Re: [PATCH] ide: Set IDENTIFY word 93 to 0 on SATA drives

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Mar 18, 2026 at 04:54:45PM +0000, Daniel P. Berrangé wrote:
> On Wed, Mar 18, 2026 at 04:29:51PM +0000, Pedro Falcato wrote:
> > According to the ATA Command Set specification (and the SATA specification
> > too), SATA drives are supposed to set word 93 (which for PATA holds hardware
> > reset results) to 0. As such, clear it when ncq_queues > 0 (which is only true
> > for SATA drives).
> > 
> > Doing so fixes a quirk in Linux where it thinks the AHCI QEMU drive is PATA
> > over a SATA bridge, and thus limits maximum transfer sizes for individual IOs
> > with a:
> > [    1.632121] ata1.00: applying bridge limits
> > 
> > While at it, bump the device's firmware revision for IDENTIFY. This makes it
> > so Linux can avoid enabling a quirk for fixed QEMU releases.
> > 
> > Link: https://lore.kernel.org/linux-ide/20260303183337.1013474-1-pfalcato@suse.de/
> > Cc: qemu-stable@nongnu.org
> > Suggsted-by: Niklas Cassel <cassel@kernel.org>
> > Signed-off-by: Pedro Falcato <pfalcato@suse.de>
> > ---
> > Note: I understand the version bump is vaguely controversial (particularly
> >  exposing the QEMU version in the string) but I don't have a much better
> >  idea. Logically, bumping it to 11.0 for stable releases doesn't make much
> >  sense.
> 
> Bumping the version string changes guest ABI, so such a change should
> normally be tied to a new machine type version, not unconditionally
> changed.  That would also in turn make it unsuitable for QEMU stable
> release branches which don't take changes which affect machine type
> ABI.
> 
> IMHO Linux should just assume any actively maintained distro that
> cares about this problem will fix their QEMU releases and not try
> to add a version specific workaround.

Having said that, possibly the functional fix itself might need to
be tied to the machine type too, given that it is triggering a
behavioural change in the emulation and guest driver ? If that's
the case, then the version could be changed at the same time.

> 
> >  hw/ide/core.c | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/ide/core.c b/hw/ide/core.c
> > index b45abf067b20..89f62f301e94 100644
> > --- a/hw/ide/core.c
> > +++ b/hw/ide/core.c
> > @@ -211,7 +211,15 @@ static void ide_identify(IDEState *s)
> >          put_le16(p + 87, (1 << 14) | 0);
> >      }
> >      put_le16(p + 88, 0x3f | (1 << 13)); /* udma5 set and supported */
> > -    put_le16(p + 93, 1 | (1 << 14) | 0x2000);
> > +    if (s->ncq_queues) {
> > +        /*
> > +         * This is SATA, which is required by the spec to return 0 for this
> > +         * field.
> > +         */
> > +        put_le16(p + 93, 0);
> > +    } else {
> > +        put_le16(p + 93, 1 | (1 << 14) | 0x2000);
> > +    }
> >      /* *(p + 100) := nb_sectors       -- see ide_identify_size */
> >      /* *(p + 101) := nb_sectors >> 16 -- see ide_identify_size */
> >      /* *(p + 102) := nb_sectors >> 32 -- see ide_identify_size */
> > @@ -2660,7 +2668,7 @@ int ide_init_drive(IDEState *s, IDEDevice *dev, IDEDriveKind kind, Error **errp)
> >      if (dev->version) {
> >          pstrcpy(s->version, sizeof(s->version), dev->version);
> >      } else {
> > -        pstrcpy(s->version, sizeof(s->version), qemu_hw_version());
> > +        pstrcpy(s->version, sizeof(s->version), "11.0");
> >      }
> >  
> >      ide_reset(s);
> > -- 
> > 2.53.0
> > 
> > 
> 
> With regards,
> Daniel
> -- 
> |: https://berrange.com       ~~        https://hachyderm.io/@berrange :|
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> 
> 

With regards,
Daniel
-- 
|: https://berrange.com       ~~        https://hachyderm.io/@berrange :|
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