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

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Message-ID: <e0e66895-e68a-4420-a61b-98a689798ce4@kernel.org>
Date: Tue, 24 Jun 2025 08:06:45 +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 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.

Best regards,
Krzysztof