linux-kernel - [PATCH v3 1/3] dt-bindings: PCI: brcmstb: brcm,{enable-l1ss,completion-timeout-us} props

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Date:   Wed, 19 Apr 2023 12:57:18 -0400
From:   Jim Quinlan <jim2101024@...il.com>
To:     linux-pci@...r.kernel.org,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Cyril Brulebois <kibi@...ian.org>,
        Phil Elwell <phil@...pberrypi.com>,
        bcm-kernel-feedback-list@...adcom.com, jim2101024@...il.com,
        james.quinlan@...adcom.com
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-rpi-kernel@...ts.infradead.org (moderated list:BROADCOM
        BCM2711/BCM2835 ARM ARCHITECTURE),
        linux-arm-kernel@...ts.infradead.org (moderated list:BROADCOM
        BCM2711/BCM2835 ARM ARCHITECTURE),
        devicetree@...r.kernel.org (open list:OPEN FIRMWARE AND FLATTENED
        DEVICE TREE BINDINGS), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v3 1/3] dt-bindings: PCI: brcmstb: brcm,{enable-l1ss,completion-timeout-us} props

This commit introduces two new properties:

brcm,enable-l1ss (bool):

  The Broadcom STB/CM PCIe HW -- a core that is also used by RPi SOCs --
  requires the driver probe() to deliberately place the HW one of three
  CLKREQ# modes:

  (a) CLKREQ# driven by the RC unconditionally
  (b) CLKREQ# driven by the EP for ASPM L0s, L1
  (c) Bidirectional CLKREQ#, as used for L1 Substates (L1SS).

  The HW+driver can tell the difference between downstream devices that
  need (a) and (b), but does not know when to configure (c).  All devices
  should work fine when the driver chooses (a) or (b), but (c) may be
  desired to realize the extra power savings that L1SS offers.  So we
  introduce the boolean "brcm,enable-l1ss" property to inform the driver
  that (c) is desired.  Setting this property only makes sense when the
  downstream device is L1SS-capable and the OS is configured to activate
  this mode (e.g. policy==superpowersave).

  This property is already present in the Raspian version of Linux, but the
  upstream driver implementaion that follows adds more details and discerns
  between (a) and (b).

brcm,completion-timeout-us (u32):

  Our HW will cause a CPU abort on any PCI transaction completion abort
  error.  It makes sense then to increase the timeout value for this type
  of error in hopes that the response is merely delayed.  Further,
  L1SS-capable devices may have a long L1SS exit time and may require a
  custom timeout value: we've been asked by our customers to make this
  configurable for just this reason.

Signed-off-by: Jim Quinlan <jim2101024@...il.com>
---
 .../devicetree/bindings/pci/brcm,stb-pcie.yaml   | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
index 7e15aae7d69e..239cc95545bd 100644
--- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
+++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
@@ -64,6 +64,22 @@ properties:

   aspm-no-l0s: true

+  brcm,enable-l1ss:
+    description: Indicates that PCIe L1SS power savings
+      are desired, the downstream device is L1SS-capable, and the
+      OS has been configured to enable this mode.  For boards
+      using a mini-card connector, this mode may not meet the
+      TCRLon maximum time of 400ns, as specified in 3.2.5.2.5
+      of the PCI Express Mini CEM 2.0 specification.
+    type: boolean
+
+  brcm,completion-timeout-us:
+    description: Number of microseconds before PCI transaction
+      completion timeout abort is signalled.
+    minimum: 16
+    default: 1000000
+    maximum: 19884107
+
   brcm,scb-sizes:
     description: u64 giving the 64bit PCIe memory
       viewport size of a memory controller.  There may be up to
-- 
2.17.1