linux-kernel - [PATCH 3.2 102/110] Input: usbtouchscreen - avoid unresponsive TSC-30 touch screen

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Message-ID: <lsq.1439201551.713057610@decadent.org.uk>
Date:	Mon, 10 Aug 2015 12:12:31 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Jakob Mustafa" <jakob.mustafa@...ecmed.com>,
	"Dmitry Torokhov" <dmitry.torokhov@...il.com>,
	"Bernhard Bender" <bernhard.bender@...ecmed.com>
Subject: [PATCH 3.2 102/110] Input: usbtouchscreen - avoid unresponsive
 TSC-30 touch screen

3.2.71-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Bernhard Bender <bernhard.bender@...ecmed.com>

commit 968491709e5b1aaf429428814fff3d932fa90b60 upstream.

This patch fixes a problem in the usbtouchscreen driver for DMC TSC-30
touch screen.  Due to a missing delay between the RESET and SET_RATE
commands, the touch screen may become unresponsive during system startup or
driver loading.

According to the DMC documentation, a delay is needed after the RESET
command to allow the chip to complete its internal initialization. As this
delay is not guaranteed, we had a system where the touch screen
occasionally did not send any touch data. There was no other indication of
the problem.

The patch fixes the problem by adding a 150ms delay between the RESET and
SET_RATE commands.

Suggested-by: Jakob Mustafa <jakob.mustafa@...ecmed.com>
Signed-off-by: Bernhard Bender <bernhard.bender@...ecmed.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/input/touchscreen/usbtouchscreen.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/input/touchscreen/usbtouchscreen.c
+++ b/drivers/input/touchscreen/usbtouchscreen.c
@@ -528,6 +528,9 @@ static int dmc_tsc10_init(struct usbtouc
 		goto err_out;
 	}

+	/* TSC-25 data sheet specifies a delay after the RESET command */
+	msleep(150);
+
 	/* set coordinate output rate */
 	buf[0] = buf[1] = 0xFF;
 	ret = usb_control_msg(dev, usb_rcvctrlpipe (dev, 0),

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