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

[Alexander Graf]

On 23.08.2012, at 23:09, Jason Baron wrote:

> 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.

What a nasty little bug. If it makes it work for you, the change is all fine 
from my POV (and should go into 1.2).

Thanks a lot for pulling off the effort to debug through all this. It sure 
must've been terribly hard.


Alex