Re: [PATCH v3] hw/ide/ahci: fix legacy software reset

[Kevin Wolf <kwolf@redhat.com>]

Am 08.11.2023 um 23:26 hat Niklas Cassel geschrieben:
> From: Niklas Cassel <niklas.cassel@wdc.com>
> 
> 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>

Thanks, applied to the block branch.

Kevin