| Message ID | 20250404-ep-msi-v16-4-d4919d68c0d0@nxp.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | PCI: EP: Add RC-to-EP doorbell with platform MSI controller | expand |
On Fri, Apr 04, 2025 at 03:01:05PM -0400, Frank Li wrote: > Document the use of msi-map for PCI Endpoint (EP) controllers, which can > use MSI as a doorbell mechanism. Each EP controller can support up to 8 > physical functions and 65,536 virtual functions. > > Define how to construct device IDs using function bits [2:0] and virtual > function index bits [31:3], enabling msi-map to associate each child device > with a specific msi-specifier. > > Include a device tree example illustrating this configuration. > > Signed-off-by: Frank Li <Frank.Li@nxp.com> > --- > change from v15 to v16 > - new patch > --- > Documentation/devicetree/bindings/pci/pci-msi.txt | 51 +++++++++++++++++++++++ > 1 file changed, 51 insertions(+) Please don't add to .txt files. Rob
On Fri, Apr 04, 2025 at 03:11:40PM -0500, Rob Herring wrote: > On Fri, Apr 04, 2025 at 03:01:05PM -0400, Frank Li wrote: > > Document the use of msi-map for PCI Endpoint (EP) controllers, which can > > use MSI as a doorbell mechanism. Each EP controller can support up to 8 > > physical functions and 65,536 virtual functions. > > > > Define how to construct device IDs using function bits [2:0] and virtual > > function index bits [31:3], enabling msi-map to associate each child device > > with a specific msi-specifier. > > > > Include a device tree example illustrating this configuration. > > > > Signed-off-by: Frank Li <Frank.Li@nxp.com> > > --- > > change from v15 to v16 > > - new patch > > --- > > Documentation/devicetree/bindings/pci/pci-msi.txt | 51 +++++++++++++++++++++++ > > 1 file changed, 51 insertions(+) > > Please don't add to .txt files. where should put? Suggest by Marc Zyngier <maz@kernel.org> "- Documentation: the msi-map property usage is undefined outside of a PCIe RC, and the way you describe its use is so vague I read anything in it. Please update Documentation/devicetree/bindings/pci/pci-msi.txt to reflect the new use case." https://lore.kernel.org/all/86ldtpot6m.wl-maz@kernel.org/ Frank > > Rob
On Fri, Apr 04, 2025 at 04:33:00PM -0400, Frank Li wrote: > On Fri, Apr 04, 2025 at 03:11:40PM -0500, Rob Herring wrote: > > On Fri, Apr 04, 2025 at 03:01:05PM -0400, Frank Li wrote: > > > Document the use of msi-map for PCI Endpoint (EP) controllers, which can > > > use MSI as a doorbell mechanism. Each EP controller can support up to 8 > > > physical functions and 65,536 virtual functions. > > > > > > Define how to construct device IDs using function bits [2:0] and virtual > > > function index bits [31:3], enabling msi-map to associate each child device > > > with a specific msi-specifier. > > > > > > Include a device tree example illustrating this configuration. > > > > > > Signed-off-by: Frank Li <Frank.Li@nxp.com> > > > --- > > > change from v15 to v16 > > > - new patch > > > --- > > > Documentation/devicetree/bindings/pci/pci-msi.txt | 51 +++++++++++++++++++++++ > > > 1 file changed, 51 insertions(+) > > > > Please don't add to .txt files. > > where should put? Where ever you are putting the schema for msi-map for endpoints... Looks like that's nowhere currently. The endpoint side is documented in pci-ep.yaml, so there I suppose. What's in pci-msi.txt already has mostly moved to dtschema dtschema/schemas/pci/pci-host-bridge.yaml. Rob
diff --git a/Documentation/devicetree/bindings/pci/pci-msi.txt b/Documentation/devicetree/bindings/pci/pci-msi.txt index b73d839657b66..6a356707d01fc 100644 --- a/Documentation/devicetree/bindings/pci/pci-msi.txt +++ b/Documentation/devicetree/bindings/pci/pci-msi.txt @@ -218,3 +218,54 @@ Example (5) <0x0000 &msi_b 0x0000 0x10000>; }; }; + +PCI Endpoint +============ + +A PCI Endpoint (EP) can use MSI as a doorbell function. This is achieved by +mapping the MSI controller's address into PCI BAR<n>. The PCI Root Complex +can write to this BAR<n>, triggering the EP to generate IRQ. This notifies +the EP-side driver of an event, eliminating the need for the driver to +continuously poll for status changes. + +However, the EP cannot rely on Requester ID (RID) because the RID is +determined by the PCI topology of the host system. Since the EP may be +connected to different PCI hosts, the RID can vary between systems and is +therefore not a reliable identifier. + +Each EP can support up to 8 physical functions and up to 65,536 virtual +functions. To uniquely identify each child device, a device ID is defined +as + - Bits [2:0] for the function number (func) + - Bits [31:3] for the virtual function index (vfunc) + +The resulting device ID is computed as: + + (func & 0x7) | (vfunc << 3) + +msi-map can map it to an MSI controller and associated msi-specifier data. + +Example EP +========== +/ { + #address-cells = <1>; + #size-cells = <1>; + + msi: msi-controller@a { + reg = <0xa 0x1>; + compatible = "vendor,some-controller"; + msi-controller; + #msi-cells = <1>; + }; + + pci_ep: pci-ep@f { + reg = <0xf 0x1>; + compatible = "vendor,pcie-ep"; + + /* + * The sideband data provided to the MSI controller is + * the device id, function<n> maps to 0x80 + n. + */ + msi-map = <0x0 &msi_a 0x80 0x8>, + }; +};
Document the use of msi-map for PCI Endpoint (EP) controllers, which can use MSI as a doorbell mechanism. Each EP controller can support up to 8 physical functions and 65,536 virtual functions. Define how to construct device IDs using function bits [2:0] and virtual function index bits [31:3], enabling msi-map to associate each child device with a specific msi-specifier. Include a device tree example illustrating this configuration. Signed-off-by: Frank Li <Frank.Li@nxp.com> --- change from v15 to v16 - new patch --- Documentation/devicetree/bindings/pci/pci-msi.txt | 51 +++++++++++++++++++++++ 1 file changed, 51 insertions(+)