linux-kernel - [PATCH v4] schemas: pci: Document PCIe T_POWER

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Message-Id: <20260205093346.667898-1-krishna.chundru@oss.qualcomm.com>
Date: Thu,  5 Feb 2026 15:03:46 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: andersson@...nel.org, robh@...nel.org, mani@...nel.org, krzk@...nel.org,
        helgaas@...nel.org
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        lpieralisi@...nel.org, kw@...ux.com, conor+dt@...nel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree-spec@...r.kernel.org, krishna.chundru@....qualcomm.com,
        lukas@...ner.de
Subject: [PATCH v4] schemas: pci: Document PCIe T_POWER_ON

>From PCIe r7, sec 5.5.4 & Table 5-11 in sec 5.5.5 T_POWER_ON is the
minimum amount of time (in us) that each component must wait in L1.2.Exit
after sampling CLKREQ# asserted before actively driving the interface to
ensure no device is ever actively driving into an unpowered component and
these values are based on the components and AC coupling capacitors used
in the connection linking the two components.

This property should be used to indicate the T_POWER_ON and drivers using
this property are responsible for programming both the scale and the value
of T_POWER_ON to comply with the PCIe specification.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Acked-by: Manivannan Sadhasivam <mani@...nel.org>
---
Changes in V3.
- Couple of nits from Mani & Bjorn.
- Link to v3: https://lore.kernel.org/all/20251126103112.838549-1-krishna.chundru@oss.qualcomm.com/
Changes in v2:
- Move the property to pci-device.yaml so that it will be applicable to
  endpoint devices also (Mani).
- Use latest spec (Lukas)
- Link to v2: https://lore.kernel.org/all/20251110112947.2071036-1-krishna.chundru@oss.qualcomm.com/
Changes in v1:
- Updated the commiit text (Mani).
- Link to v1: https://lore.kernel.org/all/20251110112550.2070659-1-krishna.chundru@oss.qualcomm.com/#t

 dtschema/schemas/pci/pci-device.yaml | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/dtschema/schemas/pci/pci-device.yaml b/dtschema/schemas/pci/pci-device.yaml
index ca094a0..a847500 100644
--- a/dtschema/schemas/pci/pci-device.yaml
+++ b/dtschema/schemas/pci/pci-device.yaml
@@ -63,6 +63,15 @@ properties:
     description: GPIO controlled connection to WAKE# signal
     maxItems: 1
 
+  t-power-on-us:
+    description:
+      The minimum amount of time that each component must wait in
+      L1.2.Exit after sampling CLKREQ# asserted before actively driving
+      the interface to ensure no device is ever actively driving into an
+      unpowered component. This value is based on the components and AC
+      coupling capacitors used in the connection linking the two
+      components (PCIe r7.0, sec 5.5.4).
+
 required:
   - reg
 
-- 
2.34.1