Re: mouse problems in 2.4.2 -> lost byte -> Patch(2.4.3)!

[Gunther Mayer]

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Original Problem: PS/2 mouse pointer goes upper right corner and stays there.
Diagnosis: one byte was lost and this is fatal for the mouse driver.

Various people wrote:
> 
> On Wed, Mar 28, 2001 at 05:19:33PM -0600, [e-mail] wrote:
..
> > > > > > > I am experiencing debilitating intermittent mouse problems & was about
> > > > > >
> > > > > > This is easily explained: some byte of the mouse protocol was lost.
> 
> Plus, it's very likely the new PS/2 code will break on some systems that
> have not-so-compatible i8042 chips, so it is really something that can't

Losing bytes on psaux is a bug!

We must first understand, how bytes can be lost (most probable first):
- transmission error on the line can easily happen in noisy environments
   and is _not_ handled correctly by linux (i.e. should do RESEND)
- 0xAA is always handled as reconnect, if the mouse generates this byte,
   Linux will de-sync the mouse driver
- Mouse is defective or keyboard controller defective
- An error in the linux kbd/mouse driver (e.g. triggered by X11<->console switching)

This patch printk's necessary information on the first 2 cases and
should be applied to the stable kernel, as this will help to resolve a severe bug !

Regards, Gunther

P.S.
These messages can be generated:
Apr  8 21:49:23 linux kernel: psaux: reconnect 0xAA detected
Apr  8 21:49:42 linux kernel: pc_keyb: mouse error (0x75), byte ignored(ff).
Apr  8 21:49:43 linux kernel: psaux: reconnect 0xAA detected

--- linux-2.4.3-orig/drivers/char/pc_keyb.c     Wed Apr  4 19:46:42 2001
+++ linux/drivers/char/pc_keyb.c        Sun Apr  8 21:45:37 2001
@@ -404,6 +404,11 @@
                mouse_reply_expected = 0;
        }
        else if(scancode == AUX_RECONNECT){
+               // Under normal operation most mice don't generate 0xAA.
+               // But, Other devices might be unusable with this policy.
+               //  (My mouse easily generates 0xAAs on rapid movements,
+               //   when set to 10 samples/sec.)
+               printk("psaux: reconnect detected(0xaa), sending AUX_ENABLE.\n");
                queue->head = queue->tail = 0;  /* Flush input queue */
                __aux_write_ack(AUX_ENABLE_DEV);  /* ping the mouse :) */
                return;
@@ -420,6 +425,9 @@
                        kill_fasync(&queue->fasync, SIGIO, POLL_IN);
                        wake_up_interruptible(&queue->proc_list);
                }
+               else
+                       // 2K buffer is enough for about 10 sec under normal operations, here.
+                       printk("psaux: buffer overflow, byte dropped.\n");
        }
 #endif
 }
@@ -465,6 +473,11 @@
                        else
                                handle_keyboard_event(scancode);
                }
+               else
+                       // Fixme: Ignoring bytes will de-sync mouse protocol.
+                       printk("pc_keyb: %s error (0x%02x), byte ignored(%02x).\n",
+                       (status & KBD_STAT_MOUSE_OBF)?"mouse":"kbd",status,scancode);
+
 
                status = kbd_read_status();
        }
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