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Re: [PATCH] ata.mod under qemu

From: Christian Franke
Subject: Re: [PATCH] ata.mod under qemu
Date: Thu, 21 May 2009 22:59:49 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20090403 SeaMonkey/1.1.16

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.

Christian Franke

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