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[Qemu-devel] SATA CD-ROM booting failure with latest OVMF

From: Hannes Reinecke
Subject: [Qemu-devel] SATA CD-ROM booting failure with latest OVMF
Date: Fri, 03 Jul 2015 16:15:40 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0

Hi all,

I've updated OVMF to use the SATA controller, so that I could
finally use the Q35 machine specification with OVMF.

However, upon doing so I found that the (SATA) CD-ROM wouldn't work
anymore; directories on the CD-ROM can be read, but the file listing
contained only garbage.

After some _very_ tedious debugging I've found this to be an issue
with the ahci driver in qemu; ATAPI PIO transfers seem to be
slightly buggy. Enabling 'atapi_dma' transfers in atapi driver (even
for PIO mode) makes everything work again.

I still fail to see _why_ this is be the case; the logfiles
in both cases are pretty identical. Originally I thought that
somehow the big qemu lock plays a role here, but OVMF accesses
the ahci HBA only ever _after_ all transfers are complete.
And again, access patterns are identical in both cases.

So if anyone has another idea here ...


Dr. Hannes Reinecke                            zSeries & Storage
address@hidden                                 +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

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