lkml.org 
[lkml]   [2015]   [Apr]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] Add a quirk for the Dell XPS 13 (2015) when in PS/2 mode.
Date
On Wednesday 25 February 2015 21:45:22 Pali Rohár wrote:
> On Wednesday 25 February 2015 19:48:55 Mario Limonciello wrote:
> > On 02/20/2015 02:41 PM, Pali Rohár wrote:
> > > On Friday 20 February 2015 20:56:23 Mario Limonciello
> > > wrote:
> > >
> > > resetafter=0 means to never reset (even if driver receive
> > > e.g thousand invalid packets). I think this is very
> > > dangerous if there will be other bugs either in linux
> > > driver or some other HW problems.
> > >
> > > For ALPS issue I added resetafter = pktsize * 2 (Allow 2
> > > invalid packets without resetting device). Cannot you find
> > > something similar for synaptics touchpads on XPS? (pktsize
> > > for ALPS is 6, no idea how big are synaptics packets).
> >
> > Pali,
> >
> > I've done some experimentation with increasing the size to
> > resetafter to up to pktsize * 4. It will decrease the
> > number of occurrences of this problem, but the problem
> > still occurs eventually. pktsize for synaptics is 6 as
> > well. Would you recommend to continue to go higher than
> > that? Since out_of_sync_cnt is reset when a full packet
> > gets received, some arbitrarily high number should likely
> > fix it to.
> >
> > That being said, if you try to more closely follow what
> > Windows does for the mouse, it's not issuing a reconnect no
> > matter how much bad data is received.
>
> I believe problem is similar to one as with ALPS devices.
> Driver always receive 6 bytes packet of data (no new byte is
> inserted and no byte is never lost), just one byte in packet
> is incorrect (does not match specification).
>
> Setting resetafter to > 0 prevent problems when driver enters
> into undefined state (either by bug in driver of other SW/HW
> problem). So I think setting resetafter to 0 is not good idea.
>
> But if we know that setting resetafter to 4*pktsize is not
> enough (e.g. with experimenting you saw that driver received
> more then 4 invalid packets consecutively), set it to higher
> value.
>
> I think it is still good idea to ignore maximally as many
> packets which can be received in time which is equal to
> resetting device.
>
> E.g. when period of time in which we are dropping all packets
> is higher then time needed to reset touchpad, we should stop
> dropping packets and immediately reset touchpad. In this case
> we could hit maybe problem in driver (there can be bugs) or
> touchpad is in some bad state and out-of-sync...
>
> So if your tests show that there are never invalid 10 packets
> consecutively, then set resetafter to 10 packets. Value 10 is
> still not high and if it fix problem with touchpad I think it
> is acceptable. But rather ask Dmitry what he thinks about it.
> This is just my opinion.

Hello Mario,
have you patched synaptics driver with some resetafter parameter?
And have some team in dell found reason for invalid packets?

--
Pali Rohár
pali.rohar@gmail.com
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2015-04-11 01:21    [W:0.125 / U:0.264 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site