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

[Adrian Hunter]

On 27/08/20 5:58 pm, Douglas Anderson 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>

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

> ---
> 
>  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)
>