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

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

On 6/12/23 09:02, Avri Altman wrote:
>>
>> 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.
> Performance is hardly an issue in the context of RPMB access - 
> For most cases it’s a single frame.

Not sure why you bring up performance.

SDHCI spec says:

"To enable inserting the re-tuning procedure during data transfers,
the data length per read/write command shall be limited up to 4MB."

Which implies re-tuning is needed at most every 4MB, so re-tuning
before RPMB switch and switching straight back, means re-tuning
should never be needed in RPMB.

> 
> Thanks,
> Avri
> 
>>
>> 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)
>