[3/6] dt-bindings: Add 'slot-power-limit-milliwatt' PCIe port property

Commit Message

Pali Rohár Feb. 22, 2022, 4:31 p.m. UTC

This property specifies slot power limit in mW unit. It is a form-factor
and board specific value and must be initialized by hardware.

Some PCIe controllers delegate this work to software to allow hardware
flexibility and therefore this property basically specifies what should
host bridge program into PCIe Slot Capabilities registers.

The property needs to be specified in mW unit instead of the special format
defined by Slot Capabilities (which encodes scaling factor or different
unit). Host drivers should convert the value from mW to needed format.

Signed-off-by: Pali Rohár <[e-mail]>
Signed-off-by: Marek Behún <[e-mail]>

---
This change was already accepted into dt-schema repo by Rob Herring:
https://github.com/devicetree-org/dt-schema/pull/66
---
 Documentation/devicetree/bindings/pci/pci.txt | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Marek Behún Feb. 22, 2022, 5:24 p.m. UTC | #1

On Tue, 22 Feb 2022 17:31:55 +0100
Pali Rohár <[e-mail]> wrote:

> This property specifies slot power limit in mW unit. It is a form-factor
> and board specific value and must be initialized by hardware.
> 
> Some PCIe controllers delegate this work to software to allow hardware
> flexibility and therefore this property basically specifies what should
> host bridge program into PCIe Slot Capabilities registers.
> 
> The property needs to be specified in mW unit instead of the special format
> defined by Slot Capabilities (which encodes scaling factor or different
> unit). Host drivers should convert the value from mW to needed format.
> 
> Signed-off-by: Pali Rohár <[e-mail]>
> Signed-off-by: Marek Behún <[e-mail]>

This patch is not needed, the property already is described in
dtschema.

Marek

Pali Rohár Feb. 22, 2022, 5:53 p.m. UTC | #2

On Tuesday 22 February 2022 18:24:15 Marek Behún wrote:
> On Tue, 22 Feb 2022 17:31:55 +0100
> Pali Rohár <[e-mail]> wrote:
> 
> > This property specifies slot power limit in mW unit. It is a form-factor
> > and board specific value and must be initialized by hardware.
> > 
> > Some PCIe controllers delegate this work to software to allow hardware
> > flexibility and therefore this property basically specifies what should
> > host bridge program into PCIe Slot Capabilities registers.
> > 
> > The property needs to be specified in mW unit instead of the special format
> > defined by Slot Capabilities (which encodes scaling factor or different
> > unit). Host drivers should convert the value from mW to needed format.
> > 
> > Signed-off-by: Pali Rohár <[e-mail]>
> > Signed-off-by: Marek Behún <[e-mail]>
> 
> This patch is not needed, the property already is described in
> dtschema.

But dtschema with this property is not included in kernel and this file
is the only in-kernel documentation. So updating it makes sense.

Patch

diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
index 6a8f2874a24d..b0cc133ed00d 100644
--- a/Documentation/devicetree/bindings/pci/pci.txt
+++ b/Documentation/devicetree/bindings/pci/pci.txt
@@ -32,6 +32,12 @@  driver implementation may support the following properties:
    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.
+- slot-power-limit-milliwatt:
+   If present, this property specifies slot power limit in milliwatts. Host
+   drivers can parse this property and use it for programming Root Port or host
+   bridge, or for composing and sending PCIe Set_Slot_Power_Limit messages
+   through the Root Port or host bridge when transitioning PCIe link from a
+   non-DL_Up Status to a DL_Up Status.
 
 PCI-PCI Bridge properties
 -------------------------