Re: [PATCH v2 1/2] mmc: core: sdio: retry without UHS if UHS init fails

[Ulf Hansson]

On Tue, Oct 27, 2026 at 1:24 PM Deomid rojer Ryabkov <rojer@xxxxxxxx> wrote:
>
> If mmc_sdio_init_uhs_card() fails, e.g. because tuning finds no
> working sample phase, card initialisation fails and the card is not
> usable at all, even though it would work fine in high-speed mode.
>
> This happens for example on the FriendlyElec NanoPi R2S Plus when the
> SDIO pins of the RTL8822CS Wi-Fi module are left at their default 4 mA
> drive strength:
>
>   dwmmc_rockchip ff5f0000.mmc: All phases bad!
>   mmc2: tuning execution failed: -5
>   mmc2: error -5 whilst initialising SDIO card
>   [... repeated for every init frequency ...]
>   mmc2: Failed to initialize a non-removable card
>
> There is already a fallback for a failure to read the CCCR in UHS mode:
> reset the card and restart the init sequence without R4_18V_PRESENT.
> Do the same when UHS init fails, so that the card comes up in
> high-speed mode instead:
>
>   mmc2: UHS init failed (-5), retrying without UHS
>   mmc2: Skipping voltage switch
>   mmc2: new high speed SDIO card at address 0001
>
> The fallback is taken at most once, as the retry doesn't request UHS.
>
> Reviewed-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
> Signed-off-by: Deomid rojer Ryabkov <rojer@xxxxxxxx>
> ---
>  drivers/mmc/core/sdio.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/sdio.c b/drivers/mmc/core/sdio.c
> index 83085e76486..6787fdf1c53 100644
> --- a/drivers/mmc/core/sdio.c
> +++ b/drivers/mmc/core/sdio.c
> @@ -867,8 +867,14 @@ static int mmc_sdio_init_card(struct mmc_host *host, u32 ocr,
>         /* Only if card supports 1.8v and UHS signaling */
>         if ((ocr & R4_18V_PRESENT) && card->sw_caps.sd3_bus_mode) {
>                 err = mmc_sdio_init_uhs_card(card);
> -               if (err)
> -                       goto remove;
> +               if (err) {
> +                       pr_warn("%s: UHS init failed (%d), retrying without UHS\n",
> +                               mmc_hostname(host), err);
> +                       mmc_sdio_pre_init(host, ocr_card,
> +                                         card != oldcard ? card : NULL);

Is this really correct?

If there is an oldcard we should *not* pass the card (since it would
be equal to oldcard) to mmc_sdio_pre_init() as it would remove it.

If there is no oldcard (oldcard == NULL), we should pass the card to
mmc_sdio_pre_init() to make it remove it.

In other words, how about just:
"oldcard ? NULL : card"

> +                       retries = 0;
> +                       goto try_again;
> +               }
>         } else {
>                 /*
>                  * Switch to high-speed (if supported).
> --
> 2.53.0
>

Kind regards
Uffe