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

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Message-ID: <168211049118.1749998.10567032742795047284.robh@kernel.org>
Date:   Fri, 21 Apr 2023 15:54:51 -0500
From:   Rob Herring <robh@...nel.org>
To:     Jim Quinlan <jim2101024@...il.com>
Cc:     linux-rpi-kernel@...ts.infradead.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Phil Elwell <phil@...pberrypi.com>, james.quinlan@...adcom.com,
        Cyril Brulebois <kibi@...ian.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v3 1/3] dt-bindings: PCI: brcmstb:
 brcm,{enable-l1ss,completion-timeout-us} props


On Wed, 19 Apr 2023 12:57:18 -0400, Jim Quinlan wrote:
> 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(+)
> 

Reviewed-by: Rob Herring <robh@...nel.org>