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From:   Chen-Yu Tsai <wenst@chromium.org>
Date:   Tue, 1 Jun 2021 14:07:58 +0800
Message-ID: <CAGXv+5GMTbC5TTgURhPAvxBEY18S6-T-BZ9CpXsO91Trim7TXw@mail.gmail.com>
Subject: Re: [PATCH 1/2] dt-bindings: PCI: mediatek-gen3: Add support for MT8195
To:     Jianjun Wang <jianjun.wang@mediatek.com>
Cc:     Ryder Lee <ryder.lee@mediatek.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Rob Herring <robh+dt@kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        linux-pci@vger.kernel.org, linux-mediatek@lists.infradead.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Randy Wu <Randy.Wu@mediatek.com>, youlin.pei@mediatek.com
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Hi,

On Tue, Jun 1, 2021 at 1:50 PM Jianjun Wang <jianjun.wang@mediatek.com> wrote:
>
> On Tue, 2021-06-01 at 11:53 +0800, Chen-Yu Tsai wrote:
> > Hi,
> >
> > On Tue, Jun 1, 2021 at 10:50 AM Jianjun Wang <jianjun.wang@mediatek.com> wrote:
> > >
> > > MT8195 is an ARM platform SoC which has the same PCIe IP with MT8192.
> >
> > Based on what I'm seeing internally, there seems to be some inconsistency
> > across the MediaTek platform on whether new compatible strings should be
> > introduced for "fully compatible" IP blocks.
> >
> > If this hardware block in MT8195 is "the same" as the one in MT8192, do we
> > really need the new compatible string? Are there any concerns?
>
> Hi Chen-Yu,
>
> It's ok to reuse the compatible string with MT8192, but I think this
> will be easier to find which platforms this driver is compatible with,
> especially when we have more and more platforms in the future.

If it's just for informational purposes, then having the MT8192 compatible
as a fallback would work, and we wouldn't need to make changes to the driver.
This works better especially if we have to support multiple operating systems
that use device tree.

So we would want

    "mediatek,mt8195-pcie", "mediatek,mt8192-pcie"

and

    "mediatek,mt8192-pcie"

be the valid options.

Personally I'm not seeing enough value to justify adding the compatible string
just for informational purposes though. One could easily discern which hardware
is used by looking at the device tree.


Regards
ChenYu


> Thanks.
> >
> >
> > Thanks
> > ChenYu
> >
> >
> > > Signed-off-by: Jianjun Wang <jianjun.wang@mediatek.com>
> > > ---
> > >  Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml b/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> > > index e7b1f9892da4..d5e4a3e63d97 100644
> > > --- a/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> > > +++ b/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> > > @@ -48,7 +48,9 @@ allOf:
> > >
> > >  properties:
> > >    compatible:
> > > -    const: mediatek,mt8192-pcie
> > > +    oneOf:
> > > +      - const: mediatek,mt8192-pcie
> > > +      - const: mediatek,mt8195-pcie
> > >
> > >    reg:
> > >      maxItems: 1
> > > --
> > > 2.18.0
> > > _______________________________________________
> > > Linux-mediatek mailing list
> > > Linux-mediatek@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-mediatek
>