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SubjectRe: 2.6 kernel won't reboot on AMD system - 8042 problem?
Sascha Wilde wrote:

>>> Is PS/2 supposed to support hotpluging at all? I guess it's not,
>>> but I may be wrong...
>> Yes it is, at least with newer (or rather not ancient) hardware...
> well, so the patch obviously can't be a final solution...

Yes, it doesn't strike me as being ideal.

More playing with the triple fault leads me to this:

static int i8042_command(unsigned char *param, int command)
unsigned long flags;
int retval = 0, i = 0;

spin_lock_irqsave(&i8042_lock, flags);

retval = i8042_wait_write();
if (!retval) {
dbg("%02x -> i8042 (command)", command & 0xff);
i8042_write_command(command & 0xff);

=====> A

if (!retval)
for (i = 0; i < ((command >> 12) & 0xf); i++) {
if ((retval = i8042_wait_write())) break;
dbg("%02x -> i8042 (parameter)", param[i]);

=====> B

Point 'B' is the "point of no reboot", at A we can still triple fault it
and get a nice normal reboot, so it's the parameter that it's writing
that it causing it to go funny.

I noticed something odd though... I reported this in another email:

*With keyboard* :

mice: PS/2 mouse device common for all mice
drivers/input/serio/i8042.c: 20 -> i8042 (command) [0]
drivers/input/serio/i8042.c: 65 <- i8042 (return) [0]

*Without keyboard* :

mice: PS/2 mouse device common for all mice
drivers/input/serio/i8042.c: fa <- i8042 (flush, aux) [0]
drivers/input/serio/i8042.c: 20 -> i8042 (command) [0]
drivers/input/serio/i8042.c: 9a <- i8042 (return) [0]

I noticed that
0x9a is the 'inverse' of 0x65. If I set it to 0x65 and write that out,
it still reboots afterwards! Hrm. I don't know what that means
exactly, but apparently it *is* possible to write something to the
controller and have it keep going.

Sascha, if you want to test it out, try this in i8042_controller_init,
at about line 724 (near this: i8042_initial_ctr = i8042_ctr;)

unsigned char pram;
pram = (~i8042_ctr) & 0xff ;
i8042_command(&pram, I8042_CMD_CTL_WCTR);

static struct
unsigned short size __attribute__ ((packed));
unsigned long long * base __attribute__ ((packed));
} no_idt = { 0, 0 };

__asm__ __volatile__("lidt %0": :"m" (no_idt));
__asm__ __volatile__("int3");

It reboots!

David N. Welton
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