UPSTREAM: Documentation/devicetree: Add new property to specify the max link speed

Some of the host drivers have the requirement of knowing whether the
EP would never train at some link speed at all. For instance, on some
boards, the link won't train at 5 GT/s but the host driver still sacrifice
some cycle to wait for the resule of training at 5 GT/s as the host could
actually support 5 GT/s. So we could parse this new property and make the
host drivers be aware of these cases.

Change-Id: I7f557282462a7146d8d15af560001c81ccc7e1a7
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
(am from git.kernel.org/cgit/linux/kernel/git/next/linux-next.git
commit 2fa39159b6a9931d6fd82ecbe65357e0ad77e1a4)

diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
index 08dcfad09f8d7bdfd60e5254ef98aa42ed07a11d..e7d97a3bd17f3e2778c9a71e8d655caebf9fb35d 100644 (file)
--- a/Documentation/devicetree/bindings/pci/pci.txt
+++ b/Documentation/devicetree/bindings/pci/pci.txt
@@ -18,3 +18,9 @@ driver implementation may support the following properties:
    host bridges in the system, otherwise potentially conflicting domain numbers
    may be assigned to root buses behind different host bridges.  The domain
    number for each host bridge in the system must be unique.
    host bridges in the system, otherwise potentially conflicting domain numbers
    may be assigned to root buses behind different host bridges.  The domain
    number for each host bridge in the system must be unique.

+- max-link-speed:
+   If present this property specifies PCI gen for link capability. The host drivers
+   could add this as a strategy to avoid unnecessary operation for unsupported
+   link speed, for instance, trying to do training for unsupported link speed, etc.
+   Must be '4' for gen4, '3' for gen3, '2' for gen2, and '1' for gen1. Any other
+   values are invalid.