Re: [Qemu-devel] [PATCH] ahci: properly reset PxCMD on HBA reset

[Jason Baron <jbaron@redhat.com>]

On Fri, Aug 31, 2012 at 12:04:59PM -0700, Alexander Graf wrote:
> On 31.08.2012, at 07:23, Jason Baron wrote:
> 
> > On Fri, Aug 31, 2012 at 12:12:22PM +0200, Kevin Wolf wrote:
> >> Am 23.08.2012 23:09, schrieb Jason Baron:
> >>> While testing q35, I found that windows 7 (specifically, windows 7 ultimate
> >>> with sp1 x64), wouldn't install because it can't find the cdrom or disk drive.
> >>> The failure message is: 'A required cd/dvd device driver is missing. If you
> >>> have a driver floppy disk, CD, DVD, or USB flash drive, please insert it now.'
> >>> This can also be reproduced on piix by adding an ahci controller, and
> >>> observing that windows 7 does not see any devices behind it.
> >>> 
> >>> The problem is that when windows issues a HBA reset, qemu does not reset the
> >>> individual ports' PxCMD register. Windows 7 then reads back the PxCMD register
> >>> and presumably assumes that the ahci controller has already been initialized.
> >>> Windows then never sets up the PxIE register to enable interrupts, and thus it
> >>> never gets irqs back when it sends ata device inquiry commands.
> >>> 
> >>> I believe this change brings qemu into ahci 1.3 specification compliance.
> >>> 
> >>> Section 10.4.3 HBA Reset:
> >>> 
> >>> "
> >>> When GHC.HR is set to '1', GHC.AE, GHC.IE, the IS register, and all port
> >>> register fields (except PxFB/PxFBU/PxCLB/PxCLBU) that are not HwInit in the
> >>> HBA's register memory space are reset.
> >>> "
> >>> 
> >>> I've also re-tested Fedora 16 and 17 to verify that they continue to work with
> >>> this change.
> >>> 
> >>> Signed-off-by: Jason Baron <jbaron@redhat.com>
> >>> ---
> >>> hw/ide/ahci.c |    1 +
> >>> 1 files changed, 1 insertions(+), 0 deletions(-)
> >>> 
> >>> diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> >>> index 9fe89a5..06c236f 100644
> >>> --- a/hw/ide/ahci.c
> >>> +++ b/hw/ide/ahci.c
> >>> @@ -1199,6 +1199,7 @@ void ahci_reset(AHCIState *s)
> >>>         pr->irq_stat = 0;
> >>>         pr->irq_mask = 0;
> >>>         pr->scr_ctl = 0;
> >>> +        pr->cmd = 0;
> >>>         ahci_reset_port(s, i);
> >>>     }
> >>> }
> >>> 
> >> 
> >> In ahci_init() we have:
> >> 
> >>  ad->port_regs.cmd = PORT_CMD_SPIN_UP | PORT_CMD_POWER_ON;
> >> 
> >> Why is resetting to 0 in ahci_reset() correct? I think we can still get
> >> this part committed for 1.2 after you either explain why 0 is right or
> >> send a fixed version.
> >> 
> > 
> > Good catch. I just tried out the following instead in ahci_reset():
> > 
> > pr->cmd = PORT_CMD_SPIN_UP | PORT_CMD_POWER_ON;
> > 
> > And it continues to make Windows7 find the ahci disks. I'd like to do a
> > little more testing, but I will send an updated path.
> 
> Since we reset on init, we can just shove it there completely, right?
> 
> 

Actually, we don't call reset on init. I'm thinking for 1.2, we can just
add the fix to the reset path, and as Kevin suggested in 1.3, we will
look to add a call to ahci_reset() in the init path.

Thanks,

-Jason