Re: [PATCH v4] ata: libahci: re-enable FBS after error handling on a port multiplier

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

On 2026/10/12 12:39, Kyrylo Biryuk wrote:
> ahci_do_softreset() disables FBS before resetting a device behind a port
> multiplier, as required by AHCI 1.2 section 9.3.9, and re-enables it only
> when that softreset succeeds. If it fails, for example because a
> hot-plugged drive is still spinning up ("softreset failed (device not
> ready)"), EH escalates to a hardreset of the PMP link, and nothing turns
> FBS back on: only ahci_pmp_attach() does, which runs at the next boot.
> The port keeps working with command-based switching until then.
> 
> Seen on a Marvell 88SE9235 (1b4b:9235) with Marvell 88SM9705 port
> multipliers (1b4b:9705, in a Synology DX1222 expansion unit): after
> hot-plugging a drive, the kernel logged "FBS is disabled" followed by
> "softreset failed (device not ready)" and a PMP hardreset, and never
> "FBS is enabled" again (twice, on two different ports).
> 
> At the end of ahci_error_handler(), re-enable FBS if a PMP is still
> attached and FBS is supported but disabled.
> 
> Fixes: 89dafa20f3da ("ahci: disabled FBS prior to issuing software reset")
> Assisted-by: LLM
> Signed-off-by: Kyrylo Biryuk <illofspeed@gmail.com>

Looks good.

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

-- 
Damien Le Moal
Western Digital Research