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

[Adrian Hunter <adrian.hunter@intel.com>]

On 11/02/25 23:46, Erick Shepherd 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@ni.com>
> Signed-off-by: Brad Mouring <brad.mouring@ni.com>
> Signed-off-by: Erick Shepherd <erick.shepherd@ni.com>

Acked-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
>  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);