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

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Message-Id: <20220222163158.1666-4-pali@kernel.org>
Date:   Tue, 22 Feb 2022 17:31:55 +0100
From:   Pali Rohár <pali@...nel.org>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Marek Behún <kabel@...nel.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Gregory Clement <gregory.clement@...tlin.com>
Cc:     linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/6] dt-bindings: Add 'slot-power-limit-milliwatt' PCIe port property

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 <pali@...nel.org>
Signed-off-by: Marek Behún <kabel@...nel.org>

---
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(+)

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
 -------------------------
-- 
2.20.1