linux-kernel - Re: [PATCH 2/3] input: alps: For protocol V3, do not process data when last packet's bit7 is set

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Date:	Fri, 3 Oct 2014 11:58:02 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Hans de Goede <hdegoede@...hat.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Yunkang Tang <yunkang.tang@...alps.com>,
	Tommy Will <tommywill2011@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] input: alps: For protocol V3, do not process data when last packet's bit7 is set

On Friday 03 October 2014 11:51:22 Hans de Goede wrote:
> Hi,
> 
> On 10/03/2014 11:43 AM, Pali Rohár wrote:
> > Sometimes laptops with closed lid receive invalid ALPS
> > protocol V3 packets with last bit7 set.
> > 
> > This happens on Dell Latitude laptops and it looks like it
> > is BIOS bug. Probably EC does not correctly split keyboard
> > and touchpad PS/2 data and when laptop lid is closed it
> > adds 0xFF packet into touchpad PS/2 data.
> > 
> > When last packet's bit7 is set it is invalid ALPS packet. So
> > Do not process it and drop it with PSMOUSE_FULL_PACKET.
> > 
> > After testing it looks like this patch fixed problem with
> > reseting mouse (after series of invalid packets) when
> > laptop lid is closed on Dell Latitude machines.
> > 
> > Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> > Tested-by: Pali Rohár <pali.rohar@...il.com>
> > ---
> > 
> >  drivers/input/mouse/alps.c |   10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/input/mouse/alps.c
> > b/drivers/input/mouse/alps.c index 1bd5aa1..b1f44d4 100644
> > --- a/drivers/input/mouse/alps.c
> > +++ b/drivers/input/mouse/alps.c
> > @@ -1179,6 +1179,16 @@ static psmouse_ret_t
> > alps_process_byte(struct psmouse *psmouse)
> > 
> >  		return PSMOUSE_BAD_DATA;
> >  	
> >  	}
> > 
> > +	if (priv->proto_version == ALPS_PROTO_V3 &&
> > psmouse->pktcnt == psmouse->pktsize) { +		// For protocol
> > V3, do not process data when last packet's bit7 is set
> > +		if (psmouse->packet[psmouse->pktcnt - 1] & 0x80) {
> > +			psmouse_dbg(psmouse, "v3 discard packet[%i] = 
%x\n",
> > +				    psmouse->pktcnt - 1,
> > +				    psmouse->packet[psmouse->pktcnt - 1]);
> > +			return PSMOUSE_FULL_PACKET;
> > +		}
> > +	}
> > +
> 
> I wonder if this should not be PSMOUSE_BAD_DATA as a return
> value ? I realize that with the 3th patch in place, that will
> cause an immediate reset, but if your theory is right that
> this ff gets inserted from the keyboard ps/2 stream, then we
> actually want a full reset as otherwise we will be out of
> sync then.
> 

We really do not know what is root cause of this problem. 
Probably it is BIOS/EC/firmware/... but it could be something 
other too.

On my laptop - Dell Latitude E6440 - I'm getting these invalid 
packets when I close LID. And they are generated too many (lot of 
per second). When PSMOUSE_FULL_PACKET is returned then no driver 
does not reset touchpad. With PSMOUSE_BAD_DATA psmouse decide 
that it needs reset and with 3rd patch psmouse could try to reset 
device too many times... So I think PSMOUSE_FULL_PACKET is better 
here. And having dmesg log full of device resets is probably not 
good too when laptop lid is closed.

> >  	/* Bytes 2 - pktsize should have 0 in the highest bit */
> >  	if ((priv->proto_version < ALPS_PROTO_V5) &&
> >  	
> >  	    psmouse->pktcnt >= 2 && psmouse->pktcnt <=
> >  	    psmouse->pktsize &&
> 
> Regards,
> 
> Hans

-- 
Pali Rohár
pali.rohar@...il.com

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