linux-kernel - RE: [PATCH] libahci: fix turning on LEDs in ahci_start

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Date:	Mon, 14 Oct 2013 16:15:55 +0000
From:	"Dorau, Lukasz" <lukasz.dorau@...el.com>
To:	Tejun Heo <tj@...nel.org>
CC:	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] libahci: fix turning on LEDs in ahci_start_port()

On Monday, October 14, 2013 3:21 PM Tejun Heo <tj@...nel.org> wrote:
> On Mon, Oct 14, 2013 at 02:58:19PM +0200, Lukasz Dorau wrote:
> > If EM Transmit bit is busy during init ata_msleep() is called.
> > It is wrong - msleep() should be used instead of ata_msleep(), because
> > if EM Transmit bit is busy for one port, it will be busy for all other
> > ports too, so using ata_msleep() causes wasting tries for another
> > ports.
> >
> > The most common scenario looks like that now (six ports try to
> > transmit a LED meaasege):
> > - port #0 tries for the 1st time and succeeds
> > - ports #1-5 try for the 1st time and sleeps
> > - port #1 tries for the 2nd time and succeeds
> > - ports #2-5 try for the 2nd time and sleeps
> > - port #2 tries for the 3rd time and succeeds
> > - ports #3-5 try for the 3rd time and sleeps
> > - port #3 tries for the 4th time and succeeds
> > - ports #4-5 try for the 4th time and sleeps
> > - port #4 tries for the 5th time and succeeds
> > - port #5 tries for the 5th time and sleeps At this moment port #5
> > wasted all its five tries and failed to initialize.
> > Because there are only 5 (EM_MAX_RETRY) tries available usually only
> > five ports succeed to initialize. The sixth port and next ones usually will fail.
> >
> > If msleep() is used instead of ata_msleep() the first port succeeds to
> > initialize in the first try and next ones usually succeed to initialize in the second
> try.
> 
> Ah, interesting.
> 
> > Signed-off-by: Lukasz Dorau <lukasz.dorau@...el.com>
> > ---
> >  drivers/ata/libahci.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c index
> > acfd0f7..cf38692 100644
> > --- a/drivers/ata/libahci.c
> > +++ b/drivers/ata/libahci.c
> > @@ -779,7 +779,7 @@ static void ahci_start_port(struct ata_port *ap)
> >  							       emp->led_state,
> >  							       4);
> >  				if (rc == -EBUSY)
> > -					ata_msleep(ap, 1);
> > +					msleep(1);
> 
> This is so unobvious.  Can you please add a comment explaining what's going
> on?
> 

OK, I will send the second version of the patch soon.

Thanks,
Lukasz

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