[Qemu-devel] Re: [PATCH] No keyboard / mouse after reboot

["Dinesh Subhraveti" <subhraveti@gmail.com>]

"Anthony Liguori" <anthony@codemonkey.ws> wrote in message 
news:4A5BDB00.8030100@codemonkey.ws...
> Needs a Signed-off-by.  However...
>
> Dinesh Subhraveti wrote:
>> At system initialization, some guests conclude that i8042 controller is 
>> missing when the PS2 buffer is full.  As a result, the guest comes up 
>> with no keyboard or mouse.  The behavior is seen when the user types or 
>> mouses over the VNC window during the BIOS phase of a reboot, causing the 
>> PS2 buffer to fill up.  It doesn't occur when the system boots the first 
>> time, since the device is initially disabled and doesn't accept events.
>>  This patch tunes Qemu parameters to reasonable values which make the 
>> guest happy.  Linux assumes the size of PS2 buffer to be 16 bytes, while 
>> Qemu defines it as 256.  Reducing PS2_QUEUE_SIZE to 15 ensures that the 
>> guest never sees the buffer to be full.
>
> Why is Linux making assumptions about queue size being 16?  It sounds

Good question, for which I don't know the answer.  But regardless of the 
buffer size, it fills up quite quickly with mouse events, and the guest 
would be left without a keyboard.

> broken to me.  In fact, I looked in one of my PC hardware books and it 
> claims that the typical KBD buffer size is around 20 bytes so if Linux is 
> assuming 16, it's definitely broken.
>
> But there's speculation in the previous thread that we're masking a BIOS 
> bug.  Has that been ruled out?
>

Yeah, this doesn't seem to be a BIOS issue.  It is also reproducible 
with -kernel option.

Thanks,
Dinesh