Re: [PATCH v4 8/8] ata: libata-scsi: Make ata_scsi_qc_complete() more readable

[Igor Pylypiv <ipylypiv@google.com>]

On Mon, Jul 01, 2024 at 11:15:54PM +0200, Niklas Cassel wrote:
> On Mon, Jul 01, 2024 at 07:57:58PM +0000, Igor Pylypiv wrote:
> > The ATA PASS-THROUGH handling logic in ata_scsi_qc_complete() is hard
> > to read/understand. Improve the readability of the code by moving checks
> > into self-explanatory boolean variables.
> > 
> > Additionally, always set SAM_STAT_CHECK_CONDITION when CK_COND=1 because
> > SAT specification mandates that SATL shall return CHECK CONDITION if
> > the CK_COND bit is set.
> > 
> > Co-developed-by: Niklas Cassel <cassel@kernel.org>
> > Signed-off-by: Niklas Cassel <cassel@kernel.org>
> > Signed-off-by: Igor Pylypiv <ipylypiv@google.com>
> > ---
> >  drivers/ata/libata-scsi.c | 21 +++++++++++----------
> >  1 file changed, 11 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> > index a66c177b6087..8f21b3b0bc75 100644
> > --- a/drivers/ata/libata-scsi.c
> > +++ b/drivers/ata/libata-scsi.c
> > @@ -1659,26 +1659,27 @@ static void ata_scsi_qc_complete(struct ata_queued_cmd *qc)
> >  {
> >  	struct scsi_cmnd *cmd = qc->scsicmd;
> >  	u8 *cdb = cmd->cmnd;
> > -	int need_sense = (qc->err_mask != 0) &&
> > -		!(qc->flags & ATA_QCFLAG_SENSE_VALID);
> > -	int need_passthru_sense = (qc->err_mask != 0) ||
> > -		(qc->flags & ATA_QCFLAG_SENSE_VALID);
> > +	bool have_sense = qc->flags & ATA_QCFLAG_SENSE_VALID;
> > +	bool is_ata_passthru = cdb[0] == ATA_16 || cdb[0] == ATA_12;
> > +	bool is_ck_cond_request = cdb[2] & 0x20;
> > +	bool is_error = qc->err_mask != 0;
> >  
> >  	/* For ATA pass thru (SAT) commands, generate a sense block if
> >  	 * user mandated it or if there's an error.  Note that if we
> > -	 * generate because the user forced us to [CK_COND =1], a check
> > +	 * generate because the user forced us to [CK_COND=1], a check
> >  	 * condition is generated and the ATA register values are returned
> >  	 * whether the command completed successfully or not. If there
> > -	 * was no error, we use the following sense data:
> > +	 * was no error, and CK_COND=1, we use the following sense data:
> >  	 * sk = RECOVERED ERROR
> >  	 * asc,ascq = ATA PASS-THROUGH INFORMATION AVAILABLE
> >  	 */
> > -	if (((cdb[0] == ATA_16) || (cdb[0] == ATA_12)) &&
> > -	    ((cdb[2] & 0x20) || need_passthru_sense)) {
> > -		if (!(qc->flags & ATA_QCFLAG_SENSE_VALID))
> > +	if (is_ata_passthru && (is_ck_cond_request || is_error || have_sense)) {
> > +		if (!have_sense)
> >  			ata_gen_passthru_sense(qc);
> >  		ata_scsi_set_passthru_sense_fields(qc);
> > -	} else if (need_sense) {
> > +		if (is_ck_cond_request)
> > +			set_status_byte(qc->scsicmd, SAM_STAT_CHECK_CONDITION);
> > +	} else if (is_error && !have_sense) {
> >  		ata_gen_ata_sense(qc);
> >  	} else {
> >  		/* Keep the SCSI ML and status byte, clear host byte. */
> > -- 
> > 2.45.2.803.g4e1b14247a-goog
> > 
> 
> Reviewed-by: Niklas Cassel <cassel@kernel.org>
> 
> However: I really think that this patch should be squashed with patch 2/8.
> 
> Sure, the changes in this patch will make it harder to backport...
> but, even patch 2/8 will be a pain to backport...
> 
> And this patch will need to have CC: stable and be backported as well...
> (such that we always set CHECK_CONDITION when CK_COND=1), so I strongly
> suggest that we should squash these, since it will probably be way simpler
> to backport the patch that is "patch 2/8 squashed with this patch",
> compared to backporting patch 2/8, and then backporting this patch.
> (That would just give two patches that will need manual backport, rather
> than one patch that needs manual backport.)
> 
> Both of these are fixing incorrect sense data for ATA passthough commands
> anyway.

Agreed, it makes more sense to squash. Squashed the patches in v5.

I really appreciate your thorough reviews and feedback, Niklas! Thank you!

Best,
Igor
> 
> 
> Kind regards,
> Niklas