ata: libahci: re-enable FBS after error handling on a port multiplier

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>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20261012103917.389-1-illofspeed@gmail.com
Signed-off-by: Niklas Cassel <cassel@kernel.org>

0 files changed, 0 insertions, 0 deletions