On 06/22/2015 10:43 AM, John Snow wrote: > > > On 06/22/2015 10:38 AM, Stefan Hajnoczi wrote: >> On Fri, Jun 19, 2015 at 09:50:39PM -0400, John Snow wrote: >>> The legacy ide command execution layer will clear any errors >>> outstanding before execution, but the NCQ layer doesn't. Even on >>> success, this register will remain clogged. >>> >>> Clear it out before each NCQ command so the guest can tell if >>> the error code produced after completion is meaningful or not. >>> >>> Signed-off-by: John Snow <js...@redhat.com> --- hw/ide/ahci.c | 2 >>> ++ 1 file changed, 2 insertions(+) >>> >>> diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c index 6bded67..e63ba9b >>> 100644 --- a/hw/ide/ahci.c +++ b/hw/ide/ahci.c @@ -1048,6 +1048,8 >>> @@ static void process_ncq_command(AHCIState *s, int port, >>> uint8_t *cmd_fis, ncq_tfs->lba, ncq_tfs->lba + >>> ncq_tfs->sector_count - 1, ide_state->nb_sectors - 1); >>> >>> + ide_state->error = 0; >> >> I'm not sure it makes sense use ide_state at all in NCQ. >> >> ide_state is per-port and NCQ can issue multiple asynchronous >> commands per port. If process_ncq_command() modifies ide_state, it >> may do that while other commands are still pending or about to be >> processed. >> >> This will clobber ide_state->error. >> > > Good point. The real problem that we need to fix then is in the core > IDE layer, which tends to set a "default error" and waits for > ide_exec_cmd to clear it before execution. > > If we don't clear that bit somehow, we will get failed commands. > > I'll have to do a little research to see if it's safe to remove our > startup error, since it might be part of an ATA signature handshake. >
It is indeed part of a startup signature and should not be removed. > Hmm. > > Maybe it's not actually a problem because any real OS should probably > have issued ATA IDENTIFY (which will clear ERR) by the time they get > to NCQ, so maybe we can scrap this, and I'll adjust the test accordingly > to issue at least IDENTIFY before attempting NCQ. It's not exquisitely clear what the NCQ state machine for SATA should look like -- I need to figure out what a real device might do if you attempt to send it an NCQ command before a "hello." Or I'll just ignore this whole train of thought under the premise that every OS alive will always send an IDENTIFY packet first, and be on my way.
