Re: [PATCH] mmc: sdhci-msm: Add retries when all tuning phases are found valid

[Ulf Hansson]

On Thu, 27 Aug 2020 at 16:59, Douglas Anderson <dianders@xxxxxxxxxxxx> wrote:
>
> As the comments in this patch say, if we tune and find all phases are
> valid it's _almost_ as bad as no phases being found valid.  Probably
> all phases are not really reliable but we didn't detect where the
> unreliable place is.  That means we'll essentially be guessing and
> hoping we get a good phase.
>
> This is not just a problem in theory.  It was causing real problems on
> a real board.  On that board, most often phase 10 is found as the only
> invalid phase, though sometimes 10 and 11 are invalid and sometimes
> just 11.  Some percentage of the time, however, all phases are found
> to be valid.  When this happens, the current logic will decide to use
> phase 11.  Since phase 11 is sometimes found to be invalid, this is a
> bad choice.  Sure enough, when phase 11 is picked we often get mmc
> errors later in boot.
>
> I have seen cases where all phases were found to be valid 3 times in a
> row, so increase the retry count to 10 just to be extra sure.
>
> Fixes: 415b5a75da43 ("mmc: sdhci-msm: Add platform_execute_tuning implementation")
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

Applied for fixes and by adding a stable tag, thanks!

Kind regards
Uffe


> ---
>
>  drivers/mmc/host/sdhci-msm.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
> index b7e47107a31a..1b78106681e0 100644
> --- a/drivers/mmc/host/sdhci-msm.c
> +++ b/drivers/mmc/host/sdhci-msm.c
> @@ -1165,7 +1165,7 @@ static void sdhci_msm_set_cdr(struct sdhci_host *host, bool enable)
>  static int sdhci_msm_execute_tuning(struct mmc_host *mmc, u32 opcode)
>  {
>         struct sdhci_host *host = mmc_priv(mmc);
> -       int tuning_seq_cnt = 3;
> +       int tuning_seq_cnt = 10;
>         u8 phase, tuned_phases[16], tuned_phase_cnt = 0;
>         int rc;
>         struct mmc_ios ios = host->mmc->ios;
> @@ -1221,6 +1221,22 @@ static int sdhci_msm_execute_tuning(struct mmc_host *mmc, u32 opcode)
>         } while (++phase < ARRAY_SIZE(tuned_phases));
>
>         if (tuned_phase_cnt) {
> +               if (tuned_phase_cnt == ARRAY_SIZE(tuned_phases)) {
> +                       /*
> +                        * All phases valid is _almost_ as bad as no phases
> +                        * valid.  Probably all phases are not really reliable
> +                        * but we didn't detect where the unreliable place is.
> +                        * That means we'll essentially be guessing and hoping
> +                        * we get a good phase.  Better to try a few times.
> +                        */
> +                       dev_dbg(mmc_dev(mmc), "%s: All phases valid; try again\n",
> +                               mmc_hostname(mmc));
> +                       if (--tuning_seq_cnt) {
> +                               tuned_phase_cnt = 0;
> +                               goto retry;
> +                       }
> +               }
> +
>                 rc = msm_find_most_appropriate_phase(host, tuned_phases,
>                                                      tuned_phase_cnt);
>                 if (rc < 0)
> --
> 2.28.0.297.g1956fa8f8d-goog
>