linux-kernel - Re: [PATCH] Add a quirk for the Dell XPS 13 (2015) when in PS/2 mode.

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Date:	Fri, 10 Apr 2015 18:32:36 -0500
From:	Mario Limonciello <mario_limonciello@...l.com>
To:	Pali Rohár <pali.rohar@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>
Subject: Re: [PATCH] Add a quirk for the Dell XPS 13 (2015) when in PS/2 mode.


On 04/10/2015 06:14 PM, Pali Rohár wrote:
> On Saturday 11 April 2015 01:07:03 Mario Limonciello wrote:
> I could see problem with using older kernels which are in more
> stable or LTS distribution versions...
>
> But it is nice that problems are fixes for future 4.0/4.1
> versions.
>
> And if you located reason for invalid packets in PS/2 mode, will
> you fix it in some new bios versions?
>
> Can you comment if this is also same problem with invalid packets
> on E6440/E7440 machines?
>
Hi Pali,

For the XPS 13, yes earlier kernel versions will be affected, but we are encouraging users to run with 3.16+.  There are enough other issues with I2C touchpad, MST, HDA audio and other things that people will have a better experience on those kernels.  People who will install Ubuntu 14.04 LTS we will encourage to install the HWE stack that provides 3.16 or 3.19 instead.  Canonical is backporting fixes for I2C and HDA issues into these kernels already.

The root cause for the invalid packets in PS/2 mode on the XPS 13 is not fixable via a BIOS update.

The invalid packets on the Exx40 machines I believe is caused by some behavior that happens if the touchpad/trackstick receives data shortly after the internal keyboard was busy.  An interrupt is fired on the EC that will cause it discard data.  I think this is why it ends up on the other end looking like it does.
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