based on gpio etc).
> The bootloader (barebox in my case) uses a simple variant of the DT,
> but reads in the DT used by the kernel and can modify the DT before
> it is passed to the kernel.

I'd be pretty happy if this (or whatever the eventual solution is)
covers all the possible multi-sourced panel cases.. this comes up in
nearly all consumer devices (laptops, phones, etc) and we pretty badly
need an upstream solution for this.

BR,
-R


>
>         Sam
>
>
>
>
> > Example of how to use this property:
> >
> >     ivo_panel {
> >         compatible = "ivo,m133nwf4-r0";
> >         panel-id = <0xc5>;
> >         status = "disabled";
> >
> >         ports {
> >             port {
> >                 ivo_panel_in_edp: endpoint {
> >                     remote-endpoint = <&sn65dsi86_out_ivo>;
> >                 };
> >             };
> >         };
> >     };
> >
> >     boe_panel {
> >         compatible = "boe,nv133fhm-n61";
> >         panel-id = <0xc4>;
> >         status = "disabled";
> >
> >         ports {
> >             port {
> >                 boe_panel_in_edp: endpoint {
> >                     remote-endpoint = <&sn65dsi86_out_boe>;
> >                 };
> >             };
> >         };
> >     };
> >
> >     sn65dsi86: bridge@2c {
> >         compatible = "ti,sn65dsi86";
> >
> >         ports {
> >             #address-cells = <1>;
> >             #size-cells = <0>;
> >
> >             port@0 {
> >                 reg = <0>;
> >                 sn65dsi86_in_a: endpoint {
> >                     remote-endpoint = <&dsi0_out>;
> >                 };
> >             };
> >
> >             port@1 {
> >                 reg = <1>;
> >
> >                 sn65dsi86_out_boe: endpoint@c4 {
> >                     remote-endpoint = <&boe_panel_in_edp>;
> >                 };
> >
> >                 sn65dsi86_out_ivo: endpoint@c5 {
> >                     remote-endpoint = <&ivo_panel_in_edp>;
> >                 };
> >             };
> >         };
> >     };
> >
> > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > ---
> >  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > index ef8d8cdfcede..6113319b91dd 100644
> > --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > @@ -75,6 +75,32 @@ properties:
> >        in the device graph bindings defined in
> >        Documentation/devicetree/bindings/graph.txt.
> >
> > +  panel-id:
> > +    description:
> > +      To support the case where one of several different panels can be installed
> > +      on a device, the panel-id property can be used by the firmware to identify
> > +      which panel should have it's status changed to "ok".  This property is not
> > +      used by the HLOS itself.
> > +
> > +      For a device with multiple potential panels, a node for each potential
> > +      should be defined with status = "disabled", and an appropriate panel-id
> > +      property.  The video data producer should be setup with endpoints going to
> > +      each possible panel.  The firmware will find the dt node with a panel-id
> > +      matching the actual panel installed, and change it's status to "ok".
> > +
> > +      The exact method the firmware uses to determine the panel-id of the installed
> > +      panel is outside the scope of this binding, but a few examples are
> > +
> > +      1) u-boot module reading a value from a u-boot env var
> > +      2) EFI driver module reading a value from an EFI variable
> > +      3) device specific firmware reading some device specific GPIOs or
> > +         e-fuse
> > +
> > +      The panel-id values are an opaque integer.  They can be sparse.  The only
> > +      important thing is that each possible panel in the system has a unique
> > +      panel-id, and that the values configured in the device's DTB match the
> > +      values that the firmware is looking for.
> > +
> >    ddc-i2c-bus:
> >      $ref: /schemas/types.yaml#/definitions/phandle
> >      description:
> > --
> > 2.23.0
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
Sam Ravnborg Dec. 8, 2019, 9:39 a.m. UTC | #3
Hi Rob.

The panel-id can be used to help in several usecase.
With a few nits pointed out below fixed:
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

	Sam

On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> For devices that have one of several possible panels installed, the
> panel-id property gives firmware a generic way to locate and enable the
> panel node corresponding to the installed panel.  Example of how to use
> this property:
> 
>     ivo_panel {
>         compatible = "ivo,m133nwf4-r0";
>         panel-id = <0xc5>;
>         status = "disabled";
> 
>         ports {
>             port {
>                 ivo_panel_in_edp: endpoint {
>                     remote-endpoint = <&sn65dsi86_out_ivo>;
>                 };
>             };
>         };
>     };
> 
>     boe_panel {
>         compatible = "boe,nv133fhm-n61";
>         panel-id = <0xc4>;
>         status = "disabled";
> 
>         ports {
>             port {
>                 boe_panel_in_edp: endpoint {
>                     remote-endpoint = <&sn65dsi86_out_boe>;
>                 };
>             };
>         };
>     };
> 
>     sn65dsi86: bridge@2c {
>         compatible = "ti,sn65dsi86";
> 
>         ports {
>             #address-cells = <1>;
>             #size-cells = <0>;
> 
>             port@0 {
>                 reg = <0>;
>                 sn65dsi86_in_a: endpoint {
>                     remote-endpoint = <&dsi0_out>;
>                 };
>             };
> 
>             port@1 {
>                 reg = <1>;
> 
>                 sn65dsi86_out_boe: endpoint@c4 {
>                     remote-endpoint = <&boe_panel_in_edp>;
>                 };
> 
>                 sn65dsi86_out_ivo: endpoint@c5 {
>                     remote-endpoint = <&ivo_panel_in_edp>;
>                 };
>             };
>         };
>     };
> 
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> index ef8d8cdfcede..6113319b91dd 100644
> --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> @@ -75,6 +75,32 @@ properties:
>        in the device graph bindings defined in
>        Documentation/devicetree/bindings/graph.txt.
>  
> +  panel-id:
> +    description:
> +      To support the case where one of several different panels can be installed
> +      on a device, the panel-id property can be used by the firmware to identify
> +      which panel should have it's status changed to "ok".  This property is not
Use "okay" as this is waht is specified in the CT files.

> +      used by the HLOS itself.
Spell out HLOS - it is not obvious for all what it is.

> +
> +      For a device with multiple potential panels, a node for each potential
> +      should be defined with status = "disabled", and an appropriate panel-id
"potential panel should"

> +      property.  The video data producer should be setup with endpoints going to
> +      each possible panel.  The firmware will find the dt node with a panel-id
> +      matching the actual panel installed, and change it's status to "ok".
> +
> +      The exact method the firmware uses to determine the panel-id of the installed
> +      panel is outside the scope of this binding, but a few examples are
> +
> +      1) u-boot module reading a value from a u-boot env var
> +      2) EFI driver module reading a value from an EFI variable
> +      3) device specific firmware reading some device specific GPIOs or
> +         e-fuse
> +
> +      The panel-id values are an opaque integer.  They can be sparse.  The only
> +      important thing is that each possible panel in the system has a unique
> +      panel-id, and that the values configured in the device's DTB match the
> +      values that the firmware is looking for.
> +
>    ddc-i2c-bus:
>      $ref: /schemas/types.yaml#/definitions/phandle
>      description:
> -- 
> 2.23.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
Laurent Pinchart Dec. 8, 2019, 2:45 p.m. UTC | #4
Hi Rob,

Thank you for the patch.

On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> For devices that have one of several possible panels installed, the
> panel-id property gives firmware a generic way to locate and enable the
> panel node corresponding to the installed panel.  Example of how to use
> this property:
> 
>     ivo_panel {
>         compatible = "ivo,m133nwf4-r0";
>         panel-id = <0xc5>;
>         status = "disabled";
> 
>         ports {
>             port {
>                 ivo_panel_in_edp: endpoint {
>                     remote-endpoint = <&sn65dsi86_out_ivo>;
>                 };
>             };
>         };
>     };
> 
>     boe_panel {
>         compatible = "boe,nv133fhm-n61";
>         panel-id = <0xc4>;
>         status = "disabled";
> 
>         ports {
>             port {
>                 boe_panel_in_edp: endpoint {
>                     remote-endpoint = <&sn65dsi86_out_boe>;
>                 };
>             };
>         };
>     };
> 
>     sn65dsi86: bridge@2c {
>         compatible = "ti,sn65dsi86";
> 
>         ports {
>             #address-cells = <1>;
>             #size-cells = <0>;
> 
>             port@0 {
>                 reg = <0>;
>                 sn65dsi86_in_a: endpoint {
>                     remote-endpoint = <&dsi0_out>;
>                 };
>             };
> 
>             port@1 {
>                 reg = <1>;
> 
>                 sn65dsi86_out_boe: endpoint@c4 {
>                     remote-endpoint = <&boe_panel_in_edp>;
>                 };
> 
>                 sn65dsi86_out_ivo: endpoint@c5 {
>                     remote-endpoint = <&ivo_panel_in_edp>;
>                 };
>             };
>         };
>     };
> 
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> index ef8d8cdfcede..6113319b91dd 100644
> --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> @@ -75,6 +75,32 @@ properties:
>        in the device graph bindings defined in
>        Documentation/devicetree/bindings/graph.txt.
>  
> +  panel-id:
> +    description:
> +      To support the case where one of several different panels can be installed
> +      on a device, the panel-id property can be used by the firmware to identify
> +      which panel should have it's status changed to "ok".  This property is not
> +      used by the HLOS itself.

If your firmware can modify the status property of a panel, it can also
add DT nodes. As discussed before, I don't think this belongs to DT.
Even if panel-id isn't used by the operating system, you have Linux
kernel patches in this series that show that this isn't transparent.

This needs to be handled in the firmware (or, if not possible, in a
kernel board driver). The above DT fragment, visible to the kernel,
doesn't describe the actual hardware. Furthermore, you would require all
bridge drivers to be patched to support this method, which shows again
that the issue isn't handled in the right place.

Finally, unless I'm mistaken, this series is meant to support display
for an ACPI-based ARM machine. Using DT as a stop-gap measure because
ACPI support isn't there yet is fine out-of-tree, and fine by me in-tree
provided that the DT bindings are clean, but not when DT is abused like
this.

I'm sorry, but this is a NACK from me. Please handle this transparently
in the firmware if you want DT-based boot, or with ACPI.

> +
> +      For a device with multiple potential panels, a node for each potential
> +      should be defined with status = "disabled", and an appropriate panel-id
> +      property.  The video data producer should be setup with endpoints going to
> +      each possible panel.  The firmware will find the dt node with a panel-id
> +      matching the actual panel installed, and change it's status to "ok".
> +
> +      The exact method the firmware uses to determine the panel-id of the installed
> +      panel is outside the scope of this binding, but a few examples are
> +
> +      1) u-boot module reading a value from a u-boot env var
> +      2) EFI driver module reading a value from an EFI variable
> +      3) device specific firmware reading some device specific GPIOs or
> +         e-fuse
> +
> +      The panel-id values are an opaque integer.  They can be sparse.  The only
> +      important thing is that each possible panel in the system has a unique
> +      panel-id, and that the values configured in the device's DTB match the
> +      values that the firmware is looking for.
> +
>    ddc-i2c-bus:
>      $ref: /schemas/types.yaml#/definitions/phandle
>      description:
Rob Clark Dec. 8, 2019, 4:50 p.m. UTC | #5
On Sun, Dec 8, 2019 at 6:45 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Rob,
>
> Thank you for the patch.
>
> On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> > From: Rob Clark <robdclark@chromium.org>
> >
> > For devices that have one of several possible panels installed, the
> > panel-id property gives firmware a generic way to locate and enable the
> > panel node corresponding to the installed panel.  Example of how to use
> > this property:
> >
> >     ivo_panel {
> >         compatible = "ivo,m133nwf4-r0";
> >         panel-id = <0xc5>;
> >         status = "disabled";
> >
> >         ports {
> >             port {
> >                 ivo_panel_in_edp: endpoint {
> >                     remote-endpoint = <&sn65dsi86_out_ivo>;
> >                 };
> >             };
> >         };
> >     };
> >
> >     boe_panel {
> >         compatible = "boe,nv133fhm-n61";
> >         panel-id = <0xc4>;
> >         status = "disabled";
> >
> >         ports {
> >             port {
> >                 boe_panel_in_edp: endpoint {
> >                     remote-endpoint = <&sn65dsi86_out_boe>;
> >                 };
> >             };
> >         };
> >     };
> >
> >     sn65dsi86: bridge@2c {
> >         compatible = "ti,sn65dsi86";
> >
> >         ports {
> >             #address-cells = <1>;
> >             #size-cells = <0>;
> >
> >             port@0 {
> >                 reg = <0>;
> >                 sn65dsi86_in_a: endpoint {
> >                     remote-endpoint = <&dsi0_out>;
> >                 };
> >             };
> >
> >             port@1 {
> >                 reg = <1>;
> >
> >                 sn65dsi86_out_boe: endpoint@c4 {
> >                     remote-endpoint = <&boe_panel_in_edp>;
> >                 };
> >
> >                 sn65dsi86_out_ivo: endpoint@c5 {
> >                     remote-endpoint = <&ivo_panel_in_edp>;
> >                 };
> >             };
> >         };
> >     };
> >
> > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > ---
> >  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > index ef8d8cdfcede..6113319b91dd 100644
> > --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > @@ -75,6 +75,32 @@ properties:
> >        in the device graph bindings defined in
> >        Documentation/devicetree/bindings/graph.txt.
> >
> > +  panel-id:
> > +    description:
> > +      To support the case where one of several different panels can be installed
> > +      on a device, the panel-id property can be used by the firmware to identify
> > +      which panel should have it's status changed to "ok".  This property is not
> > +      used by the HLOS itself.
>
> If your firmware can modify the status property of a panel, it can also
> add DT nodes. As discussed before, I don't think this belongs to DT.
> Even if panel-id isn't used by the operating system, you have Linux
> kernel patches in this series that show that this isn't transparent.

I've already explained several times why this is not feasible.  It
would require DtbLoader to be familiar with each individual device,
and be rev'd every time a new device appears.  That is not practical
at all.

(And fwiw, the ACPI tables describe each panel.. with an ACPI method
that is passed the the panel-id and returns the appropriate table..
since DT doesn't have methods, this is the solution.)

I stand by this patch, we can't keep running away from this problem
and wave the magic firmware wand.

BR,
-R


> This needs to be handled in the firmware (or, if not possible, in a
> kernel board driver). The above DT fragment, visible to the kernel,
> doesn't describe the actual hardware. Furthermore, you would require all
> bridge drivers to be patched to support this method, which shows again
> that the issue isn't handled in the right place.
>
> Finally, unless I'm mistaken, this series is meant to support display
> for an ACPI-based ARM machine. Using DT as a stop-gap measure because
> ACPI support isn't there yet is fine out-of-tree, and fine by me in-tree
> provided that the DT bindings are clean, but not when DT is abused like
> this.
>
> I'm sorry, but this is a NACK from me. Please handle this transparently
> in the firmware if you want DT-based boot, or with ACPI.
>
> > +
> > +      For a device with multiple potential panels, a node for each potential
> > +      should be defined with status = "disabled", and an appropriate panel-id
> > +      property.  The video data producer should be setup with endpoints going to
> > +      each possible panel.  The firmware will find the dt node with a panel-id
> > +      matching the actual panel installed, and change it's status to "ok".
> > +
> > +      The exact method the firmware uses to determine the panel-id of the installed
> > +      panel is outside the scope of this binding, but a few examples are
> > +
> > +      1) u-boot module reading a value from a u-boot env var
> > +      2) EFI driver module reading a value from an EFI variable
> > +      3) device specific firmware reading some device specific GPIOs or
> > +         e-fuse
> > +
> > +      The panel-id values are an opaque integer.  They can be sparse.  The only
> > +      important thing is that each possible panel in the system has a unique
> > +      panel-id, and that the values configured in the device's DTB match the
> > +      values that the firmware is looking for.
> > +
> >    ddc-i2c-bus:
> >      $ref: /schemas/types.yaml#/definitions/phandle
> >      description:
>
> --
> Regards,
>
> Laurent Pinchart
Laurent Pinchart Dec. 8, 2019, 6:27 p.m. UTC | #6
Hi Rob,

On Sun, Dec 08, 2019 at 08:50:32AM -0800, Rob Clark wrote:
> On Sun, Dec 8, 2019 at 6:45 AM Laurent Pinchart wrote:
> > On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> > > From: Rob Clark <robdclark@chromium.org>
> > >
> > > For devices that have one of several possible panels installed, the
> > > panel-id property gives firmware a generic way to locate and enable the
> > > panel node corresponding to the installed panel.  Example of how to use
> > > this property:
> > >
> > >     ivo_panel {
> > >         compatible = "ivo,m133nwf4-r0";
> > >         panel-id = <0xc5>;
> > >         status = "disabled";
> > >
> > >         ports {
> > >             port {
> > >                 ivo_panel_in_edp: endpoint {
> > >                     remote-endpoint = <&sn65dsi86_out_ivo>;
> > >                 };
> > >             };
> > >         };
> > >     };
> > >
> > >     boe_panel {
> > >         compatible = "boe,nv133fhm-n61";
> > >         panel-id = <0xc4>;
> > >         status = "disabled";
> > >
> > >         ports {
> > >             port {
> > >                 boe_panel_in_edp: endpoint {
> > >                     remote-endpoint = <&sn65dsi86_out_boe>;
> > >                 };
> > >             };
> > >         };
> > >     };
> > >
> > >     sn65dsi86: bridge@2c {
> > >         compatible = "ti,sn65dsi86";
> > >
> > >         ports {
> > >             #address-cells = <1>;
> > >             #size-cells = <0>;
> > >
> > >             port@0 {
> > >                 reg = <0>;
> > >                 sn65dsi86_in_a: endpoint {
> > >                     remote-endpoint = <&dsi0_out>;
> > >                 };
> > >             };
> > >
> > >             port@1 {
> > >                 reg = <1>;
> > >
> > >                 sn65dsi86_out_boe: endpoint@c4 {
> > >                     remote-endpoint = <&boe_panel_in_edp>;
> > >                 };
> > >
> > >                 sn65dsi86_out_ivo: endpoint@c5 {
> > >                     remote-endpoint = <&ivo_panel_in_edp>;
> > >                 };
> > >             };
> > >         };
> > >     };
> > >
> > > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > > ---
> > >  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
> > >  1 file changed, 26 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > index ef8d8cdfcede..6113319b91dd 100644
> > > --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > @@ -75,6 +75,32 @@ properties:
> > >        in the device graph bindings defined in
> > >        Documentation/devicetree/bindings/graph.txt.
> > >
> > > +  panel-id:
> > > +    description:
> > > +      To support the case where one of several different panels can be installed
> > > +      on a device, the panel-id property can be used by the firmware to identify
> > > +      which panel should have it's status changed to "ok".  This property is not
> > > +      used by the HLOS itself.
> >
> > If your firmware can modify the status property of a panel, it can also
> > add DT nodes. As discussed before, I don't think this belongs to DT.
> > Even if panel-id isn't used by the operating system, you have Linux
> > kernel patches in this series that show that this isn't transparent.
> 
> I've already explained several times why this is not feasible.  It
> would require DtbLoader to be familiar with each individual device,
> and be rev'd every time a new device appears.  That is not practical
> at all.
> 
> (And fwiw, the ACPI tables describe each panel.. with an ACPI method
> that is passed the the panel-id and returns the appropriate table..
> since DT doesn't have methods, this is the solution.)
> 
> I stand by this patch, we can't keep running away from this problem
> and wave the magic firmware wand.

I believe in firmware solutions more than firmware magic wands :-)

While device-specific knowledge in DtbLoader is indeed not practical,
you still need device-specific knowledge at the firmware level in the
sense that you pass a device-specific DT binary to DtbLoader to be
patched based on the panel ID. The device-specific information required
at the firmware level can thus be expressed as data instead of code.

I understand it wouldn't be practical for DtbLoader to receive two
independent pieces of device-specific data (the DT binary and another
custom data blob). Why couldn't however DtbLoader get a DT binary as
described in the commit message of this patch, and strip off all the
panel nodes that are not applicable to the platform, as well as the
panel-id property ? This would be completely transparent on the OS side,
and would not require patching DtbLoader for every device, as all the
information required would be present in a single DT binary, encoded
using DT syntax.

Ths would create a dichotomy in the DT bindings, in the sense that we
would have bindings applicable to the boot loader only, and bindings for
the OS, but this is already the case in what you're proposing here as
the panel-id property is documented as not used by the OS itself.

> > This needs to be handled in the firmware (or, if not possible, in a
> > kernel board driver). The above DT fragment, visible to the kernel,
> > doesn't describe the actual hardware. Furthermore, you would require all
> > bridge drivers to be patched to support this method, which shows again
> > that the issue isn't handled in the right place.
> >
> > Finally, unless I'm mistaken, this series is meant to support display
> > for an ACPI-based ARM machine. Using DT as a stop-gap measure because
> > ACPI support isn't there yet is fine out-of-tree, and fine by me in-tree
> > provided that the DT bindings are clean, but not when DT is abused like
> > this.
> >
> > I'm sorry, but this is a NACK from me. Please handle this transparently
> > in the firmware if you want DT-based boot, or with ACPI.
> >
> > > +
> > > +      For a device with multiple potential panels, a node for each potential
> > > +      should be defined with status = "disabled", and an appropriate panel-id
> > > +      property.  The video data producer should be setup with endpoints going to
> > > +      each possible panel.  The firmware will find the dt node with a panel-id
> > > +      matching the actual panel installed, and change it's status to "ok".
> > > +
> > > +      The exact method the firmware uses to determine the panel-id of the installed
> > > +      panel is outside the scope of this binding, but a few examples are
> > > +
> > > +      1) u-boot module reading a value from a u-boot env var
> > > +      2) EFI driver module reading a value from an EFI variable
> > > +      3) device specific firmware reading some device specific GPIOs or
> > > +         e-fuse
> > > +
> > > +      The panel-id values are an opaque integer.  They can be sparse.  The only
> > > +      important thing is that each possible panel in the system has a unique
> > > +      panel-id, and that the values configured in the device's DTB match the
> > > +      values that the firmware is looking for.
> > > +
> > >    ddc-i2c-bus:
> > >      $ref: /schemas/types.yaml#/definitions/phandle
> > >      description:
Rob Clark Dec. 8, 2019, 9:23 p.m. UTC | #7
On Sun, Dec 8, 2019 at 10:28 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Rob,
>
> On Sun, Dec 08, 2019 at 08:50:32AM -0800, Rob Clark wrote:
> > On Sun, Dec 8, 2019 at 6:45 AM Laurent Pinchart wrote:
> > > On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> > > > From: Rob Clark <robdclark@chromium.org>
> > > >
> > > > For devices that have one of several possible panels installed, the
> > > > panel-id property gives firmware a generic way to locate and enable the
> > > > panel node corresponding to the installed panel.  Example of how to use
> > > > this property:
> > > >
> > > >     ivo_panel {
> > > >         compatible = "ivo,m133nwf4-r0";
> > > >         panel-id = <0xc5>;
> > > >         status = "disabled";
> > > >
> > > >         ports {
> > > >             port {
> > > >                 ivo_panel_in_edp: endpoint {
> > > >                     remote-endpoint = <&sn65dsi86_out_ivo>;
> > > >                 };
> > > >             };
> > > >         };
> > > >     };
> > > >
> > > >     boe_panel {
> > > >         compatible = "boe,nv133fhm-n61";
> > > >         panel-id = <0xc4>;
> > > >         status = "disabled";
> > > >
> > > >         ports {
> > > >             port {
> > > >                 boe_panel_in_edp: endpoint {
> > > >                     remote-endpoint = <&sn65dsi86_out_boe>;
> > > >                 };
> > > >             };
> > > >         };
> > > >     };
> > > >
> > > >     sn65dsi86: bridge@2c {
> > > >         compatible = "ti,sn65dsi86";
> > > >
> > > >         ports {
> > > >             #address-cells = <1>;
> > > >             #size-cells = <0>;
> > > >
> > > >             port@0 {
> > > >                 reg = <0>;
> > > >                 sn65dsi86_in_a: endpoint {
> > > >                     remote-endpoint = <&dsi0_out>;
> > > >                 };
> > > >             };
> > > >
> > > >             port@1 {
> > > >                 reg = <1>;
> > > >
> > > >                 sn65dsi86_out_boe: endpoint@c4 {
> > > >                     remote-endpoint = <&boe_panel_in_edp>;
> > > >                 };
> > > >
> > > >                 sn65dsi86_out_ivo: endpoint@c5 {
> > > >                     remote-endpoint = <&ivo_panel_in_edp>;
> > > >                 };
> > > >             };
> > > >         };
> > > >     };
> > > >
> > > > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > > > ---
> > > >  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
> > > >  1 file changed, 26 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > index ef8d8cdfcede..6113319b91dd 100644
> > > > --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > @@ -75,6 +75,32 @@ properties:
> > > >        in the device graph bindings defined in
> > > >        Documentation/devicetree/bindings/graph.txt.
> > > >
> > > > +  panel-id:
> > > > +    description:
> > > > +      To support the case where one of several different panels can be installed
> > > > +      on a device, the panel-id property can be used by the firmware to identify
> > > > +      which panel should have it's status changed to "ok".  This property is not
> > > > +      used by the HLOS itself.
> > >
> > > If your firmware can modify the status property of a panel, it can also
> > > add DT nodes. As discussed before, I don't think this belongs to DT.
> > > Even if panel-id isn't used by the operating system, you have Linux
> > > kernel patches in this series that show that this isn't transparent.
> >
> > I've already explained several times why this is not feasible.  It
> > would require DtbLoader to be familiar with each individual device,
> > and be rev'd every time a new device appears.  That is not practical
> > at all.
> >
> > (And fwiw, the ACPI tables describe each panel.. with an ACPI method
> > that is passed the the panel-id and returns the appropriate table..
> > since DT doesn't have methods, this is the solution.)
> >
> > I stand by this patch, we can't keep running away from this problem
> > and wave the magic firmware wand.
>
> I believe in firmware solutions more than firmware magic wands :-)
>

and with that in mind, I think I've come up with a firmware solution,
in the form of dtb overlays :-)

I've managed to get DtbLoader to find and load a panel overlay based
on the panel-id it reads, which drops all patches in the patchset
except the last one, which now has this delta:

---------
diff --git a/arch/arm64/boot/dts/qcom/Makefile
b/arch/arm64/boot/dts/qcom/Makefile
index 6498a1ec893f..1a61e8da2521 100644
--- a/arch/arm64/boot/dts/qcom/Makefile
+++ b/arch/arm64/boot/dts/qcom/Makefile
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
+subdir-y += panels
 dtb-$(CONFIG_ARCH_QCOM)    += apq8016-sbc.dtb
 dtb-$(CONFIG_ARCH_QCOM)    += apq8096-db820c.dtb
 dtb-$(CONFIG_ARCH_QCOM)    += ipq8074-hk01.dtb
diff --git a/arch/arm64/boot/dts/qcom/panels/Makefile
b/arch/arm64/boot/dts/qcom/panels/Makefile
new file mode 100644
index 000000000000..dbf55f423555
--- /dev/null
+++ b/arch/arm64/boot/dts/qcom/panels/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+dtb-$(CONFIG_ARCH_QCOM) += panel-c4.dtb
+dtb-$(CONFIG_ARCH_QCOM) += panel-c5.dtb
diff --git a/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
b/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
new file mode 100644
index 000000000000..ebcf65419dad
--- /dev/null
+++ b/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Panel overlay for panel-id 0xc4
+ *
+ * Copyright (c) 2019, Linaro Ltd.
+ */
+
+/dts-v1/;
+/plugin/;
+/ {
+    fragment@0 {
+        target-path = "/panel";
+        __overlay__ {
+            compatible = "boe,nv133fhm-n61";
+        };
+    };
+};
diff --git a/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
b/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
new file mode 100644
index 000000000000..0ad5bb6003e3
--- /dev/null
+++ b/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Panel overlay for panel-id 0xc5
+ *
+ * Copyright (c) 2019, Linaro Ltd.
+ */
+
+/dts-v1/;
+/plugin/;
+/ {
+    fragment@0 {
+        target-path = "/panel";
+        __overlay__ {
+            compatible = "ivo,m133nwf4-r0";
+        };
+    };
+};
diff --git a/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
b/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
index c35d8099d8eb..92c76afb721c 100644
--- a/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
+++ b/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
@@ -22,11 +22,13 @@
         hsuart0 = &uart6;
     };

+    /*
+     * stub node which defines how panel is connected to bridge, which
+     * will be updated by panel specific overlay
+     */
     panel {
-        compatible = "ivo,m133nwf4-r0";
         power-supply = <&vlcm_3v3>;
         no-hpd;
-
         ports {
             port {
                 panel_in_edp: endpoint {
---------

Side note, try as I might, I couldn't get the 'target = <&phandle>'
approach to work in the overlays, so I ended up going with target-path
instead.  From digging thru the fdt_overlay code, I *think* it is
because I end up w/ an overlay dtb without symbols.  In the end, I
guess target-path works just as well.


BR,
-R
Laurent Pinchart Dec. 9, 2019, 11:05 a.m. UTC | #8
Hi Rob,

On Sun, Dec 08, 2019 at 01:23:59PM -0800, Rob Clark wrote:
> On Sun, Dec 8, 2019 at 10:28 AM Laurent Pinchart wrote:
> > On Sun, Dec 08, 2019 at 08:50:32AM -0800, Rob Clark wrote:
> > > On Sun, Dec 8, 2019 at 6:45 AM Laurent Pinchart wrote:
> > > > On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> > > > > From: Rob Clark <robdclark@chromium.org>
> > > > >
> > > > > For devices that have one of several possible panels installed, the
> > > > > panel-id property gives firmware a generic way to locate and enable the
> > > > > panel node corresponding to the installed panel.  Example of how to use
> > > > > this property:
> > > > >
> > > > >     ivo_panel {
> > > > >         compatible = "ivo,m133nwf4-r0";
> > > > >         panel-id = <0xc5>;
> > > > >         status = "disabled";
> > > > >
> > > > >         ports {
> > > > >             port {
> > > > >                 ivo_panel_in_edp: endpoint {
> > > > >                     remote-endpoint = <&sn65dsi86_out_ivo>;
> > > > >                 };
> > > > >             };
> > > > >         };
> > > > >     };
> > > > >
> > > > >     boe_panel {
> > > > >         compatible = "boe,nv133fhm-n61";
> > > > >         panel-id = <0xc4>;
> > > > >         status = "disabled";
> > > > >
> > > > >         ports {
> > > > >             port {
> > > > >                 boe_panel_in_edp: endpoint {
> > > > >                     remote-endpoint = <&sn65dsi86_out_boe>;
> > > > >                 };
> > > > >             };
> > > > >         };
> > > > >     };
> > > > >
> > > > >     sn65dsi86: bridge@2c {
> > > > >         compatible = "ti,sn65dsi86";
> > > > >
> > > > >         ports {
> > > > >             #address-cells = <1>;
> > > > >             #size-cells = <0>;
> > > > >
> > > > >             port@0 {
> > > > >                 reg = <0>;
> > > > >                 sn65dsi86_in_a: endpoint {
> > > > >                     remote-endpoint = <&dsi0_out>;
> > > > >                 };
> > > > >             };
> > > > >
> > > > >             port@1 {
> > > > >                 reg = <1>;
> > > > >
> > > > >                 sn65dsi86_out_boe: endpoint@c4 {
> > > > >                     remote-endpoint = <&boe_panel_in_edp>;
> > > > >                 };
> > > > >
> > > > >                 sn65dsi86_out_ivo: endpoint@c5 {
> > > > >                     remote-endpoint = <&ivo_panel_in_edp>;
> > > > >                 };
> > > > >             };
> > > > >         };
> > > > >     };
> > > > >
> > > > > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > > > > ---
> > > > >  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
> > > > >  1 file changed, 26 insertions(+)
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > index ef8d8cdfcede..6113319b91dd 100644
> > > > > --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > @@ -75,6 +75,32 @@ properties:
> > > > >        in the device graph bindings defined in
> > > > >        Documentation/devicetree/bindings/graph.txt.
> > > > >
> > > > > +  panel-id:
> > > > > +    description:
> > > > > +      To support the case where one of several different panels can be installed
> > > > > +      on a device, the panel-id property can be used by the firmware to identify
> > > > > +      which panel should have it's status changed to "ok".  This property is not
> > > > > +      used by the HLOS itself.
> > > >
> > > > If your firmware can modify the status property of a panel, it can also
> > > > add DT nodes. As discussed before, I don't think this belongs to DT.
> > > > Even if panel-id isn't used by the operating system, you have Linux
> > > > kernel patches in this series that show that this isn't transparent.
> > >
> > > I've already explained several times why this is not feasible.  It
> > > would require DtbLoader to be familiar with each individual device,
> > > and be rev'd every time a new device appears.  That is not practical
> > > at all.
> > >
> > > (And fwiw, the ACPI tables describe each panel.. with an ACPI method
> > > that is passed the the panel-id and returns the appropriate table..
> > > since DT doesn't have methods, this is the solution.)
> > >
> > > I stand by this patch, we can't keep running away from this problem
> > > and wave the magic firmware wand.
> >
> > I believe in firmware solutions more than firmware magic wands :-)
> 
> and with that in mind, I think I've come up with a firmware solution,
> in the form of dtb overlays :-)
> 
> I've managed to get DtbLoader to find and load a panel overlay based
> on the panel-id it reads, which drops all patches in the patchset
> except the last one, which now has this delta:

Thank you for looking into this, I really like the outcome :-)

> ---------
> diff --git a/arch/arm64/boot/dts/qcom/Makefile
> b/arch/arm64/boot/dts/qcom/Makefile
> index 6498a1ec893f..1a61e8da2521 100644
> --- a/arch/arm64/boot/dts/qcom/Makefile
> +++ b/arch/arm64/boot/dts/qcom/Makefile
> @@ -1,4 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0
> +subdir-y += panels
>  dtb-$(CONFIG_ARCH_QCOM)    += apq8016-sbc.dtb
>  dtb-$(CONFIG_ARCH_QCOM)    += apq8096-db820c.dtb
>  dtb-$(CONFIG_ARCH_QCOM)    += ipq8074-hk01.dtb
> diff --git a/arch/arm64/boot/dts/qcom/panels/Makefile
> b/arch/arm64/boot/dts/qcom/panels/Makefile
> new file mode 100644
> index 000000000000..dbf55f423555
> --- /dev/null
> +++ b/arch/arm64/boot/dts/qcom/panels/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +dtb-$(CONFIG_ARCH_QCOM) += panel-c4.dtb
> +dtb-$(CONFIG_ARCH_QCOM) += panel-c5.dtb
> diff --git a/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> b/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> new file mode 100644
> index 000000000000..ebcf65419dad
> --- /dev/null
> +++ b/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> @@ -0,0 +1,17 @@
> +// SPDX-License-Identifier: BSD-3-Clause
> +/*
> + * Panel overlay for panel-id 0xc4
> + *
> + * Copyright (c) 2019, Linaro Ltd.
> + */
> +
> +/dts-v1/;
> +/plugin/;
> +/ {
> +    fragment@0 {
> +        target-path = "/panel";
> +        __overlay__ {
> +            compatible = "boe,nv133fhm-n61";
> +        };
> +    };
> +};
> diff --git a/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> b/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> new file mode 100644
> index 000000000000..0ad5bb6003e3
> --- /dev/null
> +++ b/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> @@ -0,0 +1,17 @@
> +// SPDX-License-Identifier: BSD-3-Clause
> +/*
> + * Panel overlay for panel-id 0xc5
> + *
> + * Copyright (c) 2019, Linaro Ltd.
> + */
> +
> +/dts-v1/;
> +/plugin/;
> +/ {
> +    fragment@0 {
> +        target-path = "/panel";
> +        __overlay__ {
> +            compatible = "ivo,m133nwf4-r0";
> +        };
> +    };
> +};
> diff --git a/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> b/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> index c35d8099d8eb..92c76afb721c 100644
> --- a/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> +++ b/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> @@ -22,11 +22,13 @@
>          hsuart0 = &uart6;
>      };
> 
> +    /*
> +     * stub node which defines how panel is connected to bridge, which
> +     * will be updated by panel specific overlay
> +     */
>      panel {
> -        compatible = "ivo,m133nwf4-r0";
>          power-supply = <&vlcm_3v3>;
>          no-hpd;
> -
>          ports {
>              port {
>                  panel_in_edp: endpoint {
> ---------
> 
> Side note, try as I might, I couldn't get the 'target = <&phandle>'
> approach to work in the overlays, so I ended up going with target-path
> instead.  From digging thru the fdt_overlay code, I *think* it is
> because I end up w/ an overlay dtb without symbols.  In the end, I
> guess target-path works just as well.
Rob Herring Dec. 9, 2019, 3:31 p.m. UTC | #9
On Sun, Dec 8, 2019 at 3:24 PM Rob Clark <robdclark@gmail.com> wrote:
>
> On Sun, Dec 8, 2019 at 10:28 AM Laurent Pinchart
> <laurent.pinchart@ideasonboard.com> wrote:
> >
> > Hi Rob,
> >
> > On Sun, Dec 08, 2019 at 08:50:32AM -0800, Rob Clark wrote:
> > > On Sun, Dec 8, 2019 at 6:45 AM Laurent Pinchart wrote:
> > > > On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> > > > > From: Rob Clark <robdclark@chromium.org>
> > > > >
> > > > > For devices that have one of several possible panels installed, the
> > > > > panel-id property gives firmware a generic way to locate and enable the
> > > > > panel node corresponding to the installed panel.  Example of how to use
> > > > > this property:
> > > > >
> > > > >     ivo_panel {
> > > > >         compatible = "ivo,m133nwf4-r0";
> > > > >         panel-id = <0xc5>;
> > > > >         status = "disabled";
> > > > >
> > > > >         ports {
> > > > >             port {
> > > > >                 ivo_panel_in_edp: endpoint {
> > > > >                     remote-endpoint = <&sn65dsi86_out_ivo>;
> > > > >                 };
> > > > >             };
> > > > >         };
> > > > >     };
> > > > >
> > > > >     boe_panel {
> > > > >         compatible = "boe,nv133fhm-n61";
> > > > >         panel-id = <0xc4>;
> > > > >         status = "disabled";
> > > > >
> > > > >         ports {
> > > > >             port {
> > > > >                 boe_panel_in_edp: endpoint {
> > > > >                     remote-endpoint = <&sn65dsi86_out_boe>;
> > > > >                 };
> > > > >             };
> > > > >         };
> > > > >     };
> > > > >
> > > > >     sn65dsi86: bridge@2c {
> > > > >         compatible = "ti,sn65dsi86";
> > > > >
> > > > >         ports {
> > > > >             #address-cells = <1>;
> > > > >             #size-cells = <0>;
> > > > >
> > > > >             port@0 {
> > > > >                 reg = <0>;
> > > > >                 sn65dsi86_in_a: endpoint {
> > > > >                     remote-endpoint = <&dsi0_out>;
> > > > >                 };
> > > > >             };
> > > > >
> > > > >             port@1 {
> > > > >                 reg = <1>;
> > > > >
> > > > >                 sn65dsi86_out_boe: endpoint@c4 {
> > > > >                     remote-endpoint = <&boe_panel_in_edp>;
> > > > >                 };
> > > > >
> > > > >                 sn65dsi86_out_ivo: endpoint@c5 {
> > > > >                     remote-endpoint = <&ivo_panel_in_edp>;
> > > > >                 };
> > > > >             };
> > > > >         };
> > > > >     };
> > > > >
> > > > > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > > > > ---
> > > > >  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
> > > > >  1 file changed, 26 insertions(+)
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > index ef8d8cdfcede..6113319b91dd 100644
> > > > > --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > @@ -75,6 +75,32 @@ properties:
> > > > >        in the device graph bindings defined in
> > > > >        Documentation/devicetree/bindings/graph.txt.
> > > > >
> > > > > +  panel-id:
> > > > > +    description:
> > > > > +      To support the case where one of several different panels can be installed
> > > > > +      on a device, the panel-id property can be used by the firmware to identify
> > > > > +      which panel should have it's status changed to "ok".  This property is not
> > > > > +      used by the HLOS itself.
> > > >
> > > > If your firmware can modify the status property of a panel, it can also
> > > > add DT nodes. As discussed before, I don't think this belongs to DT.
> > > > Even if panel-id isn't used by the operating system, you have Linux
> > > > kernel patches in this series that show that this isn't transparent.
> > >
> > > I've already explained several times why this is not feasible.  It
> > > would require DtbLoader to be familiar with each individual device,
> > > and be rev'd every time a new device appears.  That is not practical
> > > at all.
> > >
> > > (And fwiw, the ACPI tables describe each panel.. with an ACPI method
> > > that is passed the the panel-id and returns the appropriate table..
> > > since DT doesn't have methods, this is the solution.)
> > >
> > > I stand by this patch, we can't keep running away from this problem
> > > and wave the magic firmware wand.
> >
> > I believe in firmware solutions more than firmware magic wands :-)
> >
>
> and with that in mind, I think I've come up with a firmware solution,
> in the form of dtb overlays :-)
>
> I've managed to get DtbLoader to find and load a panel overlay based
> on the panel-id it reads, which drops all patches in the patchset
> except the last one, which now has this delta:

This looks good to me. The only slight concern I have with it is
making the overlay filename an ABI. I don't have a better suggestion
though. How would this work for other vendors or the same panel ID
(for different panels) used on different platforms? For different
vendors at least, I guess dtbloader gets the base dtb path somehow and
the overlay's are relative to that?

> ---------
> diff --git a/arch/arm64/boot/dts/qcom/Makefile
> b/arch/arm64/boot/dts/qcom/Makefile
> index 6498a1ec893f..1a61e8da2521 100644
> --- a/arch/arm64/boot/dts/qcom/Makefile
> +++ b/arch/arm64/boot/dts/qcom/Makefile
> @@ -1,4 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0
> +subdir-y += panels
>  dtb-$(CONFIG_ARCH_QCOM)    += apq8016-sbc.dtb
>  dtb-$(CONFIG_ARCH_QCOM)    += apq8096-db820c.dtb
>  dtb-$(CONFIG_ARCH_QCOM)    += ipq8074-hk01.dtb
> diff --git a/arch/arm64/boot/dts/qcom/panels/Makefile
> b/arch/arm64/boot/dts/qcom/panels/Makefile
> new file mode 100644
> index 000000000000..dbf55f423555
> --- /dev/null
> +++ b/arch/arm64/boot/dts/qcom/panels/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +dtb-$(CONFIG_ARCH_QCOM) += panel-c4.dtb
> +dtb-$(CONFIG_ARCH_QCOM) += panel-c5.dtb
> diff --git a/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> b/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> new file mode 100644
> index 000000000000..ebcf65419dad
> --- /dev/null
> +++ b/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> @@ -0,0 +1,17 @@
> +// SPDX-License-Identifier: BSD-3-Clause
> +/*
> + * Panel overlay for panel-id 0xc4
> + *
> + * Copyright (c) 2019, Linaro Ltd.
> + */
> +
> +/dts-v1/;
> +/plugin/;
> +/ {
> +    fragment@0 {
> +        target-path = "/panel";
> +        __overlay__ {
> +            compatible = "boe,nv133fhm-n61";
> +        };
> +    };
> +};
> diff --git a/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> b/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> new file mode 100644
> index 000000000000..0ad5bb6003e3
> --- /dev/null
> +++ b/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> @@ -0,0 +1,17 @@
> +// SPDX-License-Identifier: BSD-3-Clause
> +/*
> + * Panel overlay for panel-id 0xc5
> + *
> + * Copyright (c) 2019, Linaro Ltd.
> + */
> +
> +/dts-v1/;
> +/plugin/;
> +/ {
> +    fragment@0 {
> +        target-path = "/panel";
> +        __overlay__ {
> +            compatible = "ivo,m133nwf4-r0";
> +        };
> +    };
> +};
> diff --git a/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> b/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> index c35d8099d8eb..92c76afb721c 100644
> --- a/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> +++ b/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> @@ -22,11 +22,13 @@
>          hsuart0 = &uart6;
>      };
>
> +    /*
> +     * stub node which defines how panel is connected to bridge, which
> +     * will be updated by panel specific overlay
> +     */
>      panel {
> -        compatible = "ivo,m133nwf4-r0";
>          power-supply = <&vlcm_3v3>;
>          no-hpd;
> -
>          ports {
>              port {
>                  panel_in_edp: endpoint {
> ---------
>
> Side note, try as I might, I couldn't get the 'target = <&phandle>'
> approach to work in the overlays, so I ended up going with target-path
> instead.  From digging thru the fdt_overlay code, I *think* it is
> because I end up w/ an overlay dtb without symbols.  In the end, I
> guess target-path works just as well.

It's the base dtb that needs the symbols I think.

BTW, to answer the question on #dri-devel, if you wanted to put the
full panel into an overlay, the way to solve the problem of having
bridge specific knowledge is defining a connector node. That should
provide enough abstraction. Presumably the connector is actually the
same across panels in this situation, so that should match up with the
actual h/w. It could be possible to have a different physical
connector populated for each possible panel, but hopefully that's not
the common case.

Rob
Rob Clark Dec. 9, 2019, 3:57 p.m. UTC | #10
On Mon, Dec 9, 2019 at 7:31 AM Rob Herring <robh+dt@kernel.org> wrote:
>
> On Sun, Dec 8, 2019 at 3:24 PM Rob Clark <robdclark@gmail.com> wrote:
> >
> > On Sun, Dec 8, 2019 at 10:28 AM Laurent Pinchart
> > <laurent.pinchart@ideasonboard.com> wrote:
> > >
> > > Hi Rob,
> > >
> > > On Sun, Dec 08, 2019 at 08:50:32AM -0800, Rob Clark wrote:
> > > > On Sun, Dec 8, 2019 at 6:45 AM Laurent Pinchart wrote:
> > > > > On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> > > > > > From: Rob Clark <robdclark@chromium.org>
> > > > > >
> > > > > > For devices that have one of several possible panels installed, the
> > > > > > panel-id property gives firmware a generic way to locate and enable the
> > > > > > panel node corresponding to the installed panel.  Example of how to use
> > > > > > this property:
> > > > > >
> > > > > >     ivo_panel {
> > > > > >         compatible = "ivo,m133nwf4-r0";
> > > > > >         panel-id = <0xc5>;
> > > > > >         status = "disabled";
> > > > > >
> > > > > >         ports {
> > > > > >             port {
> > > > > >                 ivo_panel_in_edp: endpoint {
> > > > > >                     remote-endpoint = <&sn65dsi86_out_ivo>;
> > > > > >                 };
> > > > > >             };
> > > > > >         };
> > > > > >     };
> > > > > >
> > > > > >     boe_panel {
> > > > > >         compatible = "boe,nv133fhm-n61";
> > > > > >         panel-id = <0xc4>;
> > > > > >         status = "disabled";
> > > > > >
> > > > > >         ports {
> > > > > >             port {
> > > > > >                 boe_panel_in_edp: endpoint {
> > > > > >                     remote-endpoint = <&sn65dsi86_out_boe>;
> > > > > >                 };
> > > > > >             };
> > > > > >         };
> > > > > >     };
> > > > > >
> > > > > >     sn65dsi86: bridge@2c {
> > > > > >         compatible = "ti,sn65dsi86";
> > > > > >
> > > > > >         ports {
> > > > > >             #address-cells = <1>;
> > > > > >             #size-cells = <0>;
> > > > > >
> > > > > >             port@0 {
> > > > > >                 reg = <0>;
> > > > > >                 sn65dsi86_in_a: endpoint {
> > > > > >                     remote-endpoint = <&dsi0_out>;
> > > > > >                 };
> > > > > >             };
> > > > > >
> > > > > >             port@1 {
> > > > > >                 reg = <1>;
> > > > > >
> > > > > >                 sn65dsi86_out_boe: endpoint@c4 {
> > > > > >                     remote-endpoint = <&boe_panel_in_edp>;
> > > > > >                 };
> > > > > >
> > > > > >                 sn65dsi86_out_ivo: endpoint@c5 {
> > > > > >                     remote-endpoint = <&ivo_panel_in_edp>;
> > > > > >                 };
> > > > > >             };
> > > > > >         };
> > > > > >     };
> > > > > >
> > > > > > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > > > > > ---
> > > > > >  .../bindings/display/panel/panel-common.yaml  | 26 +++++++++++++++++++
> > > > > >  1 file changed, 26 insertions(+)
> > > > > >
> > > > > > diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > > index ef8d8cdfcede..6113319b91dd 100644
> > > > > > --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > > +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> > > > > > @@ -75,6 +75,32 @@ properties:
> > > > > >        in the device graph bindings defined in
> > > > > >        Documentation/devicetree/bindings/graph.txt.
> > > > > >
> > > > > > +  panel-id:
> > > > > > +    description:
> > > > > > +      To support the case where one of several different panels can be installed
> > > > > > +      on a device, the panel-id property can be used by the firmware to identify
> > > > > > +      which panel should have it's status changed to "ok".  This property is not
> > > > > > +      used by the HLOS itself.
> > > > >
> > > > > If your firmware can modify the status property of a panel, it can also
> > > > > add DT nodes. As discussed before, I don't think this belongs to DT.
> > > > > Even if panel-id isn't used by the operating system, you have Linux
> > > > > kernel patches in this series that show that this isn't transparent.
> > > >
> > > > I've already explained several times why this is not feasible.  It
> > > > would require DtbLoader to be familiar with each individual device,
> > > > and be rev'd every time a new device appears.  That is not practical
> > > > at all.
> > > >
> > > > (And fwiw, the ACPI tables describe each panel.. with an ACPI method
> > > > that is passed the the panel-id and returns the appropriate table..
> > > > since DT doesn't have methods, this is the solution.)
> > > >
> > > > I stand by this patch, we can't keep running away from this problem
> > > > and wave the magic firmware wand.
> > >
> > > I believe in firmware solutions more than firmware magic wands :-)
> > >
> >
> > and with that in mind, I think I've come up with a firmware solution,
> > in the form of dtb overlays :-)
> >
> > I've managed to get DtbLoader to find and load a panel overlay based
> > on the panel-id it reads, which drops all patches in the patchset
> > except the last one, which now has this delta:
>
> This looks good to me. The only slight concern I have with it is
> making the overlay filename an ABI. I don't have a better suggestion
> though. How would this work for other vendors or the same panel ID
> (for different panels) used on different platforms? For different
> vendors at least, I guess dtbloader gets the base dtb path somehow and
> the overlay's are relative to that?

Not sure if "different vendors" in this context means different
OEMs/ODMs, or different SoC's?  This solution is snapdragon specific..
and in this case the panel id seems to be a flat namespace (I don't
see re-use for different panels).  But in DtbLoader I attempt loading
a device specific path first, just in case.  In particular the paths
DtbLoader uses (for dtb and panel overlay) are (where
$SysVendor/$ProductName/$BoardName come from SMBIOS tables and
$PanelId comes from a qcom specific UEFIDisplayInfo variable)
described below:

It tries to load dtb from (in order, paths relative to
EFI system partition where DtbLoader is installed):

1) \dtb\$SysVendor\$ProductName-$BoardName.dtb
2) \dtb\$SysVendor\$ProductName.dtb

and panel overlay dtb from:

1) \dtb\$SysVendor\$ProductName-$BoardName-panel-$PanelId.dtb
2) \dtb\$SysVendor\$ProductName-panel-$PanelId.dtb
3) \dtb\panels\panel-$PanelId.dtb

We are already using different dtb names for the main dtb compared to
what the kernel uses.  Which isn't great.  At some point we might want
to add SysVendor/ProductName/BoardName fields in the dtb so we could
automate renaming and stuffing the dtb's into the correct layout.

> > ---------
> > diff --git a/arch/arm64/boot/dts/qcom/Makefile
> > b/arch/arm64/boot/dts/qcom/Makefile
> > index 6498a1ec893f..1a61e8da2521 100644
> > --- a/arch/arm64/boot/dts/qcom/Makefile
> > +++ b/arch/arm64/boot/dts/qcom/Makefile
> > @@ -1,4 +1,5 @@
> >  # SPDX-License-Identifier: GPL-2.0
> > +subdir-y += panels
> >  dtb-$(CONFIG_ARCH_QCOM)    += apq8016-sbc.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)    += apq8096-db820c.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)    += ipq8074-hk01.dtb
> > diff --git a/arch/arm64/boot/dts/qcom/panels/Makefile
> > b/arch/arm64/boot/dts/qcom/panels/Makefile
> > new file mode 100644
> > index 000000000000..dbf55f423555
> > --- /dev/null
> > +++ b/arch/arm64/boot/dts/qcom/panels/Makefile
> > @@ -0,0 +1,3 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +dtb-$(CONFIG_ARCH_QCOM) += panel-c4.dtb
> > +dtb-$(CONFIG_ARCH_QCOM) += panel-c5.dtb
> > diff --git a/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> > b/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> > new file mode 100644
> > index 000000000000..ebcf65419dad
> > --- /dev/null
> > +++ b/arch/arm64/boot/dts/qcom/panels/panel-c4.dts
> > @@ -0,0 +1,17 @@
> > +// SPDX-License-Identifier: BSD-3-Clause
> > +/*
> > + * Panel overlay for panel-id 0xc4
> > + *
> > + * Copyright (c) 2019, Linaro Ltd.
> > + */
> > +
> > +/dts-v1/;
> > +/plugin/;
> > +/ {
> > +    fragment@0 {
> > +        target-path = "/panel";
> > +        __overlay__ {
> > +            compatible = "boe,nv133fhm-n61";
> > +        };
> > +    };
> > +};
> > diff --git a/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> > b/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> > new file mode 100644
> > index 000000000000..0ad5bb6003e3
> > --- /dev/null
> > +++ b/arch/arm64/boot/dts/qcom/panels/panel-c5.dts
> > @@ -0,0 +1,17 @@
> > +// SPDX-License-Identifier: BSD-3-Clause
> > +/*
> > + * Panel overlay for panel-id 0xc5
> > + *
> > + * Copyright (c) 2019, Linaro Ltd.
> > + */
> > +
> > +/dts-v1/;
> > +/plugin/;
> > +/ {
> > +    fragment@0 {
> > +        target-path = "/panel";
> > +        __overlay__ {
> > +            compatible = "ivo,m133nwf4-r0";
> > +        };
> > +    };
> > +};
> > diff --git a/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> > b/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> > index c35d8099d8eb..92c76afb721c 100644
> > --- a/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> > +++ b/arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
> > @@ -22,11 +22,13 @@
> >          hsuart0 = &uart6;
> >      };
> >
> > +    /*
> > +     * stub node which defines how panel is connected to bridge, which
> > +     * will be updated by panel specific overlay
> > +     */
> >      panel {
> > -        compatible = "ivo,m133nwf4-r0";
> >          power-supply = <&vlcm_3v3>;
> >          no-hpd;
> > -
> >          ports {
> >              port {
> >                  panel_in_edp: endpoint {
> > ---------
> >
> > Side note, try as I might, I couldn't get the 'target = <&phandle>'
> > approach to work in the overlays, so I ended up going with target-path
> > instead.  From digging thru the fdt_overlay code, I *think* it is
> > because I end up w/ an overlay dtb without symbols.  In the end, I
> > guess target-path works just as well.
>
> It's the base dtb that needs the symbols I think.
>
> BTW, to answer the question on #dri-devel, if you wanted to put the
> full panel into an overlay, the way to solve the problem of having
> bridge specific knowledge is defining a connector node. That should
> provide enough abstraction. Presumably the connector is actually the
> same across panels in this situation, so that should match up with the
> actual h/w. It could be possible to have a different physical
> connector populated for each possible panel, but hopefully that's not
> the common case.
>

ok, I'm not too familiar with this connector node thing.  I think in
the end, it is really just the compatible string that differs (ie.
power-supply, etc would all be the same for each possible panel).  But
it might be worth trying this connector node thing

BR,
-R

Patch
diff mbox series

diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
index ef8d8cdfcede..6113319b91dd 100644
--- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
+++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
@@ -75,6 +75,32 @@  properties:
       in the device graph bindings defined in
       Documentation/devicetree/bindings/graph.txt.
 
+  panel-id:
+    description:
+      To support the case where one of several different panels can be installed
+      on a device, the panel-id property can be used by the firmware to identify
+      which panel should have it's status changed to "ok".  This property is not
+      used by the HLOS itself.
+
+      For a device with multiple potential panels, a node for each potential
+      should be defined with status = "disabled", and an appropriate panel-id
+      property.  The video data producer should be setup with endpoints going to
+      each possible panel.  The firmware will find the dt node with a panel-id
+      matching the actual panel installed, and change it's status to "ok".
+
+      The exact method the firmware uses to determine the panel-id of the installed
+      panel is outside the scope of this binding, but a few examples are
+
+      1) u-boot module reading a value from a u-boot env var
+      2) EFI driver module reading a value from an EFI variable
+      3) device specific firmware reading some device specific GPIOs or
+         e-fuse
+
+      The panel-id values are an opaque integer.  They can be sparse.  The only
+      important thing is that each possible panel in the system has a unique
+      panel-id, and that the values configured in the device's DTB match the
+      values that the firmware is looking for.
+
   ddc-i2c-bus:
     $ref: /schemas/types.yaml#/definitions/phandle
     description: