linux-kernel - [PATCH v2 1/3] dt-bindings: PCI: brcmstb: Add two optional props

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Date:   Tue, 11 Apr 2023 12:59:16 -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-arm-kernel@...ts.infradead.org (moderated list:BROADCOM BCM7XXX
        ARM ARCHITECTURE),
        linux-rpi-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 v2 1/3] dt-bindings: PCI: brcmstb: Add two optional props

Regarding "brcm,enable-l1ss":

  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).  Further, the
  HW may cause a CPU abort on boot if guesses wrong regarding the need for
  (c).  So we introduce the boolean "brcm,enable-l1ss" property to indicate
  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 will follow adds more details and
  discerns between (a) and (b).

Regarding "brcm,completion-timeout-us"

  Our HW will cause a CPU abort if the L1SS exit time is longer than the
  PCIe transaction completion abort timeout.  We've been asked to make this
  configurable, so we are introducing "brcm,completion-timeout-us".

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..f7fc2f6561bb 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.  Note that when
+      in this mode, this particular HW may not meet the requirement
+      that requires CLKREQ# assertion to clock active to be
+      within 400ns.
+    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