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

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Message-ID: <d55bd5c6-d5f8-45d8-9c6b-22e401f6a7ff@linaro.org>
Date: Wed, 14 Jan 2026 10:05:35 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Jerome Brunet <jbrunet@...libre.com>, 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>
Cc: 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 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.

Neil

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