Re: [PATCH] ata.mod under qemu

[Christian Franke]

Pavel Roskin wrote:
> On Wed, 2009-05-20 at 23:40 +0200, Christian Franke wrote: 
>   
> > The attached patch should fix this. It should also prevents misleading 
> > error messages if a device does not exist.
> >     
> It helps detect CD-ROM under qemu.  But on the real hardware, it
> introduces ghost drives.
>
> Without the patch, I have (ata7) for the SATA hard drive.  With the
> patch, I have (ata7) for the SATA hard drive, (ata6) for the SATA DVD-RW
> and two bogus unreadable drives (ata0) and (ata1).
>
>   
Thanks for this test. I could not reproduce this yet. I presume that the 
controller behind (ata0) and (ata1) is the chipset's PATA controller.
If no device is connected, these controllers often echo a write to (e.g. 
command) register address back to the next read of (e.g. status) 
register address if the time between is too short. (No VM emulates this 
behavior :-)

Could you possibly repeat this test with 'debug=ata' enabled? If this 
removes the bogus drives, it is likely a problem of too short wait times.

I will prepare a new patch with longer timeouts and more thorough 
register tests during identify.

--
Regards,
Christian Franke