Starting with the i.MX7, arch PCIe instance has a differential refclk pad,
which can beused in multiple ways:

- It's not used at all and the PHY reference clock is provided by a SoC
  internal source, like on the previous SOCs.
- It's used as a clock input, for the board to provide a reference clock
  for the PHY.
- It's used as a clock output, where the PHY reference clock is provided
  by a SoC internal source and the same clock is also routed to the
  refclk pad for consumption of board-level components.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
---
 Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
index 308540df99ef..3ebd8553a818 100644
--- a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt
+++ b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt

@@ -38,6 +38,11 @@ Optional properties:
   The regulator will be enabled when initializing the PCIe host and
   disabled either as part of the init process or when shutting down the
   host.
+- fsl,refclk-pad-mode: Usage mode of the refclk pad. Valid values:
+  - 0: pad not used. PHY refclock is derived from SoC internal source.
+  - 1: pad input. PHY refclock is provided externally via the refclk pad.
+  - 2: pad output. PHY refclock is derived from SoC internal source and
+       provided on the refclk pad.