Re: [PATCH V3 2/4] dt-bindings: mmc: controller: Add max-sd-hs-frequency property

[Konrad Dybcio]

On 24-Jun-25 08:06, Krzysztof Kozlowski wrote:
> On 23/06/2025 14:31, Konrad Dybcio wrote:
>> On 6/23/25 2:16 PM, Krzysztof Kozlowski wrote:
>>> On 23/06/2025 14:08, Konrad Dybcio wrote:
>>>>>>>
>>>>>>> This might be fine, but your DTS suggests clearly this is SoC compatible
>>>>>>> deducible, which I already said at v1.
>>>>>>
>>>>>> I don't understand why you're rejecting a common solution to a problem
>>>>>> that surely exists outside this one specific chip from one specific
>>>>>> vendor, which may be caused by a multitude of design choices, including
>>>>>> erratic board (not SoC) electrical design
>>>>>
>>>>> No one brought any arguments so far that common solution is needed. The
>>>>> only argument provided - sm8550 - is showing this is soc design.
>>>>>
>>>>> I don't reject common solution. I provided review at v1 to which no one
>>>>> responded, no one argued, no one provided other arguments.
>>>>
>>>> Okay, so the specific problem that causes this observable limitation
>>>> exists on SM8550 and at least one more platform which is not upstream
>>>> today. It can be caused by various electrical issues, in our specific
>>>> case by something internal to the SoC (but external factors may apply
>>>> too)
>>>>
>>>> Looking at the docs, a number of platforms have various limitations
>>>> with regards to frequency at specific speed-modes, some of which seem
>>>> to be handled implicitly by rounding in the clock framework's
>>>> round/set_rate().
>>>>
>>>> I can very easily imagine there are either boards or platforms in the
>>>> wild, where the speed must be limited for various reasons, maybe some
>>>> of them currently don't advertise it (like sm8550 on next/master) to
>>>> hide that
>>>
>>> But there are no such now. The only argument (fact) provided in this
>>> patchset is: this is issue specific to SM8550 SoC, not the board. See
>>> last patch. Therefore this is compatible-deducible and this makes
>>> property without any upstream user.
>>
>> When one appears, we will have to carry code to repeat what the property
>> does, based on a specific compatible.. And all OS implementations will
>> have to do the same, instead of parsing the explicit information
> 
> Adding new property in such case will be trivial and simple, unlike
> having to maintain unused ABI.
> 
> And it will be unused, because last patch DTS should be rejected on that
> basis: adding redundant properties which are already defined by the
> compatible.

Got some more fresh information.. This apparently *does* vary across
boards, as there is a recommended hardware workaround to this rate
limitation (requiring an external clock source, which is up to the
OEM to implement or not)

Konrad