On 02/09/2025 12:01, Dmitry Baryshkov wrote:
> On Tue, Sep 02, 2025 at 08:04:54AM +0200, Krzysztof Kozlowski wrote:
>> On 02/09/2025 06:03, Dmitry Baryshkov wrote:
>>> On Mon, Sep 01, 2025 at 05:45:49AM +0200, Krzysztof Kozlowski wrote:
>>>> On Fri, Aug 29, 2025 at 01:48:15AM +0300, Dmitry Baryshkov wrote:
>>>>> The SM6350 doesn't have MST support, as such it is not compatible with
>>>>> the SM8350 platform. Add new entry for SM6350 with fallback to SC7180
>>>>> (which belongs to the same generation and also doesn't have MST
>>>>> support).
>>>>>
>>>>> Fixes: 39086151593a ("dt-bindings: display: msm: dp-controller: document
>>>>> SM6350 compatible")
>>>>> Signed-off-by: Dmitry Baryshkov <[email protected]>
>>>>> ---
>>>>> .../devicetree/bindings/display/msm/dp-controller.yaml | 14
>>>>> +++++++++++++-
>>>>> 1 file changed, 13 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git
>>>>> a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
>>>>> b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
>>>>> index
>>>>> aed3bafa67e3c24d2a876acd29660378b367603a..0f814aa6f51406fdbdd7386027f88dfbacb24392
>>>>> 100644
>>>>> --- a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
>>>>> +++ b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
>>>>> @@ -31,13 +31,25 @@ properties:
>>>>> - qcom,sm8650-dp
>>>>> - items:
>>>>> - enum:
>>>>> - - qcom,sar2130p-dp
>>>>> - qcom,sm6350-dp
>>>>> + - const: qcom,sc7180-dp
>>>>> +
>>>>> + # deprecated entry for compatibility with old DT
>>>>> + - items:
>>>>> + - enum:
>>>>> + - qcom,sm6350-dp
>>>>> + - const: qcom,sm8350-dp
>>>>> + deprecated: true
>>>>
>>>> If it is only about bindings then there is little benefit in keeping
>>>> this, just drop this case. However you cannot drop it from DTS, so this
>>>> is a bit pointless.
>>>
>>> Our plan is:
>>> - land updated DT bindings, describing MST clocks on MST-enabled
>>> platforms,
>>> - land updated DTS, adding MST clocks where applicable,
>>
>> This part breaks all out-of-tree users of DTS.
>
> User of which one? SM6350 or all DTS?
SM6350.
>
> It extends the ABI, so no, it shouldn't. We add regions and clocks,
No, it does not extend the ABI. You are changing the fallback, so you
are changing the ABI.
> existing users can use the previously defined feature set.
>
> Anyway, is it about adding more explicit note to the cover letter and/or
> commit message or would you have any other proposal on how to handle the
> issue?
Please be explicit if Linux was working with the old fallback or not. In
the DTS change be explicit about impact, e.g. that sc7180 fallback is
there since forever.
>
>>
>>> - land driver changes, keeping legacy support for non-MST DTs on
>>> MST-enabled SoCs
>>>
>>>>
>>>> Lack of MST support is not informative enough to claim it is not
>>>> compatible with 8350. For example if it was working fine via fallback,
>>>> then that statement is simply not correct.
>>>>
>>>> And it HAD to work fine, because there is nothing binding to
>>>> qcom,sm6350-dp.
>>>
>>> It is working fine since currently we don't have MST support on the
>>> driver side (nor do we describe MST clocks in DT). It's true that the
>>> driver will have to handle non-MST DT for SM8350. However I definitely
>>> don't want to describe both cases in the bindings. SM6350 is not going
>>> to be compatible with the MST-enabled SM8350 schema.
>>
>> The question is rather: is SM6350 going to be compatible (working) with
>> MST-enabled drivers.
>
> If somebody implements e.g. U-Boot DP MST support after we land DP MST
> bindings, I would not guarantee that. SM8350 will already have second
> stream clock.
Having second stream clock does not mean device stops working with Linux
kernel. I can easily imagine both cases after adding MST to the drivers,
the SM6350 stops working or keeps working...
Best regards,
Krzysztof
