Hi Akinobu,
On Fri, May 8, 2015 at 10:33 PM, Akinobu Mita <akinobu.mita@xxxxxxxxx> wrote:
>
> Hi Kyuho,
>
> 2015-05-07 22:06 GMT+09:00 Kyuho Choi <chlrbgh0@xxxxxxxxx>:
> > This patch disables write_same for ufs.
> >
> > Signed-off-by: Kyuho Choi <kyuho.choi@xxxxxx>
> > ---
> > drivers/scsi/ufs/ufshcd.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > index 648a446..6f770cd 100644
> > --- a/drivers/scsi/ufs/ufshcd.c
> > +++ b/drivers/scsi/ufs/ufshcd.c
> > @@ -4255,6 +4255,7 @@ static struct scsi_host_template ufshcd_driver_template = {
> > .max_host_blocked = 1,
> > .use_blk_tags = 1,
> > .track_queue_depth = 1,
> > + .no_write_same = 1,
> > };
>
> Is there any specific reason to disable WRITE_SAME in the host
> controller level?
Nope.
But, according to UFS specification, does not support WRITE_SAME until UFS 2.0.
So I thought host controller does not need WRITE_SAME command for UFS device.
>
> no_write_same flag in scsi_host_template was introduced by commit
> 54b2b50c ("[SCSI] Disable WRITE SAME for RAID and virtual host adapter
> drivers") for RAID and virtual host adapter drivers which can lead
> to adapter firmware hangs or excessive I/O errors.
Right. I'd refer that for this patch.
>
> The UFS device that does not support WRITE SAME should return
> ILLEGAL_REQUEST sense key (and with INVALID COMMAND OPCODE code for
> example). If there is a specific product model/revision which causes
> an undesirable result by WRITE_SAME, we should disable only when
> such device is detected. Otherwise I think this patch could conflict
> with any attempts to support WRITE SAME by some vendors who want it in
> their products or future UFS specification change.
Right. UFS device always should return ILLEGAL_REQUEST about WRITE_SAME command.
But I didn't consider of specification change in future.
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