Re: [RFT] major libata update

[Tejun Heo]

Tejun Heo wrote:
> Andrew Morton wrote:
> > No.  In fact, it doesn't even work with the 2.6.17-rc4-mm1 lineup plus 
> > the
> > latest git-libata-all.  It needs this tweak:
> >
> > --- devel/drivers/scsi/ata_piix.c~2.6.17-rc4-mm1-ich8-fix    
> > 2006-05-16 18:36:12.000000000 -0700
> > +++ devel-akpm/drivers/scsi/ata_piix.c    2006-05-16 
> > 18:36:12.000000000 -0700
> > @@ -542,6 +542,14 @@ static unsigned int piix_sata_probe (str
> >          port = map[base + i];
> >          if (port < 0)
> >              continue;
> > +        if (ap->flags & PIIX_FLAG_AHCI) {
> > +            /* FIXME: Port status of AHCI controllers
> > +             * should be accessed in AHCI memory space.  */
> > +            if (pcs & 1 << port)
> > +                present_mask |= 1 << i;
> > +            else
> > +                pcs &= ~(1 << port);
> > +        }
> >          if (ap->flags & PIIX_FLAG_IGNORE_PCS || pcs & 1 << (4 + port))
> >              present_mask |= 1 << i;
> >          else

The above patch doesn't do anything.  The only effect it has is setting 
present_mask according to enabled bits instead of present bits.  I think 
this patch might have helped with probing before the MAP tables for 
ICH6/7 are fixed.

I've done further testing.

* Symptom

ata_piix tries to probe non-existing slave device resulting in timeouts 
during boot probing.  This problem is aggravated by new probing updates 
as it retries two more times before giving up.

* Test results

PATA never has any problem with device detection via signature.  Only 
SATA is affected and interestingly only ATAPI device.  The following is 
the test result on my machine (ICH7R + PX716SA).

  1. combined mode : MAP [IDE IDE P1 P3]

	P1		P3
	-----------------------------
	PX716-SA	empty		P3 ghosted as ATAPI device
	empty		PX716-SA	okay
	PX716-SA	HDD		okay
	HDD		PX716-SA	okay

  2. SATA-only mode : MAP [P0 P2 P1 P3]

	P0		P2
	-----------------------------
	PX716-SA	empty		P2 ghosted as ATAPI device
	empty		PX716-SA	okay
	PX716-SA	HDD		okay
	HDD		PX716-SA	okay

	P1		P3
	-----------------------------
	Identical to #1.

To sum up, it happens when the master slot is occupied by an ATAPI 
device and the corresponding slave slot is empty.  The slave slot 
reports ATAPI signature (probably duplicated from the master) and passes 
all legacy presence test thus resulting in timeout on IDENTIFY.

In all above cases, the PCS register reported correct presence masks.

* Proposed solution

It seems that the only solution is to make use of the PCS presence bits 
somehow.  It is know that 6300ESB family of controllers have flaky 
presence bits (ata_piix marks them with PIIX_FLAG_IGNORE_PCS), but I 
couldn't find any document/errata for PCS bits for any other 
controllers.  So, we can use PCS for all !PIIX_FLAG_IGNORE_PCS 
controllers or take a conservative approach and make use of it only on 
cases where ghosting problem is reported (ICH7 and 8, I guess.  Can 
anyone test 6?).

Please note that we already use some use of the PCS value when probing 
SATA port.  If its value is zero, we skip the port.  It's done this way 
mainly due to historical reasons - until recently ata_piix didn't have 
MAP tables to map PM/PS/SM/SS to specific ports thus used the PCS values 
in rougher form.

Jeff, what do you think?

--
tejun
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