linux-kernel - Re: [PATCH] mmc: sdhci: Disable SD card clock before changing parameters

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Message-ID: <CAPDyKForSFLar9i+XJzp35ACTfBsASfnzwp4hYcYamVoRbc3Lw@mail.gmail.com>
Date: Wed, 12 Mar 2025 12:24:11 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Erick Shepherd <erick.shepherd@...com>
Cc: linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org, 
	adrian.hunter@...el.com, gratian.crisan@...rson.com, 
	Kyle Roeschley <kyle.roeschley@...com>, Brad Mouring <brad.mouring@...com>
Subject: Re: [PATCH] mmc: sdhci: Disable SD card clock before changing parameters

On Tue, 11 Feb 2025 at 22:47, Erick Shepherd <erick.shepherd@...com> wrote:
>
> Per the SD Host Controller Simplified Specification v4.20 §3.2.3, change
> the SD card clock parameters only after first disabling the external card
> clock. Doing this fixes a spurious clock pulse on Baytrail and Apollo Lake
> SD controllers which otherwise breaks voltage switching with a specific
> Swissbit SD card.
>
> Signed-off-by: Kyle Roeschley <kyle.roeschley@...com>
> Signed-off-by: Brad Mouring <brad.mouring@...com>
> Signed-off-by: Erick Shepherd <erick.shepherd@...com>

Applied for next, thanks!

Kind regards
Uffe


> ---
>  drivers/mmc/host/sdhci.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index f4a7733a8ad2..5f91b44891f9 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -2065,10 +2065,15 @@ void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
>
>         host->mmc->actual_clock = 0;
>
> -       sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
> +       clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
> +       if (clk & SDHCI_CLOCK_CARD_EN)
> +               sdhci_writew(host, clk & ~SDHCI_CLOCK_CARD_EN,
> +                       SDHCI_CLOCK_CONTROL);
>
> -       if (clock == 0)
> +       if (clock == 0) {
> +               sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
>                 return;
> +       }
>
>         clk = sdhci_calc_clk(host, clock, &host->mmc->actual_clock);
>         sdhci_enable_clk(host, clk);
> --
> 2.43.0
>