Re: i8042 access timings

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Tue, 25 Jan 2005 20:25:20 +0100, Vojtech Pavlik <vojtech@suse.cz> wrote:
> On Tue, Jan 25, 2005 at 02:17:33PM -0500, Dmitry Torokhov wrote:
> > On Tue, 25 Jan 2005 11:51:39 +0100, Andries Brouwer <aebr@win.tue.nl> wrote:
> > > On Tue, Jan 25, 2005 at 02:41:14AM -0500, Dmitry Torokhov wrote:
> > >
> > > > Recently there was a patch from Alan regarding access timing violations
> > > > in i8042. It made me curious as we only wait between accesses to status
> > > > register but not data register. I peeked into FreeBSD code and they use
> > > > delays to access both registers and I wonder if that's the piece that
> > > > makes i8042 mysteriously fail on some boards.
> > >
> > > You are following this much more closely than I do, but isn't the
> > > usual complaint "2.4 works, 2.6 fails"?
> > >
> >
> > Quite often it is but too much has changed in input layer to pinpoing
> > exact cause of the failure and I am open to any suggestions. Common
> > problems I see:
> >
> > 1. ACPI sometimes interferes with i8042, especially battery status
> > polling. I am concerned about embedded controller access as well, it
> > looks like it takes sweet time to read/write data to it and ec.c does
> > it with interrupts disabled.
> 
> Furthermore, the EC and the i8042 are often the same chip, resulting in
> the i8042 not answering when EC is busy. Enabling interrupts won't help.

It might or it might not, I think it really depends on firmware implementation.

> > Also, In 2.4 if BIOS detected PS/2 mouse we trusted it and did not do
> > any additional checks, now that i8042 is not x86 specific we do
> > everything by hand and it looks like some hardware is not expecting
> > it...
> 
> We may be able to loosen the checks again now that 98% of machines do
> have the PS/2 mouse port if they have the AT keyboard port.
> 

Maybe only for specific machines - the report was about a Toshiba and
it looks like they have quite a few problems with their KBCs -
bouncing keys, not being able to sustain full Synaptics 480 bytes/s
rate...

-- 
Dmitry