Date:   Wed, 2 Jun 2021 13:33:07 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Chen-Yu Tsai <wenst@...omium.org>,
        Jianjun Wang <jianjun.wang@...iatek.com>
Cc:     Ryder Lee <ryder.lee@...iatek.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        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 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.

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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