Re: [Qemu-devel] [SOLUTION] "i8042.c: No controller found" -> OS sees no keyboard if I type "in BIOS"

[Marcelo Tosatti]

On Wed, May 20, 2009 at 03:30:09PM +0200, Tomasz Chmielewski wrote:
> Tomasz Chmielewski schrieb:
>
>>> When I boot the guest and type (just hit any keys) in the VNC window  
>>> before the operating system boots, sometimes, the system loads with 
>>> no keyboard present - as signified in dmesg on guest:
>>>
>>> i8042.c: No controller found
>>>
>>> As a result, I can't use the keyboard in the VNC window.
>
>> drivers/input/serio/i8042.c in the Linux kerne has this:
>>
>> static int i8042_controller_check(void)
>> {
>>         if (i8042_flush() == I8042_BUFFER_SIZE) {
>>                 printk(KERN_ERR "i8042.c: No controller found.\n");
>>                 return -ENODEV;
>>         }
>>
>>         return 0;
>> }
>>
>>
>> So, can it be that if we type anything on keyboard (or move mouse) 
>> while Qemu's BIOS is still booting or later in the bootloader (GRUB, 
>> lilo), some buffer is not flushed and Linux gets confused? And as a 
>> result, decides there is no keyboard?
>
> Yes, this is what seems to happen - Qemu's keyboard buffer seems to be 
> infinite
> or at least very big; normal 8042 devices have buffer of 16 bytes only.
>
> If we add "i8042.debug" parameter to kernel command line,
> we will see how many characters were flushed during boot, i.e.:
>
>
> drivers/input/serio/i8042.c: ff <- i8042 (flush, aux) [0]
> drivers/input/serio/i8042.c: 18 <- i8042 (flush, aux) [0]
> drivers/input/serio/i8042.c: 92 <- i8042 (flush, aux) [0]
> drivers/input/serio/i8042.c: 00 <- i8042 (flush, aux) [0]
> (...)
>
>
> With this 16 byte buffer in drivers/input/serio/i8042.h (before 2.6.11 it was
> 32 bytes I think):
>
> #define I8042_BUFFER_SIZE       16
>
>
> and this piece of code in drivers/input/serio/i8042.c:
>
>
> /*
> * i8042_flush() flushes all data that may be in the keyboard and mouse buffers
> * of the i8042 down the toilet.
> */
>
> static int i8042_flush(void)
> {
>        unsigned long flags;
>        unsigned char data, str;
>        int i = 0;
>
>        spin_lock_irqsave(&i8042_lock, flags);
>
>        while (((str = i8042_read_status()) & I8042_STR_OBF) && (i < 
> I8042_BUFFER_SIZE)) {
>                udelay(50);
>                data = i8042_read_data();
>                i++;
>                dbg("%02x <- i8042 (flush, %s)", data,
>                        str & I8042_STR_AUXDATA ? "aux" : "kbd");
>        }
>
>        spin_unlock_irqrestore(&i8042_lock, flags);
>
>        return i;
> }
>
>
>
> Linux kernel thinks there is no controller:
>
>
> (...)
> drivers/input/serio/i8042.c: 28 <- i8042 (flush, aux) [0]
> drivers/input/serio/i8042.c: 00 <- i8042 (flush, aux) [0]
> i8042.c: No controller found.
>
>
> If we increase "I8042_BUFFER_SIZE" to 256 or more, we have a much better 
> chance that a booted Linux will have a keyboard present.
>
> So, who's to be blamed?
>
> Linux kernel for having its i8042 buffer to small (16 bytes), fixable with:
>
>
> --- i8042.h.orig        2009-05-20 15:26:32.000000000 +0200
> +++ i8042.h     2009-05-20 15:26:32.000000000 +0200
> @@ -73,7 +73,7 @@
>  * the i8042 buffers.
>  */
>
> -#define I8042_BUFFER_SIZE      16
> +#define I8042_BUFFER_SIZE      256
>
> /*
>  * Number of AUX ports on controllers supporting active multiplexing
>
>
>
> Or Qemu, for having its keyboard buffer too large (I'm not sure, but probably 
> 256 bytes)?

All references (*) i could find mention 16 bytes of output buffer
(including the Linux source as you mentioned, which was reduced from 32
to 16 somewhere in the 2.6.10 era).

http://www.computer-engineering.org/ps2protocol/

http://linux.bkbits.net:8080/linux-2.6.28-stable/drivers/input/serio/i8042.h?PAGE=diffs&REV=4203735dp_doSExYU6ido8KnczbjzQ

Reducing PS2_QUEUE_SIZE to 16 also makes the Linux detection loop happy.

If QEMU claims to emulate i8042, it should be similar to real hardware.

However i'm not familiar with PS/2 or i8042. Anthony?