[PATCH v3 2/4] input: alps: Allow 2 invalid packets without resetting device

["Pali Rohár" <pali.rohar@gmail.com>]

On some Dell Latitude laptops ALPS device or Dell EC send one invalid byte in
6 bytes ALPS packet. In this case psmouse driver enter out of sync state. It
looks like that all other bytes in packets are valid and also device working
properly. So there is no need to do full device reset, just need to wait
for byte which match condition for first byte (start of packet). Because ALPS
packets are bigger (6 or 8 bytes) default limit is small.

This patch increase number of invalid bytes to size of 2 ALPS packets which
psmouse driver can drop before do full reset.

Resetting ALPS devices take some time and when doing reset on some Dell laptops
touchpad, trackstick and also keyboard do not respond. So it is better to do it
only if really necessary.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Pali Rohár <pali.rohar@gmail.com>
Cc: stable@vger.kernel.org
---
 drivers/input/mouse/alps.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
index a772745..7c47e97 100644
--- a/drivers/input/mouse/alps.c
+++ b/drivers/input/mouse/alps.c
@@ -2391,6 +2391,9 @@ int alps_init(struct psmouse *psmouse)
 	/* We are having trouble resyncing ALPS touchpads so disable it for now */
 	psmouse->resync_time = 0;
 
+	/* Allow 2 invalid packets without resetting device */
+	psmouse->resetafter = psmouse->pktsize * 2;
+
 	return 0;
 
 init_fail:
-- 
1.7.9.5