hw/ide/ahci: fix legacy software reset

hw/ide/ahci: fix legacy software reset

Legacy software contains a standard mechanism for generating a reset to a
Serial ATA device - setting the SRST (software reset) bit in the Device
Control register.

Serial ATA has a more robust mechanism called COMRESET, also referred to
as port reset. A port reset is the preferred mechanism for error
recovery and should be used in place of software reset.

Commit e2a5d9b3d9c3 ("hw/ide/ahci: simplify and document PxCI handling")
improved the handling of PxCI, such that PxCI gets cleared after handling
a non-NCQ, or NCQ command (instead of incorrectly clearing PxCI after
receiving anything - even a FIS that failed to parse, which should NOT
clear PxCI, so that you can see which command slot that caused an error).

However, simply clearing PxCI after a non-NCQ, or NCQ command, is not
enough, we also need to clear PxCI when receiving a SRST in the Device
Control register.

A legacy software reset is performed by the host sending two H2D FISes,
the first H2D FIS asserts SRST, and the second H2D FIS deasserts SRST.

The first H2D FIS will not get a D2H reply, and requires the FIS to have
the C bit set to one, such that the HBA itself will clear the bit in PxCI.

The second H2D FIS will get a D2H reply once the diagnostic is completed.
The clearing of the bit in PxCI for this command should ideally be done
in ahci_init_d2h() (if it was a legacy software reset that caused the
reset (a COMRESET does not use a command slot)). However, since the reset
value for PxCI is 0, modify ahci_reset_port() to actually clear PxCI to 0,
that way we can avoid complex logic in ahci_init_d2h().

This fixes an issue for FreeBSD where the device would fail to reset.
The problem was not noticed in Linux, because Linux uses a COMRESET
instead of a legacy software reset by default.

Fixes: e2a5d9b3d9c3 ("hw/ide/ahci: simplify and document PxCI handling")
Reported-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Message-ID: <20231108222657.117984-1-nks@flawful.org>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>