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

[Kevin Wolf <kwolf@redhat.com>]

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.

I think for 1.3 there's still a bit more left. We're missing some more
fields in a reset: tfdata isn't set at all, should be set to 0x7f in
ahci_reset_port(), and cmd_issue should be set to 0. And shouldn't
ahci_init() actually call ahci_reset() in order to ensure consistent
results?

Kevin