Re: [PATCH v5 4/4] ata: libata-scsi: do not needlessly defer commands when using PMP with FBS

[Damien Le Moal <dlemoal@kernel.org>]

On 2026/05/14 9:39, Niklas Cassel wrote:
> The SATA specification does not allow a non-NCQ command to be issued while

s/SATA/ATA (or ACS)

> an NCQ command is outstanding.
> 
> Commit 0ea84089dbf6 ("ata: libata-scsi: avoid Non-NCQ command starvation")
> introduced a feature where a deferred non-NCQ command gets issued from a
> workqueue. The design stores a single non-NCQ command per port.
> 
> However, when using Port Multipliers (PMPs), specifically PMPs that
> support FIS-Based Switching (FBS), non-NCQ and NCQ commands can be mixed
> on the same port, just not for the same link, see e.g. ata_std_qc_defer()
> which is, and always has operated on a per-link basis.
> 
> Therefore, move the deferred_qc from struct ata_port to struct ata_link.
> This way, when using a PMP with FBS, we will not needlessly defer commands
> to all other links, just because one link issued a non-NCQ command while
> having an NCQ command outstanding. Only commands for that specific link
> will be deferred.
> 
> Fixes: 0ea84089dbf6 ("ata: libata-scsi: avoid Non-NCQ command starvation")
> Signed-off-by: Niklas Cassel <cassel@kernel.org>

Looks good.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research