linux-kernel - Re: [PATCH 4/4] ARM: dts: Fix-up EMMC2 controller's frequency

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Message-ID: <401100ea-90ad-57b1-50da-967118a090da@i2se.com>
Date:   Wed, 24 Mar 2021 16:16:00 +0100
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Nicolas Saenz Julienne <nsaenz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mmc@...r.kernel.org,
        devicetree@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     f.fainelli@...il.com, phil@...pberrypi.com,
        tim.gover@...pberrypi.com, adrian.hunter@...el.com,
        sbranden@...adcom.com, alcooperx@...il.com,
        linux-kernel@...r.kernel.org, ulf.hansson@...aro.org
Subject: Re: [PATCH 4/4] ARM: dts: Fix-up EMMC2 controller's frequency

Hi Nicolas,

Am 22.03.21 um 19:58 schrieb Nicolas Saenz Julienne:
> From: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
>
> Force emmc2's frequency to 150MHz as the default 100MHz (set by FW)
> seems to interfere with the VPU clock when setup at frequencies bigger
> than 500MHz (a pretty common case). This ends up causing unwarranted
> SDHCI CMD hangs  when no SD card is present.
>
> Signed-off-by: Nicolas Saenz Julienne <nsaenz@...nel.org>
> ---
>  arch/arm/boot/dts/bcm2711-rpi-4-b.dts | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> index 3b4ab947492a..9aa8408d9960 100644
> --- a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> +++ b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> @@ -257,6 +257,12 @@ &emmc2 {
>  	vqmmc-supply = <&sd_io_1v8_reg>;
>  	vmmc-supply = <&sd_vcc_reg>;
>  	broken-cd;
> +	/*
> +	 * Force the frequency to 150MHz as the default 100MHz seems to
> +	 * interfere with the VPU clock when setup at frequencies bigger than
> +	 * 500MHz, causing unwarranted CMD hangs.
> +	 */
> +	clock-frequency = <150000000>;

i don't want to bike-shed here, but is there any chance to solve this in
clk-bcm2835 in a less hacky way?

Anyway thank for taking care of this.

Best regards

>  	status = "okay";
>  };
>