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

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Message-ID: <5c6d0259-0fe2-4faa-5ecf-8621467533a1@gmail.com>
Date:   Thu, 6 Apr 2023 11:47:46 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Jim Quinlan <jim2101024@...il.com>,
        Stefan Wahren <stefan.wahren@...e.com>
Cc:     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,
        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 4/6/23 11:35, Krzysztof Kozlowski wrote:
> On 06/04/2023 18:58, Jim Quinlan wrote:
>> On Thu, Apr 6, 2023 at 11:39 AM Stefan Wahren <stefan.wahren@...e.com> wrote:
>>>
>>> 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.
>>
>> Hello Stefan,
>> I will remove this reference.
>>>
>>>> +      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?
>> I'm not sure I follow what you mean about a zero value;  the property
>> may have any value but the driver will clamp it
>> to a minimum of ~30msec.  Regardless, I can add a  "minimum: 30" line
>> to the YAML.
> 
> If "completion" means Linux completion, then it is not suitable for DT
> and entire property should be removed. If it is something else, then
> explain here and commit msg. So far both refer to some completion...

This is a PCIe root complex binding so completion needs to be understood 
in the context of PCIe, that is the time needed for the root complex to 
complete/finish/proceed with a PCIe transaction layer packet (TLP).
-- 
Florian