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

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 05/31, Eric Biggers wrote:
> 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?

My intent is FUA was supposed to be better than write+cache_flush.

> 
> 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?

Likewise other quick bits, using this is up to SoC or UFS vendors. I
think that combination is up to OEMs who is building the product.

> 
> - Eric