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Subject[PATCH V5 09/16] Documentation/devicetree: Add PCIe supports-clkreq property
Some host controllers need to know the existence of clkreq signal routing to
downstream devices to be able to advertise low power features like ASPM L1
substates. Without clkreq signal routing being present, enabling ASPM L1 sub
states might lead to downstream devices falling off the bus. Hence a new device
tree property 'supports-clkreq' is added to make such host controllers
aware of clkreq signal routing to downstream devices.

Signed-off-by: Vidya Sagar <>
Changes since [v4]:
* None

Changes since [v3]:
* Rebased on top of linux-next top of the tree

Changes since [v2]:
* None

Changes since [v1]:
* This is a new patch in v2 series

Documentation/devicetree/bindings/pci/pci.txt | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
index 92c01db610df..d132f9efeb3e 100644
--- a/Documentation/devicetree/bindings/pci/pci.txt
+++ b/Documentation/devicetree/bindings/pci/pci.txt
@@ -24,6 +24,11 @@ driver implementation may support the following properties:
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.
+- supports-clkreq:
+ If present this property specifies that CLKREQ signal routing exists from
+ root port to downstream device and host bridge drivers can do programming
+ which depends on CLKREQ signal existence. For example, programming root port
+ not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.

PCI-PCI Bridge properties
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