Re: [PATCH] mmc: rpmb: do not force a retune before RPMB switch

[Adrian Hunter <adrian.hunter@intel.com>]

On 4/12/23 17:01, Jorge Ramirez-Ortiz wrote:
> Requesting a retune before switching to the RPMB partition has been
> observed to cause CRC errors on the RPMB reads (-EILSEQ).

There are still 2 concerns:
1) We don't really know the root cause.  Have you determined
if here are CRC errors in the main partition also?
2) Forcing this on everyone

The original idea was that because re-tuning cannot be
done in RPMB, the need to re-rune in RPMB could be avoided
by always re-tuning before switching to RPMB and then switching
straight back. IIRC re-tuning should guarantee at least 4MB
more I/O without issue.

The alternative to dropping re-tuning in this case could
be to add a retry loop for MMC_DRV_OP_IOCTL_RPMB if the error
is -EILSEQ


> 
> Since RPMB reads can not be retried, the clients would be directly
> affected by the errors.
> 
> This commit disables the request prior to RPMB switching while allowing
> the pause interface to still request a retune before the pause for other
> use cases.
> 
> This was verified with the sdhci-of-arasan driver (ZynqMP) configured
> for HS200 using two separate eMMC cards (DG4064 and 064GB2). In both
> cases, the error was easy to reproduce triggering every few tenths of
> reads.
> 
> Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> ---
>  drivers/mmc/core/block.c | 2 +-
>  drivers/mmc/core/host.c  | 7 ++++---
>  drivers/mmc/core/host.h  | 2 +-
>  3 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index f9a5cffa64b1..1d69078ad9b2 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -859,7 +859,7 @@ static int mmc_blk_part_switch_pre(struct mmc_card *card,
>  			if (ret)
>  				return ret;
>  		}
> -		mmc_retune_pause(card->host);
> +		mmc_retune_pause(card->host, false);
>  	}
>  
>  	return ret;
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index 096093f7be00..a9b95aaa2235 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -119,13 +119,14 @@ void mmc_retune_enable(struct mmc_host *host)
>  
>  /*
>   * Pause re-tuning for a small set of operations.  The pause begins after the
> - * next command and after first doing re-tuning.
> + * next command and, if retune is set, after first doing re-tuning.
>   */
> -void mmc_retune_pause(struct mmc_host *host)
> +void mmc_retune_pause(struct mmc_host *host, bool retune)
>  {
>  	if (!host->retune_paused) {
>  		host->retune_paused = 1;
> -		mmc_retune_needed(host);
> +		if (retune)
> +			mmc_retune_needed(host);

Better to just drop mmc_retune_needed(host);

>  		mmc_retune_hold(host);

There is still a small chance that re-tuning
is needed anyway in which case it will still be done.

>  	}
>  }
> diff --git a/drivers/mmc/core/host.h b/drivers/mmc/core/host.h
> index 48c4952512a5..321776b52270 100644
> --- a/drivers/mmc/core/host.h
> +++ b/drivers/mmc/core/host.h
> @@ -18,7 +18,7 @@ void mmc_retune_disable(struct mmc_host *host);
>  void mmc_retune_hold(struct mmc_host *host);
>  void mmc_retune_release(struct mmc_host *host);
>  int mmc_retune(struct mmc_host *host);
> -void mmc_retune_pause(struct mmc_host *host);
> +void mmc_retune_pause(struct mmc_host *host, bool retune);
>  void mmc_retune_unpause(struct mmc_host *host);
>  
>  static inline void mmc_retune_clear(struct mmc_host *host)