linux-kernel - Re: [PATCH] Disable i8042 checks on Intel Apple Macs

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Date:	Mon, 25 Jan 2010 14:30:04 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Vojtech Pavlik <vojtech@...e.cz>,
	Robert Hancock <hancockrwd@...il.com>,
	Bastien Nocera <hadess@...ess.net>,
	linux-kernel <linux-kernel@...r.kernel.org>, pjones@...hat.com
Subject: Re: [PATCH] Disable i8042 checks on Intel Apple Macs

On Mon, Jan 25, 2010 at 02:18:40PM -0800, H. Peter Anvin wrote:
> On 01/25/2010 02:15 PM, Dmitry Torokhov wrote:
> > On Mon, Jan 25, 2010 at 01:32:42PM -0800, H. Peter Anvin wrote:
> >> On 01/25/2010 08:34 AM, Vojtech Pavlik wrote:
> >>>
> >>> Thus I believe that the right fix here is to figure out why the accesses
> >>> to the ports 0x60/0x64 take a long time or forever on a Mac. Is it just
> >>> that the kernel is timing out waiting for the i8042? Or is it something
> >>> more sinister?
> >>>
> >>
> >> In the A20 code in the setup code, I look for 0xFF coming back and
> >> terminate the "wait for ready" loop much sooner than for other values.
> >> 0xFF is a *possible* status value, but not a very *likely* one
> >> (especially for repeated reads), as it would represent:
> >>
> >> parity error + receive timeout + transmit timeout + keyboard lock +
> >> command + selftest OK + input full + output full.
> >>
> > 
> > You allow up to 32 0xFFs while i8042 driver does maximum 16 reads of
> > whatever - if OBF is still raised we assume i8042 is not there. Does
> > that mean that reads from 0x60 is what hurts on Macs?
> > 
> > Bastien, could you try modifying drivers/input/serio/i8042.c::
> > i8042_flush() to not call i8042_read_data() when str is 0xff and see if
> > it helps with lockups?
> > 
> 
> We should never read from port 0x60 unless bit 1 in port 0x64 is set.
> Do we do that?

No, we don't read of OBF is 0. Incidentially 0xff has it set ;) so we do
try reading data port.

-- 
Dmitry
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