[PATCH] use mmiowb in qla1280.c

[PATCH] use mmiowb in qla1280.c

[Jesse Barnes]

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There are a few spots in qla1280.c that don't need a full PCI write flush to 
the device, but rather a simple write ordering guarantee.  This patch changes 
some of the PIO reads that cause write flushes into mmiowb calls instead, 
which is a lighter weight way of ensuring ordering.

Jes and James, can you ack this and/or push it in via the SCSI BK tree?

Thanks,
Jesse

Signed-off-by: Jeremy Higdon <jeremy@sgi.com>
Signed-off-by: Jesse Barnes <jbarnes@sgi.com>



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===== drivers/scsi/qla1280.c 1.69 vs edited =====
--- 1.69/drivers/scsi/qla1280.c	2004-10-20 06:46:21 -07:00
+++ edited/drivers/scsi/qla1280.c	2004-10-21 16:06:11 -07:00
@@ -3400,7 +3400,8 @@
 	sp->flags |= SRB_SENT;
 	ha->actthreads++;
 	WRT_REG_WORD(&reg->mailbox4, ha->req_ring_index);
-	(void) RD_REG_WORD(&reg->mailbox4); /* PCI posted write flush */
+	/* Enforce mmio write ordering; see comment in qla1280_isp_cmd(). */
+	mmiowb();
 
  out:
 	if (status)
@@ -3668,7 +3669,8 @@
 	sp->flags |= SRB_SENT;
 	ha->actthreads++;
 	WRT_REG_WORD(&reg->mailbox4, ha->req_ring_index);
-	(void) RD_REG_WORD(&reg->mailbox4); /* PCI posted write flush */
+	/* Enforce mmio write ordering; see comment in qla1280_isp_cmd(). */
+	mmiowb();
 
 out:
 	if (status)
@@ -3778,9 +3780,21 @@
 	} else
 		ha->request_ring_ptr++;
 
-	/* Set chip new ring index. */
+	/*
+	 * Update request index to mailbox4 (Request Queue In).
+	 * The mmiowb() ensures that this write is ordered with writes by other
+	 * CPUs.  Without the mmiowb(), it is possible for the following:
+	 *    CPUA posts write of index 5 to mailbox4
+	 *    CPUA releases host lock
+	 *    CPUB acquires host lock
+	 *    CPUB posts write of index 6 to mailbox4
+	 *    On PCI bus, order reverses and write of 6 posts, then index 5,
+	 *       causing chip to issue full queue of stale commands
+	 * The mmiowb() prevents future writes from crossing the barrier.
+	 * See Documentation/DocBook/deviceiobook.tmpl for more information.
+	 */
 	WRT_REG_WORD(&reg->mailbox4, ha->req_ring_index);
-	(void) RD_REG_WORD(&reg->mailbox4); /* PCI posted write flush */
+	mmiowb();
 
 	LEAVE("qla1280_isp_cmd");
 }

Re: [PATCH] use mmiowb in qla1280.c

[Jes Sorensen]

>>>>> "Jesse" == Jesse Barnes <jbarnes@engr.sgi.com> writes:

Jesse> There are a few spots in qla1280.c that don't need a full PCI
Jesse> write flush to the device, but rather a simple write ordering
Jesse> guarantee.  This patch changes some of the PIO reads that cause
Jesse> write flushes into mmiowb calls instead, which is a lighter
Jesse> weight way of ensuring ordering.

Jesse> Jes and James, can you ack this and/or push it in via the SCSI
Jesse> BK tree?

ACK!

James will you push this one?

Cheers,
Jes

Re: [PATCH] use mmiowb in qla1280.c

[James Bottomley]

On Thu, 2004-10-21 at 19:17, Jesse Barnes wrote:
> There are a few spots in qla1280.c that don't need a full PCI write flush to 
> the device, but rather a simple write ordering guarantee.  This patch changes 
> some of the PIO reads that cause write flushes into mmiowb calls instead, 
> which is a lighter weight way of ensuring ordering.
> 
> Jes and James, can you ack this and/or push it in via the SCSI BK tree?

This doesn't seem to work:

  CC [M]  drivers/scsi/qla1280.o
drivers/scsi/qla1280.c: In function `qla1280_64bit_start_scsi':
drivers/scsi/qla1280.c:3404: warning: implicit declaration of function
`mmiowb'

  MODPOST
*** Warning: "mmiowb" [drivers/scsi/qla1280.ko] undefined!

James

Re: [PATCH] use mmiowb in qla1280.c

[Jesse Barnes]

On Sunday, October 24, 2004 9:20 am, James Bottomley wrote:
> On Thu, 2004-10-21 at 19:17, Jesse Barnes wrote:
> > There are a few spots in qla1280.c that don't need a full PCI write flush
> > to the device, but rather a simple write ordering guarantee.  This patch
> > changes some of the PIO reads that cause write flushes into mmiowb calls
> > instead, which is a lighter weight way of ensuring ordering.
> >
> > Jes and James, can you ack this and/or push it in via the SCSI BK tree?
>
> This doesn't seem to work:
>
>   CC [M]  drivers/scsi/qla1280.o
> drivers/scsi/qla1280.c: In function `qla1280_64bit_start_scsi':
> drivers/scsi/qla1280.c:3404: warning: implicit declaration of function
> `mmiowb'
>
>   MODPOST
> *** Warning: "mmiowb" [drivers/scsi/qla1280.ko] undefined!

Only works in Andrew's tree until he pushes mmiowb to Linus.

Jesse

Re: [PATCH] use mmiowb in qla1280.c

[Andrew Morton]

Jesse Barnes <jbarnes@engr.sgi.com> wrote:
>
> > *** Warning: "mmiowb" [drivers/scsi/qla1280.ko] undefined!
> 
>  Only works in Andrew's tree until he pushes mmiowb to Linus.

I haven't been following this stuff at all closely and I need help
determining which patches should be pushed, and when.  Please.

Re: [PATCH] use mmiowb in qla1280.c

[Jesse Barnes]

On Monday, October 25, 2004 12:02 pm, Andrew Morton wrote:
> Jesse Barnes <jbarnes@engr.sgi.com> wrote:
> > > *** Warning: "mmiowb" [drivers/scsi/qla1280.ko] undefined!
> >
> >  Only works in Andrew's tree until he pushes mmiowb to Linus.
>
> I haven't been following this stuff at all closely and I need help
> determining which patches should be pushed, and when.  Please.

I think it's safe to push the main mmiowb() patch now, then James and the 
netdev tree can start including driver changes to make use of it.

Thanks,
Jesse