linux-kernel - Re: [RFC PATCH] AHCI: speed up resume

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Message-Id: <1215149537.3068.18.camel@rzhang-dt.sh.intel.com>
Date:	Fri, 04 Jul 2008 13:32:17 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-pm <linux-pm@...ts.linux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [RFC PATCH] AHCI: speed up resume


On Fri, 2008-07-04 at 10:48 +0800, Tejun Heo wrote:
> Hello, Zhang.
> 
> Zhang Rui wrote:
> > During S3 resume, AHCI driver sleeps 1 second to wait for the HBA
> reset
> > to finish. This is luxurious, :)
> >
> > According to the AHCI 1.2 spec, We should poll the HOST_CTL
> register,
> > and return error if the host reset is not finished within 1 second.
> >
> > Test results show that the HBA reset can be done quickly(in usecs).
> > And this patch may save nearly 1 second during resume.
> >
> > Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> > --
> >  drivers/ata/ahci.c |   17 ++++++++++++++---
> >  1 file changed, 14 insertions(+), 3 deletions(-)
> >
> > Index: linux-2.6/drivers/ata/ahci.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/ata/ahci.c 2007-05-03 11:06:33.000000000
> +0800
> > +++ linux-2.6/drivers/ata/ahci.c      2008-07-02 16:25:54.000000000
> +0800
> > @@ -1073,18 +1073,29 @@
> > 
> >       /* global controller reset */
> >       if (!ahci_skip_host_reset) {
> > +             int delay = msecs_to_jiffies(1000);
> > +             int timeout;
> > +
> >               tmp = readl(mmio + HOST_CTL);
> >               if ((tmp & HOST_RESET) == 0) {
> >                       writel(tmp | HOST_RESET, mmio + HOST_CTL);
> >                       readl(mmio + HOST_CTL); /* flush */
> >               }
> > 
> > -             /* reset must complete within 1 second, or
> > +             /*
> > +              * to perform host reset, OS should set HOST_RESET
> > +              * and poll until this bit is read to be "0"
> > +              * reset must complete within 1 second, or
> >                * the hardware should be considered fried.
> >                */
> > -             ssleep(1);
> > +             timeout = jiffies + delay;
> > +             while (jiffies < timeout) {
> > +                     tmp = readl(mmio + HOST_CTL);
> > +                     if (!(tmp & HOST_RESET))
> > +                             break;
> > +                     cpu_relax();
> > +             }
> 
> Looks good in principle.  Just two things...
> 
> 1. Please don't busy-loop.  e.g. No one would notice 10ms delay
> between
> polls.
> 
> 2. Please use ata_wait_register().
> 
Thanks for review, refreshed patch attached. :)

From: Zhang Rui <rui.zhang@...el.com>

During resume, sleep 1 second to wait for the HBA reset
to finish is a waste of time.

According to the AHCI 1.2 spec,
We should poll the HOST_CTL register,
and return error if the host reset is not
finished within 1 second.

Test results show that the HBA reset can be done quickly(in usecs).
And this patch may save nearly 1 second during resume.

Signed-off-by: Zhang Rui <rui.zhang@...el.com>
--
 drivers/ata/ahci.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Index: linux-2.6/drivers/ata/ahci.c
===================================================================
--- linux-2.6.orig/drivers/ata/ahci.c	2008-07-04 09:49:05.000000000 +0800
+++ linux-2.6/drivers/ata/ahci.c	2008-07-04 11:31:30.000000000 +0800
@@ -1079,12 +1079,15 @@
 			readl(mmio + HOST_CTL); /* flush */
 		}
 
-		/* reset must complete within 1 second, or
+		/*
+ 		 * to perform host reset, OS should set HOST_RESET
+		 * and poll until this bit is read to be "0".
+ 		 * reset must complete within 1 second, or
 		 * the hardware should be considered fried.
 		 */
-		ssleep(1);
+		tmp = ata_wait_register(mmio + HOST_CTL, HOST_RESET,
+					HOST_RESET, 10, 1000);
 
-		tmp = readl(mmio + HOST_CTL);
 		if (tmp & HOST_RESET) {
 			dev_printk(KERN_ERR, host->dev,
 				   "controller reset failed (0x%x)\n", tmp);


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