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

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Message-ID: <83f88dd5-8c74-4c2f-b94e-6c16dcbd44f1@kernel.org>
Date: Tue, 1 Jul 2025 11:30:53 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 Sarthak Garg <quic_sartgarg@...cinc.com>,
 Ulf Hansson <ulf.hansson@...aro.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>,
 Adrian Hunter <adrian.hunter@...el.com>
Cc: linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 quic_cang@...cinc.com, quic_nguyenb@...cinc.com, quic_rampraka@...cinc.com,
 quic_pragalla@...cinc.com, quic_sayalil@...cinc.com,
 quic_nitirawa@...cinc.com, quic_bhaskarv@...cinc.com, kernel@....qualcomm.com
Subject: Re: [PATCH V3 2/4] dt-bindings: mmc: controller: Add
 max-sd-hs-frequency property

On 01/07/2025 11:04, Konrad Dybcio wrote:
>>>>>
>>>>> 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)


This should be clearly explained in commit msg and the DTS patch
re-written because it seems it is not a property of the SoC.

I mean, really, that last patch here makes entire discussion pointless,
because till it is in the patchset is a proof this is a SoC level property.

Best regards,
Krzysztof