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

[Tomasz Chmielewski]

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)?


--
Tomasz Chmielewski
http://wpkg.org