geometry: Read LCHS from fw_cfg

Read bios geometry for boot devices from fw_cfg.

By receiving LCHS values directly from QEMU through fw_cfg we will be
able to support logical geometries which can not be inferred by SeaBIOS
(For instance: A 8GB virtio-blk hard drive which was originally created
as an IDE and must report LCHS of */32/63 for its operating system to
function will always break under SeaBIOS since a LARGE/LBA translation
will be used, causing the number of reported logical heads to be > 32.)

The only LCHS paravirtual interface available at the moment is for IDE
disks (rtc_read() in get_translation()) and it's limited to a maximum
of 4 disks (this code existed in SeaBIOS's translation function before
SCSI and VirtIO were even introduced).
This is why we create a new interface which allows passing LCHS
information per hdd.

Boot device information is serialized in the following way:
    * device_path lcyls lheads lsecs\n
    * device_path lcyls lheads lsecs\0

Device path is a null terminated string in the "Open Firmware" device
path format, the same path as used in bootorder.

Reviewed-by: Karl Heubaum <>
Reviewed-by: Arbel Moshe <>
Signed-off-by: Sam Eiderman <>
Message-Id: <>
1 file changed
tree: 7fabd96ed7b6ef0950c0d09ece4ecbcf95eaae74
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