[PATCH] dt-bindings: PCI: pci-ep: Add ref-clk-mode

[Niklas Cassel <cassel@kernel.org>]

While some boards designs support multiple reference clocking schemes
(e.g. Common Clock and SRNS), and can choose the clocking scheme using
e.g. a DIP switch, most boards designs only support a single clocking
scheme (even if the SoC might support multiple clocking schemes).

This property is needed such that the PCI controller driver, in endpoint
mode, can set the proper bits, e.g. the Common Clock Configuration bit and
the SRIS Clocking bit, in the PCIe Link Control Register (Offset 10h).
(Sometimes, there are also specific bits that needs to be set in the PHY.)

Some device tree bindings have already implemented vendor specific
properties to handle this, e.g. "nvidia,enable-ext-refclk" (Common Clock)
and "nvidia,enable-srns" (SRNS). However, since this property is common
for all PCI controllers running in endpoint mode, this really ought to be
a property in the common pcie-ep.yaml device tree binding.

Add a new ref-clk-mode property that describes the reference clocking
scheme used by the endpoint. (We do not add a common-clk-ssc option, since
we cannot know/control if the common clock provided by the host uses SSC.)

Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 Documentation/devicetree/bindings/pci/pci-ep.yaml | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/devicetree/bindings/pci/pci-ep.yaml b/Documentation/devicetree/bindings/pci/pci-ep.yaml
index f75000e3093d..206c1dc2ab82 100644
--- a/Documentation/devicetree/bindings/pci/pci-ep.yaml
+++ b/Documentation/devicetree/bindings/pci/pci-ep.yaml
@@ -42,6 +42,15 @@ properties:
     default: 1
     maximum: 16
 
+  ref-clk-mode:
+    description: Reference clocking architechture
+    enum:
+      - common-clk        # Common Reference Clock (provided by RC side)
+      - common-clk-ep     # Common Reference Clock (provided by EP side)
+      - common-clk-ep-ssc # Common Reference Clock With Spread (provided by EP side)
+      - srns              # Separate Reference Clocks No Spread
+      - sris              # Separate Reference Clocks Independent Spread
+
   linux,pci-domain:
     description:
       If present this property assigns a fixed PCI domain number to a PCI
-- 
2.49.0