linux-kernel - Re: [PATCH v1 1/3] dt-bindings: PCI: brcmstb: Add two optional props

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Message-ID: <ebde318b-53be-6779-4f0c-a614c01a0b0a@linaro.org>
Date:   Thu, 6 Apr 2023 20:34:20 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jim Quinlan <jim2101024@...il.com>, 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, 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>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/3] dt-bindings: PCI: brcmstb: Add two optional props

On 06/04/2023 14:46, Jim Quinlan wrote:
> Regarding "brcm,enable-l1ss":
> 
>   The Broadcom STB/CM PCIe HW -- which is also used by RPi SOCs -- requires
>   the driver probe to configure one of three clkreq# modes:
> 
>   (a) clkreq# driven by the RC
>   (b) clkreq# driven by the EP for ASPM L0s, L1
>   (c) bidirectional clkreq#, as used for L1 Substates (L1SS).
> 
>   The HW can tell the difference between (a) and (b), but does not know
>   when to configure (c).  Further, the HW will 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.  This
>   property is already present in the Raspian version of Linux, but the
>   driver implementaion that will follow adds more details and discerns
>   between (a) and (b).
> 
> Regarding "brcm,completion-timeout-msecs"
> 
>   Our HW will cause a CPU abort if the L1SS exit time is longer than the
>   completion abort timeout.  We've been asked to make this configurable, so
>   we are introducing "brcm,completion-abort-msecs".
> 
> Signed-off-by: Jim Quinlan <jim2101024@...il.com>
> ---
>  .../devicetree/bindings/pci/brcm,stb-pcie.yaml       | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> index 7e15aae7d69e..ef4ccc05b258 100644
> --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> @@ -64,6 +64,18 @@ properties:
>  
>    aspm-no-l0s: true
>  
> +  brcm,enable-l1ss:
> +    description: Indicates that the downstream device is L1SS
> +      capable and L1SS is desired, e.g. by setting
> +      CONFIG_PCIEASPM_POWER_SUPERSAVE=y.  Note that CLKREQ#

How does CONFIG_PCIEASPM_POWER_SUPERSAVE apply to *BSD?

> +      assertion to clock active must be within 400ns.
> +    type: boolean
> +
> +  brcm,completion-timeout-msecs:

Use standard unit suffixes.

> +    description: Number of msecs before completion timeout
> +      abort occurs.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
>    brcm,scb-sizes:
>      description: u64 giving the 64bit PCIe memory
>        viewport size of a memory controller.  There may be up to

Best regards,
Krzysztof