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

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

On 31/05/22 23:10, 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

Wouldn't it depend on how much data might be in the cache?
Do you have real-world use-cases where the difference is measurable?

> 
> 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,

Wouldn't it be more appropriate to make it a UFS_DEVICE_QUIRK_
since it presumably depends on the UFS device not the host controller?

Also, as already commented by others, there needs to be a user of
the quirk

>  };
>  
>  enum ufshcd_caps {