Re: [PATCH v3 0/2] ata: fix deferred QC handling for port multipliers

[Niklas Cassel <cassel@kernel.org>]

On Tue, May 12, 2026 at 10:58:04AM +0900, Damien Le Moal wrote:
> On 5/9/26 04:50, Niklas Cassel wrote:
> > Hello all,
> > 
> > Tommy Kelly reported a regression with PMP that use CBS:
> > https://lore.kernel.org/linux-ide/ce09cc21-a8e9-4845-b205-35411e22fba9@tkel.ly/
> > 
> > It turns out that the ap->excl_link logic used for PMP that use CBS is
> > incompatible with the deferred qc issuing via a workqueue.
> > This is fixed in patch 1/2.
> > 
> > While looking at the code, it turns out that the deferred qc issuing via
> > workqueue is misdesigned. It assumed that we can't mix NCQ and non-NCQ
> > commands on the same port. The limitation is that you can not mix NCQ and
> > non-NCQ commands on the same drive. However, with a PMP with FBS, you can
> > issue (mixed NCQ and non-NCQ commands) to the different drives. Thus, move
> > the saved deferred QC from struct ata_port to struct ata_link. This is
> > fixed in patch 2/2.
> > 
> > 
> 
> What are the changes from v2 ?

There are the changes since v2, I simply forgot to change v1 to v2.


> 
> > Changes since v1:
> > -Avoid a local variable in sata_pmp_qc_defer_cmd_switch(), call
> >  ata_std_qc_defer(qc) inside the switch() directly instead.
> > -Fix a typo, such that the the code actually compiles... Sorry for that.
> > 
> > 
> > Niklas Cassel (2):
> >   ata: libata-scsi: do not use the deferred QC feature on PMPs with CBS
> >   ata: libata-scsi: do not needlessly defer commands when using PMP with
> >     FBS
> > 
> >  drivers/ata/libata-core.c | 16 ++++---
> >  drivers/ata/libata-eh.c   |  8 ++--
> >  drivers/ata/libata-pmp.c  | 26 +++++++++--
> >  drivers/ata/libata-scsi.c | 95 ++++++++++++++++++++++++---------------
> >  include/linux/libata.h    |  8 ++--
> >  5 files changed, 101 insertions(+), 52 deletions(-)
> > 
> 
> 
> -- 
> Damien Le Moal
> Western Digital Research