Re: [PATCH] scsi: ufs: add a quirk to disable FUA support

[Eric Biggers <ebiggers@kernel.org>]

On Tue, May 31, 2022 at 01:10:53PM -0700, Jaegeuk Kim wrote:
> UFS stack shows very low performance of FUA comparing to write and cache_flush.
> Let's add a quirk to adjust it.
> 
> E.g., average latency according to the chunk size of write
> 
> Write(us/KB)	4	64	256	1024	2048
> FUA		873.792	754.604	995.624	1011.67	1067.99
> CACHE_FLUSH	824.703	712.98	800.307	1019.5	1037.37
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>  drivers/scsi/ufs/ufshcd.c | 3 +++
>  drivers/scsi/ufs/ufshcd.h | 5 +++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 3f9caafa91bf..811f3467879c 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -5035,6 +5035,9 @@ static int ufshcd_slave_configure(struct scsi_device *sdev)
>  	 */
>  	sdev->silence_suspend = 1;
>  
> +	if (hba->quirks & UFSHCD_QUIRK_BROKEN_FUA)
> +		sdev->broken_fua = 1;
> +
>  	ufshcd_crypto_register(hba, q);
>  
>  	return 0;
> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> index 94f545be183a..6c480c6741d6 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -602,6 +602,11 @@ enum ufshcd_quirks {
>  	 * support physical host configuration.
>  	 */
>  	UFSHCD_QUIRK_SKIP_PH_CONFIGURATION		= 1 << 16,
> +
> +	/*
> +	 * This quirk disables FUA support.
> +	 */
> +	UFSHCD_QUIRK_BROKEN_FUA				= 1 << 17,
>  };

"Broken" is ambiguous.  IIUC, the issue is that FUA performance is very bad, not
that it doesn't work.  Can you clarify the intent in the comment?

Also, this patch does nothing by itself.  Which UFS host driver(s) need this
quirk bit?  Can you update them to use it?  Or do they all need this, in which
case a quirk bit would be unnecessary?

- Eric