diff mbox series

[RFC,1/5] dt-bindings: dma: Add CMA Heap bindings

Message ID 771534be8dfa2a3bdc3876502752f518224b9298.1738228114.git.florent.tomasin@arm.com (mailing list archive)
State New
Headers show
Series [RFC,1/5] dt-bindings: dma: Add CMA Heap bindings | expand

Commit Message

Florent Tomasin Jan. 30, 2025, 1:08 p.m. UTC 
Introduce a CMA Heap dt-binding allowing custom
CMA heap registrations.

* Note to the reviewers:
The patch was used for the development of the protected mode
feature in Panthor CSF kernel driver and is not initially thought
to land in the Linux kernel. It is mostly relevant if someone
wants to reproduce the environment of testing. Please, raise
interest if you think the patch has value in the Linux kernel.

Signed-off-by: Florent Tomasin <florent.tomasin@arm.com>
---
 .../devicetree/bindings/dma/linux,cma.yml     | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/dma/linux,cma.yml

Comments

Maxime Ripard Jan. 30, 2025, 1:28 p.m. UTC | #1 
Hi,

On Thu, Jan 30, 2025 at 01:08:57PM +0000, Florent Tomasin wrote:
> Introduce a CMA Heap dt-binding allowing custom
> CMA heap registrations.
> 
> * Note to the reviewers:
> The patch was used for the development of the protected mode
> feature in Panthor CSF kernel driver and is not initially thought
> to land in the Linux kernel. It is mostly relevant if someone
> wants to reproduce the environment of testing. Please, raise
> interest if you think the patch has value in the Linux kernel.
> 
> Signed-off-by: Florent Tomasin <florent.tomasin@arm.com>
> ---
>  .../devicetree/bindings/dma/linux,cma.yml     | 43 +++++++++++++++++++
>  1 file changed, 43 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/dma/linux,cma.yml
> 
> diff --git a/Documentation/devicetree/bindings/dma/linux,cma.yml b/Documentation/devicetree/bindings/dma/linux,cma.yml
> new file mode 100644
> index 000000000000..c532e016bbe5
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma/linux,cma.yml
> @@ -0,0 +1,43 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/dma/linux-cma.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Custom Linux CMA heap
> +
> +description:
> +  The custom Linux CMA heap device tree node allows registering
> +  of multiple CMA heaps.
> +
> +  The CMA heap name will match the node name of the "memory-region".
> +
> +properties:
> +  compatible:
> +    enum:
> +      - linux,cma
> +
> +  memory-region:
> +    maxItems: 1
> +    description: |
> +      Phandle to the reserved memory node associated with the CMA Heap.
> +      The reserved memory node must follow this binding convention:
> +       - Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> +
> +examples:
> +  - |
> +    reserved-memory {
> +      #address-cells = <2>;
> +      #size-cells = <2>;
> +
> +      custom_cma_heap: custom-cma-heap {
> +        compatible = "shared-dma-pool";
> +        reg = <0x0 0x90600000 0x0 0x1000000>;
> +        reusable;
> +      };
> +    };
> +
> +    device_cma_heap: device-cma-heap {
> +      compatible = "linux,cma";
> +      memory-region = <&custom_cma_heap>;
> +    };

Isn't it redundant with the linux,cma-default shared-dma-pool property
already?

Maxime
Rob Herring Jan. 30, 2025, 11:20 p.m. UTC | #2 
On Thu, Jan 30, 2025 at 01:08:57PM +0000, Florent Tomasin wrote:
> Introduce a CMA Heap dt-binding allowing custom
> CMA heap registrations.
> 
> * Note to the reviewers:
> The patch was used for the development of the protected mode
> feature in Panthor CSF kernel driver and is not initially thought
> to land in the Linux kernel. It is mostly relevant if someone
> wants to reproduce the environment of testing. Please, raise
> interest if you think the patch has value in the Linux kernel.

Why would panthor need CMA, it has an MMU.

In any case, I agree with Maxime that this is redundant.

Rob
Florent Tomasin Feb. 3, 2025, 1:36 p.m. UTC | #3 
On 30/01/2025 13:28, Maxime Ripard wrote:
> Hi,
> 
> On Thu, Jan 30, 2025 at 01:08:57PM +0000, Florent Tomasin wrote:
>> Introduce a CMA Heap dt-binding allowing custom
>> CMA heap registrations.
>>
>> * Note to the reviewers:
>> The patch was used for the development of the protected mode
>> feature in Panthor CSF kernel driver and is not initially thought
>> to land in the Linux kernel. It is mostly relevant if someone
>> wants to reproduce the environment of testing. Please, raise
>> interest if you think the patch has value in the Linux kernel.
>>
>> Signed-off-by: Florent Tomasin <florent.tomasin@arm.com>
>> ---
>>  .../devicetree/bindings/dma/linux,cma.yml     | 43 +++++++++++++++++++
>>  1 file changed, 43 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/dma/linux,cma.yml
>>
>> diff --git a/Documentation/devicetree/bindings/dma/linux,cma.yml b/Documentation/devicetree/bindings/dma/linux,cma.yml
>> new file mode 100644
>> index 000000000000..c532e016bbe5
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/dma/linux,cma.yml
>> @@ -0,0 +1,43 @@
>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/dma/linux-cma.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Custom Linux CMA heap
>> +
>> +description:
>> +  The custom Linux CMA heap device tree node allows registering
>> +  of multiple CMA heaps.
>> +
>> +  The CMA heap name will match the node name of the "memory-region".
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - linux,cma
>> +
>> +  memory-region:
>> +    maxItems: 1
>> +    description: |
>> +      Phandle to the reserved memory node associated with the CMA Heap.
>> +      The reserved memory node must follow this binding convention:
>> +       - Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
>> +
>> +examples:
>> +  - |
>> +    reserved-memory {
>> +      #address-cells = <2>;
>> +      #size-cells = <2>;
>> +
>> +      custom_cma_heap: custom-cma-heap {
>> +        compatible = "shared-dma-pool";
>> +        reg = <0x0 0x90600000 0x0 0x1000000>;
>> +        reusable;
>> +      };
>> +    };
>> +
>> +    device_cma_heap: device-cma-heap {
>> +      compatible = "linux,cma";
>> +      memory-region = <&custom_cma_heap>;
>> +    };
> 
> Isn't it redundant with the linux,cma-default shared-dma-pool property
> already?
> 
> Maxime

Hi Maxime,

Please correct me if my understanding is wrong,

The existing properties: linux,cma-default and shared-dma-pool, do not
allow the creations of multiple standalone CMA heaps, those will create
a single CMA heap: `dma_contiguous_default_area`? Other CMA heaps will
be bound to a driver.

I introduced the "linux,cma" to allow creating multiple standalone CMA
heaps, with the intention of validating the protected mode support on
Mali CSG GPUs. It was included in the RFC in there are interests in
this approach.

Since the Panthor CSF kernel driver does not own or manage a heap,
I needed a way to create a standalone heap. The idea here is for the
kernel driver to be an importer. I relied on a patch series to retrieve
the heap and allocate a DMA buffer from it:
- dma_heap_find()
- dma_heap_buffer_alloc()
- dma_heap_put()

Ref:
https://lore.kernel.org/lkml/20230911023038.30649-1-yong.wu@mediatek.com/#t


Since the protected/secure memory management is integration specific,
I needed a generic way for Panthor to allocate from such heap.

In some scenarios it might be a carved-out memory, in others a FW will
reside in the system (TEE) and require a secure heap driver to allocate
memory (e.g: a similar approach is followd by MTK). Such driver would
implement the allocation and free logic.

Florent
Florent Tomasin Feb. 3, 2025, 4:18 p.m. UTC | #4 
Hi Rob

On 30/01/2025 23:20, Rob Herring wrote:
> 
> Why would panthor need CMA, it has an MMU.
> 
> In any case, I agree with Maxime that this is redundant.
> 

This is correct, the GPU has an MMU. The reason I introduced this custom
CMA DTB entry is to allow creation of a standalone DMA heap which can be
retrieved by Panthor using the API exposed by:
-
https://lore.kernel.org/lkml/20230911023038.30649-1-yong.wu@mediatek.com/#t

My understanding might be wrong, I am under the impression that current
CMA driver only has `dma_contiguous_default_area` as standalone
carved-out heap and we cannot have more than one. Please correct me if
this is invalid.

With the DMA Heap API I based the RFC on, Panthor kernel driver does not
manage the protected heap itself, it relies on an exporter to do it. On
some system the secure heap will communicate with a secure FW, on others
it will be a carved-out memory with restricted access. This is
integration specific. Panthor kernel driver will expect to import a DMA
buffer obtained from a heap.

For the development of the protected mode feature, I decided to modify
the CMA driver to create a standalone DMA heap and allocate a DMA buffer
from it. It helped me abstract the importing of a heap in Panthor kernel
driver. Someone may use a different heap driver to reproduce the setup.

* Additional information to help with the context:
Mali CSF GPU requires protected memory at the device level which does
not belong to a user space process in order to allow the FW to enter
protected mode. There is a single FW per GPU instance and the FW is
loaded a probe time.

Regards,
Florent
diff mbox series

Patch

diff --git a/Documentation/devicetree/bindings/dma/linux,cma.yml b/Documentation/devicetree/bindings/dma/linux,cma.yml
new file mode 100644
index 000000000000..c532e016bbe5
--- /dev/null
+++ b/Documentation/devicetree/bindings/dma/linux,cma.yml
@@ -0,0 +1,43 @@ 
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/dma/linux-cma.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Custom Linux CMA heap
+
+description:
+  The custom Linux CMA heap device tree node allows registering
+  of multiple CMA heaps.
+
+  The CMA heap name will match the node name of the "memory-region".
+
+properties:
+  compatible:
+    enum:
+      - linux,cma
+
+  memory-region:
+    maxItems: 1
+    description: |
+      Phandle to the reserved memory node associated with the CMA Heap.
+      The reserved memory node must follow this binding convention:
+       - Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
+
+examples:
+  - |
+    reserved-memory {
+      #address-cells = <2>;
+      #size-cells = <2>;
+
+      custom_cma_heap: custom-cma-heap {
+        compatible = "shared-dma-pool";
+        reg = <0x0 0x90600000 0x0 0x1000000>;
+        reusable;
+      };
+    };
+
+    device_cma_heap: device-cma-heap {
+      compatible = "linux,cma";
+      memory-region = <&custom_cma_heap>;
+    };