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Date: Wed, 17 Feb 2016 17:31:03 +0300
From: Roman Kagan <rkagan@virtuozzo.com>
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Subject: Re: [Qemu-devel] [PULL 48/49] i386: populate floppy drive
 information in DSDT
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Eduardo Habkost <ehabkost@redhat.com>, John Snow <jsnow@redhat.com>, qemu-devel@nongnu.org, Kevin O'Connor <kevin@koconnor.net>, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Laszlo Ersek <lersek@redhat.com>, Richard Henderson <rth@twiddle.net>

On Sun, Feb 14, 2016 at 05:02:14PM +0200, Michael S. Tsirkin wrote:
> On Sat, Feb 13, 2016 at 12:26:53PM -0500, Kevin O'Connor wrote:
> > On Tue, Feb 09, 2016 at 07:36:12PM +0100, Laszlo Ersek wrote:
> > > In my opinion, the real mess in this case is in the ACPI spec itself. If
> > > you re-read the _FDI control method's description, the Package that it
> > > returns contains *dynamic* geometry data, about the *disk* (not *drive*):
> > > 
> > > - Maximum Cylinder Number // Integer (WORD)
> > > - Maximum Sector Number   // Integer (WORD)
> > > - Maximum Head Number     // Integer (WORD)
> > 
> > FWIW, that's not how I read the ACPI specification.  I read it as
> > saying that the information should be filled with the maximum number
> > of CHS that the drive can support.  So, even if a smaller disk happens
> > to be in the drive the maximum the drive supports would not change.
> 
> I agree. It says:
> 	This object returns information about a floppy disk drive. This
> 	information is the same as
> 	that returned by the INT 13 Function 08H on Intel Architecture PCs.
> 
> So disk drive, not disk information.
> 
> And FWIW I have an old "the undocumented PC" book which says
> this about int 13h function 8 (read diskette drive parameters):
> 
> "Remember this data is *not* the limits of the media in the drive,
> but the maximum capability of the specified drive".

Thanks for the info, I've re-implemented the patchset according to it
and Windows guests (w2k12, w10) seem to be happy with it, including
dynamically (re-)inserting the "diskette" of compatible size.

I'll submit the patches shortly.

Thanks,
Roman.