Re: [PATCH V3 2/4] dt-bindings: mmc: controller: Add max-sd-hs-frequency property
From: Krzysztof Kozlowski <krzk@kernel.org>
Date: 2025-07-01 09:31:03
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linux-arm-msm, linux-mmc, lkml
On 01/07/2025 11:04, Konrad Dybcio wrote:
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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 thatBut 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 informationAdding 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