Re: i8042 access timings
From: Jaco Kroon
Date: Fri Jan 28 2005 - 09:22:13 EST
Vojtech Pavlik wrote:
On Thu, Jan 27, 2005 at 09:29:47PM +0100, Andries Brouwer wrote:
So what _might_ happen is that we write the command, and then
i8042_wait_write() thinks that there is space to write the data
immediately, and writes the data, but now the data got lost because the
buffer was busy.
Hmm - I just answered the same post and concluded that I didnt understand,
so you have progressed further. I considered the same possibility,
but the data was not lost since we read it again later.
Only the ready flag was lost.
What I believe is happening is that we're talking to SMM emulation of
the i8042, which doesn't have a clue about these commands, while the
underlying real hardware implementation does. And because of that they
disagree on what should happen when the command is issued, and since the
SMM emulation lazily synchronizes with the real HW, we only get the data
back with the next command.
I still don't have an explanation why both 'usb-handoff' and 'acpi=off'
help, I'd expect only the first to, but it might be related to the SCI
interrupt routing which isn't done when 'acpi=off'. Just a wild guess.
Ok, I'm not too clued up with recent hardware and the BIOS programming
that goes with it (being a system admin/application programmer), what
exactly is usb-handoff? acpi=off obviously just turns all acpi support
in the kernel off. SCI is also a new abbreviation I haven't seen
before. Whilst I've seen SMM before, I'm not sure what it stands for (I
assume it's something to do with simulation of legacy devices for older
operating systems)?
From the kernel-parameters documentation:
usb-handoff [HW] Enably early USB BIOS -> OS handoff
I guess this means the OS takes over control of the USB devices at an
earlier stage than usual - possibly before ACPI gets initialised? I'm
unable to determine much from looking at drivers/pci/quirks.c (which is
where the usb-handoff parameter is defined).
usb-handoff=1 does however also fix the problem. Ok. This makes it
even more confusing (and probably more complicated). The appropriate
section from dmesg that shows that it is working correctly:
i8042_init()
ACPI: PS/2 Keyboard Controller [KBC0] at I/O 0x60, 0x64, irq 1
ACPI: PS/2 Mouse Controller [MSE0] at irq 12
i8042_controller_init()
i8042_flush()
drivers/input/serio/i8042.c: 20 -> i8042 (command) [4]
drivers/input/serio/i8042.c: 47 <- i8042 (return) [4]
drivers/input/serio/i8042.c: 60 -> i8042 (command) [4]
drivers/input/serio/i8042.c: 56 -> i8042 (parameter) [4]
i8042_check_aux()
drivers/input/serio/i8042.c: Interrupt 12, without any data [8]
i8042_flush()
drivers/input/serio/i8042.c: d3 -> i8042 (command) [13]
drivers/input/serio/i8042.c: 5a -> i8042 (parameter) [13]
drivers/input/serio/i8042.c: a5 <- i8042 (return) [13]
i8042_check_aux: passed
So as with acpi=off, we get a correct return. Now that usb is
mentioned, I think either myself or Sebastian has mentioned that the
keyboard does not work unless USB1.1 support is compiled in. Another
clue possibly?
Another question - would it be usefull at all to see what happens if the
AUX_LOOP test is never performed but only AUX_TEST? Or does AUX_TEST
rely on the fact that AUX_LOOP must first fail/timeout somehow?
Jaco
--
There are only 10 kinds of people in this world,
those that understand binary and those that don't.
http://www.kroon.co.za/
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