Re: [Qemu-devel] Regression with floppy drive controller

[John Snow <jsnow@redhat.com>]

On 8/20/19 6:25 AM, Philippe Mathieu-Daudé wrote:
> [cross posting QEMU & SeaBIOS]
> 
> Hello,
> 
> I'v been looking at a QEMU bug report [1] which bisection resulted in a
> SeaBIOS commit:
> 
> 4a6dbcea3e412fe12effa2f812f50dd7eae90955 is the first bad commit
> commit 4a6dbcea3e412fe12effa2f812f50dd7eae90955
> Author: Nikolay Nikolov <nickysn@users.sourceforge.net>
> Date:   Sun Feb 4 17:27:01 2018 +0200
> 
>     floppy: Use timer_check() in floppy_wait_irq()
> 
>     Use timer_check() instead of using floppy_motor_counter in BDA for the
>     timeout check in floppy_wait_irq().
> 
>     The problem with using floppy_motor_counter was that, after it reaches
>     0, it immediately stops the floppy motors, which is not what is
>     supposed to happen on real hardware. Instead, after a timeout (like in
>     the end of every floppy operation, regardless of the result - success,
>     timeout or error), the floppy motors must be kept spinning for
>     additional 2 seconds (the FLOPPY_MOTOR_TICKS). So, now the
>     floppy_motor_counter is initialized to 255 (the max value) in the
>     beginning of the floppy operation. For IRQ timeouts, a different
>     timeout is used, specified by the new FLOPPY_IRQ_TIMEOUT constant
>     (currently set to 5 seconds - a fairly conservative value, but should
>     work reliably on most floppies).
> 
>     After the floppy operation, floppy_drive_pio() resets the
>     floppy_motor_counter to 2 seconds (FLOPPY_MOTOR_TICKS).
> 
>     This is also consistent with what other PC BIOSes do.
> 
> 
> This commit improve behavior with real hardware, so maybe QEMU is not
> modelling something or modelling it incorrectly?
> 
> 
> Regards,
> 
> Phil.
> 
> 
> PD: How to reproduce:
> 
> - Download Windows 98 SE floppy image from [2]
> 
> - Run QEMU using the 'isapc' machine:
> 
>   $ qemu-system-i386 -M isapc \
>      -fda Windows\ 98\ Second\ Edition\ Boot.img
> 
>   SeaBIOS (version rel-1.11.0-11-g4a6dbce-prebuilt.qemu.org)
>   Booting from Floppy...
>   Boot failed: could not read the boot disk
> 
> [1] https://bugs.launchpad.net/qemu/+bug/1840719
> [2] https://winworldpc.com/download/417d71c2-ae18-c39a-11c3-a4e284a2c3a5
> 

Well, that's unfortunate.

What version of QEMU shipped the SeaBIOS that caused the regression?