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

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Message-ID: <CAL_JsqLEmb4N6AKWpJmh9mGkE3QWsgABUqcH4Zvb5CiSMe_Zvg@mail.gmail.com>
Date:   Mon, 14 Dec 2020 09:05:23 -0600
From:   Rob Herring <robh@...nel.org>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Athani Nadeem Ladkhan <nadeem@...ence.com>,
        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.

On Sun, Dec 13, 2020 at 10:21 PM Kishon Vijay Abraham I <kishon@...com> wrote:
>
> 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.

That's fine if Cadence has a need for it, but for TI platforms use the
TI compatible string. ECOs on version X IP without changing X is not
uncommon.

Rob