linux-kernel - Re: [PATCH 1/2] dt-bindings: PCI: mediatek-gen3: Add support for MT8195

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Date:   Wed, 23 Jun 2021 17:02:48 +0800
From:   Jianjun Wang <jianjun.wang@...iatek.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:     Matthias Brugger <matthias.bgg@...il.com>,
        Chen-Yu Tsai <wenst@...omium.org>,
        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 Tue, 2021-06-22 at 12:05 +0100, Lorenzo Pieralisi wrote:
> 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 ?

Yes, we will send dt-bindings with dts changes in another series,
thanks.
> 
> 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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