[PATCH v1] mmc: sd: fix redundant 1.8V voltage switch on cold boot with UHS card

[Kathpalia, Tanmay]

Hi All,

Friendly ping on the patch below - it has been about a month with
no feedback. Would appreciate any review at your earliest
convenience.

Thanks,
Tanmay

On 5/15/2026 12:24 AM, Tanmay Kathpalia wrote:
> When a UHS card successfully negotiates 1.8V signaling during normal
> initialization, the host voltage switch is performed as part of the
> ACMD41 handshake. Without this fix, the warm-reboot recovery path
> would fire again immediately after, switching the host voltage a
> second time unnecessarily.
>
> Add a check so the recovery path is only entered when the voltage
> switch was not already performed during the current initialization
> session.
>
> Fixes: 906ee6785b1c ("mmc: sd: Handle UHS-I voltage signaling without power cycle")
> Signed-off-by: Tanmay Kathpalia <tanmay.kathpalia at altera.com>
> ---
>   drivers/mmc/mmc.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
> index 7dadff27abe..10d8a37d2a8 100644
> --- a/drivers/mmc/mmc.c
> +++ b/drivers/mmc/mmc.c
> @@ -2720,10 +2720,11 @@ static int mmc_startup(struct mmc *mmc)
>   
>   #if CONFIG_IS_ENABLED(MMC_UHS_SUPPORT)
>   		/*
> -		 * If the card has already switched to 1.8V signaling, then
> -		 * set the signal voltage to 1.8V.
> +		 * If voltage switch was skipped during ACMD41 but the card is
> +		 * already at 1.8V (retained from a previous session, e.g. warm
> +		 * reboot), re-configure the host to match.
>   		 */
> -		if (mmc_sd_card_using_v18(mmc)) {
> +		if (!(mmc->ocr & OCR_S18R) && mmc_sd_card_using_v18(mmc)) {
>   			/*
>   			 * During a signal voltage level switch, the clock must be gated
>   			 * for 5 ms according to the SD spec.