Re: [PATCH 6/6] scsi: mvsas: Use sas_task_find_rq() for tagging

[John Garry]

On 29/09/2022 03:22, Damien Le Moal wrote:
> On 9/28/22 21:27, John Garry wrote:
> > The request associated with a scsi command coming from the block layer
> > has a unique tag, so use that when possible for getting a slot.
> >
> > Unfortunately we don't support reserved commands in the SCSI midlayer yet.
> > As such, SMP tasks - as an example - will not have a request associated, so
> > in the interim continue to manage those tags for that type of sas_task
> > internally.
> >
> > We reserve an arbitrary 4 tags for these internal tags. Indeed, we already
> > decrement MVS_RSVD_SLOTS by 2 for the shost can_queue when flag
> > MVF_FLAG_SOC is set. This change was made in commit 20b09c2992fef
> > ("[PATCH] [SCSI] mvsas: add support for 94xx; layout change; bug fixes"),
> > but what those 2 slots are used for is not obvious.
> >
> > Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
> > ---
> >   drivers/scsi/mvsas/mv_defs.h |  1 +
> >   drivers/scsi/mvsas/mv_init.c |  4 ++--
> >   drivers/scsi/mvsas/mv_sas.c  | 22 +++++++++++++++++-----
> >   drivers/scsi/mvsas/mv_sas.h  |  1 -
> >   4 files changed, 20 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/scsi/mvsas/mv_defs.h b/drivers/scsi/mvsas/mv_defs.h
> > index 7123a2efbf58..8ef174cd4d37 100644
> > --- a/drivers/scsi/mvsas/mv_defs.h
> > +++ b/drivers/scsi/mvsas/mv_defs.h
> > @@ -40,6 +40,7 @@ enum driver_configuration {
> >   	MVS_ATA_CMD_SZ		= 96,	/* SATA command table buffer size */
> >   	MVS_OAF_SZ		= 64,	/* Open address frame buffer size */
> >   	MVS_QUEUE_SIZE		= 64,	/* Support Queue depth */
> > +	MVS_RSVD_SLOTS		= 4,
> >   	MVS_SOC_CAN_QUEUE	= MVS_SOC_SLOTS - 2,
> >   };
> >   
> > diff --git a/drivers/scsi/mvsas/mv_init.c b/drivers/scsi/mvsas/mv_init.c
> > index c85fb812ad43..d834ed9e8e4a 100644
> > --- a/drivers/scsi/mvsas/mv_init.c
> > +++ b/drivers/scsi/mvsas/mv_init.c
> > @@ -284,7 +284,7 @@ static int mvs_alloc(struct mvs_info *mvi, struct Scsi_Host *shost)
> >   			printk(KERN_DEBUG "failed to create dma pool %s.\n", pool_name);
> >   			goto err_out;
> >   	}
> > -	mvi->tags_num = slot_nr;
> > +	mvi->tags_num = MVS_RSVD_SLOTS;
>
> Same comment as for pm8001: do you really need this field if the value
> is always MVS_RSVD_SLOTS ?

Right, I don't need this struct member. Again I can just use this macro 
directly.

> >   
> >   	return 0;
> >   err_out:
> > @@ -367,7 +367,7 @@ static struct mvs_info *mvs_pci_alloc(struct pci_dev *pdev,
> >   	mvi->sas = sha;
> >   	mvi->shost = shost;
> >   
> > -	mvi->tags = kzalloc(MVS_CHIP_SLOT_SZ>>3, GFP_KERNEL);
> > +	mvi->tags = kzalloc(MVS_RSVD_SLOTS, GFP_KERNEL);
>
> Field name ? reserved_tags ?
> Also, the alloc seems wrong. This will allocate 4 bytes, but you only
> need 4 bits. You could make this an unsigned long and not allocate
> anything. 

Well spotted. I should have questioned more why they had >>3 previously.

But I would rather keep as a bitmap, i.e. *unsigned long for simplicity.

> Same remark for pm8001 by the way.

I think it's ok as it uses bitmap_zalloc()

> That would cap MVS_RSVD_SLOTS to BITS_PER_LONG maximum, but that is easy
> to check at compile time with a #if/#error.

As above, I'd rather keep as a bitmap. It's a little inefficient, but is 
a one off in the driver.

Thanks,
John