linux-kernel - Re: [PATCH 4/7] Input: ALPS - Remove assumptions about packet size

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Date:	Mon, 31 Oct 2011 16:01:18 -0400
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Chase Douglas <chase.douglas@...onical.com>,
	Alessandro Rubini <rubini@...l.unipv.it>,
	Henrik Rydberg <rydberg@...omail.se>,
	Andrew Skalski <askalski@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] Input: ALPS - Remove assumptions about packet size

On Mon, Oct 31, 2011 at 11:24:37AM -0700, Dmitry Torokhov wrote:
> On Mon, Oct 31, 2011 at 02:17:02PM -0400, Seth Forshee wrote:
> > On Sun, Oct 30, 2011 at 11:36:19AM -0400, Chase Douglas wrote:
> > > On 10/26/2011 05:14 PM, Seth Forshee wrote:
> > > > In preparation for version 4 protocol support, which has 8-byte
> > > > data packets, remove all hard-coded assumptions about packet size
> > > > and use psmouse->pktsize instead.
> > > > 
> > > > Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
> > > > ---
> > > >  drivers/input/mouse/alps.c |   27 ++++++++++++++++++---------
> > > >  1 files changed, 18 insertions(+), 9 deletions(-)
> > > > 
> > > > diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
> > > > index 572cb21..14d1f64 100644
> > > > --- a/drivers/input/mouse/alps.c
> > > > +++ b/drivers/input/mouse/alps.c
> > > > @@ -315,7 +315,7 @@ static void alps_flush_packet(unsigned long data)
> > > >  
> > > >  	serio_pause_rx(psmouse->ps2dev.serio);
> > > >  
> > > > -	if (psmouse->pktcnt == 6) {
> > > > +	if (psmouse->pktcnt == psmouse->pktsize) {
> > > >  
> > > >  		/*
> > > >  		 * We did not any more data in reasonable amount of time.
> > > > @@ -365,15 +365,15 @@ static psmouse_ret_t alps_process_byte(struct psmouse *psmouse)
> > > >  		return PSMOUSE_BAD_DATA;
> > > >  	}
> > > >  
> > > > -	/* Bytes 2 - 6 should have 0 in the highest bit */
> > > > -	if (psmouse->pktcnt >= 2 && psmouse->pktcnt <= 6 &&
> > > > +	/* Bytes 2 - pktsize should have 0 in the highest bit */
> > > > +	if (psmouse->pktcnt >= 2 && psmouse->pktcnt <= psmouse->pktsize &&
> > > >  	    (psmouse->packet[psmouse->pktcnt - 1] & 0x80)) {
> > > >  		dbg("refusing packet[%i] = %x\n",
> > > >  		    psmouse->pktcnt - 1, psmouse->packet[psmouse->pktcnt - 1]);
> > > >  		return PSMOUSE_BAD_DATA;
> > > >  	}
> > > >  
> > > > -	if (psmouse->pktcnt == 6) {
> > > > +	if (psmouse->pktcnt == psmouse->pktsize) {
> > > >  		alps_process_packet(psmouse);
> > > >  		return PSMOUSE_FULL_PACKET;
> > > >  	}
> > > > @@ -531,8 +531,13 @@ static int alps_tap_mode(struct psmouse *psmouse, int enable)
> > > >  static int alps_poll(struct psmouse *psmouse)
> > > >  {
> > > >  	struct alps_data *priv = psmouse->private;
> > > > -	unsigned char buf[6];
> > > > +	unsigned char *buf;
> > > >  	bool poll_failed;
> > > > +	int ret = -1;
> > > > +
> > > > +	buf = kmalloc(psmouse->pktsize, GFP_KERNEL);
> > > > +	if (!buf)
> > > > +		return -1;
> > > 
> > > Can we preallocate a buffer somewhere instead of allocating every time
> > > we enter the function? If we know the maximum packet size we could
> > > allocate on the stack instead.
> > 
> > Thanks for pointing that out; I had meant to come back and do something
> > about this but forgot. I was hoping to avoid having to hard-code an
> > assumed maximum packet size. I'll take a look at it.
> 
> probably doing something like
> 
> 	unsigned char buf[sizeof(psmouse->packet)];
> 
> will cover it.

Yes, that will work great. I'll incorporate that into the next version
of the patches. Thanks.
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