Re: [PATCH] drivers/ide/ide-probe.c, kernel 2.6.23.1

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

Hi,

On Thursday 15 November 2007, Jonas Stare wrote:
> Hi, thanks for the reply. :)
> 
> Bartlomiej Zolnierkiewicz wrote:
> > Hi,
> > 
> > On Monday 12 November 2007, Andrew Morton wrote:
> >> On Fri, 09 Nov 2007 11:22:41 +0100 Jonas Stare <jonas.stare@purplescout.se> wrote:
> >>
> >>> Hi.
> >>>
> >>> This week I ran into a strange hardware problem. During boot I got a 35 
> >>> second delay while waiting for IDE-disks that weren't there to report 
> > 
> > With what chipset and host driver does this happen?
> 
> I am not sure about the chip-set but I think it was vt82c686b. It used 
> the via82cxxx-driver, but only _after_ using the generic ide-code to 
> probe/wait (a long time) for the disks. (This was in Suse 10.1 SP 1.)

AFAIK this means kernel version 2.6.16.xx.

If this is the case maybe the underlying problem has been already fixed
(but it doesn't mean that your patch is not worth applying, quite the
contrary).

> >>> that they were not in a BSY state. The problem was most likely in the 
> >>> hardware but this patch enables you to ignore waiting for disks by 
> >>> setting hdX=noprobe (and not setting the geometry by hand) as a kernel 
> >>> option.
> >>>
> >>> If no noprobe-option is set the code will work (more or less) as the 
> >>> original but if set the code will skip the ide_wait_not_busy() for that 
> >>> drive. Even if there would be a drive there and it is still BSY 
> >>> afterwards it should not matter since it isn't probed for later.
> >>>
> >>> There are other ways to get around the "35-seconds-of-waiting-in-vain", 
> >>> like actually fix the hardware, insert a second drive that works or 
> >>> recompile the kernel with edd-support builtin (atleast I've seen that 
> >>> solution on a forum) and possibly others. But this patch would allow 
> >>> people to get Linux to boot quickly on wonky hardware without having to 
> >>> recompile anything.
> >>> (The code also honors the MAX_DRIVES variable instead of assuming that 
> >>> ther will be 2 drives on the bus.)
> >> I keep on hearing about problems with boot-time IDE probing.  It's public
> >> enemy #1 with the embedded guys.
> > 
> > The problem is that we are not hearing about them.
> > 
> > Please forward the reports to linux-ide@vger.kernel.org.
> > 
> >> It does seem that operator intervention is needed in some fashion.
> >>
> >>> I will be happy for all the comments I can get. :) But be gentle, this 
> >>> is my first patch...
> > 
> > Jonas, could you also put printk() dumping content of 'stat' in
> > ide-iops.c::ide_wait_not_busy() so we can verify that it is not
> > some problem with ide_wait_not_busy() itself.
> > 
> 
> Sorry. :( I don't have access to the hardware anymore (which is a 
> "home-made" embedded machine). But from what I could get from poking 
> around was that the BSY-bit on the slave (that never has or ever will 
> exists) was set, probably because those who built the thing wanted to 
> save money and/or space on that "billionth of a cent"-resistor that Alan 
> Cox talked about.
> 
> >>>    Best regards
> >>>    Jonas Stare
> >>>
> >>> Signed-off-by: Jonas Stare <jonas.stare@purplescout.se>
> >>> --
> >>> diff -u linux-2.6.23.1-orig/drivers/ide/ide-probe.c 
> >>> linux-2.6.23.1/drivers/ide/ide-probe.c
> >>> --- linux-2.6.23.1-orig/drivers/ide/ide-probe.c 2007-10-12 
> >>> 18:43:44.000000000 +0200
> >>> +++ linux-2.6.23.1/drivers/ide/ide-probe.c      2007-11-09 
> >>> 10:43:16.000000000 +0100
> >>> @@ -643,6 +643,7 @@
> >>>   static int wait_hwif_ready(ide_hwif_t *hwif)
> >>>   {
> >>>          int rc;
> >>> +       int unit;
> >>>
> >>>          printk(KERN_DEBUG "Probing IDE interface %s...\n", hwif->name);
> >>>
> >>> @@ -659,20 +660,24 @@
> >>>                  return rc;
> >>>
> > 
> > Hmm, so the first ide_wait_not_busy() (for the currently
> > selected device) is OK and doesn't stall?
> > 
> 
> It didn't stall for me... But even if it had, probe_hwif() will ignore 
> the entire controller if you set "idex=noprobe".
> 
> (From drivers/ide/ide-probe.c)
> 
> static void probe_hwif(ide_hwif_t *hwif, void (*fixup)(ide_hwif_t *hwif))
> {
>          unsigned int unit;
>          unsigned long flags;
>          unsigned int irqd;
> 
>          if (hwif->noprobe)
>                  return;
> 
> 
> >>>          /* Now make sure both master & slave are ready */
> >>> -       SELECT_DRIVE(&hwif->drives[0]);
> >>> -       hwif->OUTB(8, hwif->io_ports[IDE_CONTROL_OFFSET]);
> >>> -       mdelay(2);
> >>> -       rc = ide_wait_not_busy(hwif, 35000);
> >>> -       if (rc)
> >>> -               return rc;
> >>> -       SELECT_DRIVE(&hwif->drives[1]);
> >>> -       hwif->OUTB(8, hwif->io_ports[IDE_CONTROL_OFFSET]);
> >>> -       mdelay(2);
> >>> -       rc = ide_wait_not_busy(hwif, 35000);
> >>> +       for (unit = 0; unit < MAX_DRIVES; ++unit) {
> >>> +               /* Ignore disks that we will not probe for later. */
> >>> +               if (!hwif->drives[unit].noprobe ||
> >>> +                   hwif->drives[unit].forced_geom) {
> > 
> > It is better to check for ->present
> > (->forced_geom implies that ->present is set).
> > 
> 
> Great comment. :) I'll change that right away...
> 
> >>> +                       SELECT_DRIVE(&hwif->drives[unit]);
> >>> +                       hwif->OUTB(8, hwif->io_ports[IDE_CONTROL_OFFSET]);
> >>> +                       mdelay(2);
> >>> +                       rc = ide_wait_not_busy(hwif, 35000);
> >>> +                       /* Exit function with master selected (let's be 
> >>> sane) */
> >>> +                       SELECT_DRIVE(&hwif->drives[0]);
> > 
> > This changes the previous behavior adding an extra SELECT_DRIVE()
> > before trying the slave drive.
> > 
> 
> Mmmm, yes, I know. But I couldn't come up with a clean and nice way to 
> be sure that the first drive is selected. Maybe I could move it inside 
> the if-statement below?

Then the code will miss re-selecting master drive after waiting for
slave one if there were no problems (rc == 0).

What about adding "if (unit)" statement before SELECT_DRIVE() call?

> >>> +                       if (rc)
> >>> +                               return rc;
> >>> +               } else {
> >>> +                       printk(KERN_DEBUG "Skip ide_wait_not_busy for 
> >>> %s:%d\n",
> >>> +                         hwif->name, unit);
> >>> +               }
> >>> +       }
> >>>
> >>> -       /* Exit function with master reselected (let's be sane) */
> >>> -       SELECT_DRIVE(&hwif->drives[0]);
> >>> -
> >>>          return rc;
> >>>   }
> >> Maybe that's the fix, maybe not - I'll defer to others on that (please).
> >>
> >> Your email client is wordwrapping the text, and replaces tabs with spaces. 
> >> Most of them seem to do this nowadays.  For thunderbird, please see
> >> http://mbligh.org/linuxdocs/Email/Clients/Thunderbird

Please fix the issues + wordwrapping and resubmit.

Thanks,
Bart
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