linux-kernel - Re: [PATCH v2 1/2] arm64: dts: amlogic: s4: assign mmc b clock to 24MHz

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Message-ID: <1jikd4xyro.fsf@starbuckisacylon.baylibre.com>
Date: Wed, 14 Jan 2026 11:40:59 +0100
From: Jerome Brunet <jbrunet@...libre.com>
To: Neil Armstrong <neil.armstrong@...aro.org>
Cc: Rob Herring <robh@...nel.org>,  Krzysztof Kozlowski
 <krzk+dt@...nel.org>,  Conor Dooley <conor+dt@...nel.org>,  Kevin Hilman
 <khilman@...libre.com>,  Martin Blumenstingl
 <martin.blumenstingl@...glemail.com>,  Xianwei Zhao
 <xianwei.zhao@...ogic.com>,  Nick Xie <nick@...das.com>,
  devicetree@...r.kernel.org,  linux-arm-kernel@...ts.infradead.org,
  linux-amlogic@...ts.infradead.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] arm64: dts: amlogic: s4: assign mmc b clock to
 24MHz

On mer. 14 janv. 2026 at 10:05, Neil Armstrong <neil.armstrong@...aro.org> wrote:

> On 1/14/26 09:56, Jerome Brunet wrote:
>> The amlogic MMC driver operate with the assumption that MMC clock
>> is configured to provide 24MHz. It uses this path for low
>> rates such as 400kHz.
>> This assumption did hold true until but it now, but it is apparently
>> not the case with s4. The clock has been reported to provide 1GHz
>> instead. This is most likely due to how the bootloader is using the MMC
>> clock on this platform.
>> Regardless of why the MMC clock rate is 1GHz, if the MMC driver expects
>> 24MHz, the clock should be properly assigned, so assign it.
>> Reported-by: Nick Xie <nick@...das.com>
>> Closes: https://lore.kernel.org/linux-amlogic/20260113011931.40424-1-nick@khadas.com/
>> Fixes: 3ab9d54b5d84 ("arm64: dts: amlogic: enable some device nodes for S4")
>> Tested-by: Nick Xie <nick@...das.com>
>> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
>> ---
>>   arch/arm64/boot/dts/amlogic/meson-s4.dtsi | 4 ++++
>>   1 file changed, 4 insertions(+)
>> diff --git a/arch/arm64/boot/dts/amlogic/meson-s4.dtsi
>> b/arch/arm64/boot/dts/amlogic/meson-s4.dtsi
>> index 9d99ed2994df..62538fd9db6b 100644
>> --- a/arch/arm64/boot/dts/amlogic/meson-s4.dtsi
>> +++ b/arch/arm64/boot/dts/amlogic/meson-s4.dtsi
>> @@ -838,6 +838,10 @@ sd: mmc@...8a000 {
>>   			clock-names = "core", "clkin0", "clkin1";
>>   			resets = <&reset RESET_SD_EMMC_B>;
>>   			status = "disabled";
>> +
>> +			assigned-clocks = <&clkc_periphs CLKID_SD_EMMC_B>;
>> +			assigned-clock-parents = <0>;
>
> In this case, assigned-clock-parents should be dropped.
>

Dunno why I thought that was always required. I'll fix it and the other
instances

> Neil
>
>> +			assigned-clock-rates = <24000000>;
>>   		};
>>     		emmc: mmc@...8c000 {
>> 

-- 
Jerome