On Tue, Feb 09, 2016 at 07:36:12PM +0100, Laszlo Ersek wrote: > On 02/09/16 17:22, John Snow wrote: > > On 02/09/2016 10:52 AM, Roman Kagan wrote: > >> On Mon, Feb 08, 2016 at 03:20:47PM -0500, John Snow wrote: > >>> On 02/08/2016 08:14 AM, Roman Kagan wrote: > >>>> On Fri, Feb 05, 2016 at 07:25:07PM +0100, Igor Mammedov wrote: > >>>>>> + aml_append(fdi, > >>>>>> + aml_int(cylinders - 1)); /* Maximum Cylinder Number */ > >>>>> this puts uint64_t(-1) in AML i.e. cylinders == 0 and overflow happens > >>>>> here > >>>>> > >>>>> CCing Jon > >>>> > >>>> I guess this is the effect of John's fdc rework. I used to think zero > >>>> geometry was impossible at the time this patch was developed. > >>>> > >>>> I wonder if it hasn't been fixed already by > >>>> > >>>> commit fd9bdbd3459e5b9d51534f0747049bc5b6145e07 > >>>> Author: John Snow <js...@redhat.com> > >>>> Date: Wed Feb 3 11:28:55 2016 -0500 > >>>> > >>>> fdc: fix detection under Linux > >>> > >>> Yes, hopefully solved on my end. The geometry values for an empty disk > >>> are not well defined (they certainly don't have any *meaning*) so if you > >>> are populating tables based on an empty drive, I just hope you also have > >>> the mechanisms needed to update said tables when the media changes. > >> > >> I don't. At the time the patch was developed there basically were no > >> mechanisms to update the geometry at all (and this was what you patchset > >> addressed, in particular, wasn't it?) so I didn't care. > >> > > > > That's not true. > > > > You could swap different 1.44MB-class diskettes for other geometries, > > check this out: > > > > static const FDFormat fd_formats[] = { > > /* First entry is default format */ > > /* 1.44 MB 3"1/2 floppy disks */ > > { FDRIVE_DRV_144, 18, 80, 1, FDRIVE_RATE_500K, }, > > { FDRIVE_DRV_144, 20, 80, 1, FDRIVE_RATE_500K, }, > > { FDRIVE_DRV_144, 21, 80, 1, FDRIVE_RATE_500K, }, > > { FDRIVE_DRV_144, 21, 82, 1, FDRIVE_RATE_500K, }, > > { FDRIVE_DRV_144, 21, 83, 1, FDRIVE_RATE_500K, }, > > { FDRIVE_DRV_144, 22, 80, 1, FDRIVE_RATE_500K, }, > > { FDRIVE_DRV_144, 23, 80, 1, FDRIVE_RATE_500K, }, > > { FDRIVE_DRV_144, 24, 80, 1, FDRIVE_RATE_500K, }, > > ... > > > > You absolutely could get different sector and track counts before my > > patchset. > > > > > >> Now if it actually has to be fully dynamic it's gonna be more > >> involved... > >> > >>> What do the guests use these values for? Are they fixed at boot? > >> > >> Only Windows guests use it so it's hard to tell. I can only claim that > >> if I stick bogus values into that ACPI object the guest fails to read > >> the floppy. > > We discussed this with John a bit on IRC. > > 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. Also, FWIW, SeaBIOS uses the standard 1.44MB floppy controller timing information even if a 5.25 drive is found - as far as I know this information is only ever used on PIO to the floppy controller and the QEMU floppy controller doesn't care what timing parameters it is programmed with. -Kevin