Thread (20 messages) 20 messages, 5 authors, 2025-09-05

Re: [PATCH V5 4/4] arm64: dts: qcom: sm8550: Add max-sd-hs-hz property

From: Krzysztof Kozlowski <krzk@kernel.org>
Date: 2025-09-04 10:52:38
Also in: linux-arm-msm, linux-mmc, lkml

On 04/09/2025 12:51, Krzysztof Kozlowski wrote:
On 04/09/2025 10:36, Konrad Dybcio wrote:
quoted
On 9/3/25 10:21 AM, 'Krzysztof Kozlowski' via kernel wrote:
quoted
On 03/09/2025 10:04, Sarthak Garg wrote:
quoted
Due to board-specific hardware constraints particularly related
to level shifter in this case the maximum frequency for SD High-Speed
(HS) mode must be limited to 37.5 MHz to ensure reliable operation of SD
card in HS mode.

This is achieved by introducing the `max-sd-hs-hz` property in the
device tree, allowing the controller to operate within safe frequency
limits for HS mode.
Probably we will now replicate the same discussion... And it will be
happening every time you send the same and not reflect it in commit msg.
Just to emphasize this - it will happen EVERY time.
quoted
quoted
Bindings say board setup, this commit msg says board config, but the
patch says SoC. This is not correct.
Both are correct, looking at the problem from two perspectives.

The bindings description mentions board-specific limitations (e.g. because
"the board's electrical design does not allow one to achieve the full rated
frequency that the SoC can otherwise do, in a stable way")

Here the author tries to argue that almost all SM8550 boards are broken
in this sense, because the reference design did not feature the required
passive components, making most (derivative) designs sort of "broken by
default" - and only some (if any?) vendors decided to go with the
additional components required to lift this limitation.

This in turn makes it fair to assume the developer experience would benefit
from having the SD card high speed modes always work (with the slight speed
cap which may not be required for the 1 or 2 designs that took the extra
step) without each board DT creator having to track down this property
separately.
And then if you send same v3, I will ask the same. Can the author
v3 -> v6
finally write commit msgs reflecting discussions and previous disagreements?
Best regards,
Krzysztof
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