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

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

On Wed, Mar 18, 2026 at 04:29:51PM +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.

>  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
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