Date:   Tue, 22 Jun 2021 12:05:17 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Matthias Brugger <matthias.bgg@...il.com>
Cc:     Chen-Yu Tsai <wenst@...omium.org>,
        Jianjun Wang <jianjun.wang@...iatek.com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>, linux-pci@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Randy Wu <Randy.Wu@...iatek.com>, youlin.pei@...iatek.com
Subject: Re: [PATCH 1/2] dt-bindings: PCI: mediatek-gen3: Add support for
 MT8195

On Wed, Jun 02, 2021 at 01:33:07PM +0200, Matthias Brugger wrote:
> 
> 
> On 01/06/2021 08:07, Chen-Yu Tsai wrote:
> > Hi,
> > 
> > On Tue, Jun 1, 2021 at 1:50 PM Jianjun Wang <jianjun.wang@...iatek.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@...iatek.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.
> > 
> 
> I agree, if no differences between the two chips are known, adding a
> binding withe new compatible and a fallback is a good thing. If we
> later on realize that mt8195 PCI block has differences, we can add the
> matching to the driver.

So this series can be dropped, right ?

Thanks,
Lorenzo

> Regards,
> Matthias
> 
> > 
> > Regards
> > ChenYu
> > 
> > 
> >> Thanks.
> >>>
> >>>
> >>> Thanks
> >>> ChenYu
> >>>
> >>>
> >>>> Signed-off-by: Jianjun Wang <jianjun.wang@...iatek.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@...ts.infradead.org
> >>>> http://lists.infradead.org/mailman/listinfo/linux-mediatek
> >>

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