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

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Date:   Thu, 6 Apr 2023 20:54:49 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Florian Fainelli <f.fainelli@...il.com>,
        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:     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 20:53, Florian Fainelli wrote:
> On 4/6/23 11:34, Krzysztof Kozlowski wrote:
>> 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?
> 
> In other words, there should be no OS/Linux specific comments in a 
> Device Tree binding, which would be a friendlier and nicer way of 
> providing the same feedback.

I want to give also the answer also why there should be no OS/Linux
specific comments, so the reader can stop a bit and think about it :)

Best regards,
Krzysztof