linux-kernel - Re: [PATCH v4 1/2] dt-bindings: pci: Retrain Link to work around Gen2 training defect.

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Message-ID: <912c1efa-6c25-9e5d-5094-6c9dd8e3755d@ti.com>
Date:   Mon, 14 Dec 2020 09:50:56 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Athani Nadeem Ladkhan <nadeem@...ence.com>,
        Rob Herring <robh@...nel.org>
CC:     Tom Joseph <tjoseph@...ence.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        PCI <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Milind Parab <mparab@...ence.com>,
        Swapnil Kashinath Jakhade <sjakhade@...ence.com>,
        Parshuram Raju Thombare <pthombar@...ence.com>
Subject: Re: [PATCH v4 1/2] dt-bindings: pci: Retrain Link to work around Gen2
 training defect.

Hi Nadeem,

On 12/12/20 12:37 pm, Athani Nadeem Ladkhan wrote:
> Hi Rob / Kishon,
> 
>> -----Original Message-----
>> From: Rob Herring <robh@...nel.org>
>> Sent: Friday, December 11, 2020 10:32 PM
>> To: Athani Nadeem Ladkhan <nadeem@...ence.com>
>> Cc: Tom Joseph <tjoseph@...ence.com>; Lorenzo Pieralisi
>> <lorenzo.pieralisi@....com>; Bjorn Helgaas <bhelgaas@...gle.com>; PCI
>> <linux-pci@...r.kernel.org>; linux-kernel@...r.kernel.org; Kishon Vijay
>> Abraham I <kishon@...com>; devicetree@...r.kernel.org; Milind Parab
>> <mparab@...ence.com>; Swapnil Kashinath Jakhade
>> <sjakhade@...ence.com>; Parshuram Raju Thombare
>> <pthombar@...ence.com>
>> Subject: Re: [PATCH v4 1/2] dt-bindings: pci: Retrain Link to work around
>> Gen2 training defect.
>>
>> EXTERNAL MAIL
>>
>>
>> On Fri, Dec 11, 2020 at 9:03 AM Nadeem Athani <nadeem@...ence.com>
>> wrote:
>>>
>>> Cadence controller will not initiate autonomous speed change if
>>> strapped as Gen2. The Retrain Link bit is set as quirk to enable this speed
>> change.
>>> Adding a quirk flag based on a new compatible string.
>>>
>>> Signed-off-by: Nadeem Athani <nadeem@...ence.com>
>>> ---
>>>  Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml | 4
>>> +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git
>>> a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
>>> b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
>>> index 293b8ec318bc..204d78f9efe3 100644
>>> --- a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
>>> +++ b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
>>> @@ -15,7 +15,9 @@ allOf:
>>>
>>>  properties:
>>>    compatible:
>>> -    const: cdns,cdns-pcie-host
>>> +    enum:
>>> +        - cdns,cdns-pcie-host
>>> +        - cdns,cdns-pcie-host-quirk-retrain
>>
>> So, we'll just keep adding quirk strings on to the compatible? I don't think so.
>> Compatible strings should map to a specific implementation/platform and
>> quirks can then be implied from them. This is the only way we can implement
>> quirks in the OS without firmware
>> (DT) changes.
> Ok, I will change the compatible string to " ti,j721e-pcie-host" in place of  " cdns,cdns-pcie-host-quirk-retrain" .
> @Kishon Vijay Abraham I: Is this fine? Or will you suggest an appropriate name?

IMHO it should be something like "cdns,cdns-pcie-host-vX", since the
quirk itself is not specific to TI platform rather Cadence IP version.

Thank You,
Kishon