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

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Date:   Thu, 6 Apr 2023 17:39:02 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
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

Hi Jim,

Am 06.04.23 um 14:46 schrieb Jim Quinlan:
> 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#

not sure about this, but maybe we should avoid references to Linux 
kernel config parameter in a DT binding. Since the driver already gaves 
warning in case the DT parameter is present, but kernel config doesn't 
fit, this should be enough.

> +      assertion to clock active must be within 400ns.
> +    type: boolean
> +
> +  brcm,completion-timeout-msecs:
> +    description: Number of msecs before completion timeout
> +      abort occurs.
> +    $ref: /schemas/types.yaml#/definitions/uint32

According to the driver at least 0 is not allowed, maybe we should 
define minimum and maximum here and let dtbs_check take care of invalid 
values?

Best regards

> +
>     brcm,scb-sizes:
>       description: u64 giving the 64bit PCIe memory
>         viewport size of a memory controller.  There may be up to