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@xxxxxx>
> Signed-off-by: Brad Mouring <brad.mouring@xxxxxx>
> Signed-off-by: Erick Shepherd <erick.shepherd@xxxxxx>
Acked-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> ---
> 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);
