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

[Alexander Graf <agraf@suse.de>]

On 30.08.2012, at 12:59, Jason Baron <jbaron@redhat.com> wrote:

> On Fri, Aug 24, 2012 at 06:39:02AM +0200, Alexander Graf 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).
>> 
> 
> Ok, I don't see it 1.2.0-rc2. If others are ok with this for 1.2, whose
> tree should this go through?

Kevin :)

Alex

> 
> Thanks,
> 
> -Jason