Subject: [PATCH 2/3 V2] iio: mxs: Implement support for touchscreen

From: [email-masked] (Marek Vasut)
Date: Wed, 19 Dec 2012 18:01:31 +0100

Ccing Dmitry.

Also, Jonathan, can I get your review please?

> This patch implements support for sampling of a touchscreen into
> the MXS LRADC driver. The LRADC block allows configuring some of
> it's channels into special mode where they either output the drive
> voltage or sample it, allowing it to operate a 4-wire or 5-wire
> resistive touchscreen.
> 
> In case the touchscreen mode is enabled, the LRADC slot #7 is
> reserved for touchscreen only, therefore it is not possible to
> sample 8 LRADC channels at time, but only 7 channels.
> 
> The touchscreen controller is configured such that the PENDOWN event
> disables touchscreen interrupts and triggers execution of worker
> thread, which then polls the touchscreen controller for X, Y and
> Pressure values. This reduces the overhead of interrupt-driven
> operation. Upon the PENUP event, the worker thread re-enables the
> PENDOWN detection interrupt and exits.
> 
> Signed-off-by: Marek Vasut <[email-masked]>
> Cc: Fabio Estevam <[email-masked]>
> Cc: Jonathan Cameron <[email-masked]>
> Cc: Shawn Guo <[email-masked]>
> ---
>  .../bindings/staging/iio/adc/mxs-lradc.txt         |    6 +
>  drivers/staging/iio/adc/mxs-lradc.c                |  469
> +++++++++++++++++++- 2 files changed, 454 insertions(+), 21 deletions(-)
> 
> V2: - Replace the use_touchscreen* with enum mxs_lradc_ts, which now tracks
>       touchscreen state (OFF, 4-wire, 5-wire)
>     - Add "stop_touchscreen" bit, which indicates the touchscreen is going
> down and makes the driver not re-enable touchscreen interrupts and start
> any new touchscreen works.
>     - Make all bitfields "unsigned int" instead of plain "int"
>     - Use switch(plate) in mxs_lradc_ts_sample()
>     - Cancel touchscreen thread in mxs_lradc_ts_close(), do this only after
>       we are sure touchscreen interrupt is off and will never be
> re-enabled. This avoids serious race condition.
>     - Call input_free_device() if input_register_device() fails to avoid
> memory leak.
>     - Do not call input_free_device() after input_unregister_device() in
>       mxs_lradc_ts_unregister() to avoid double-free
> 
> diff --git
> a/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt
> b/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt index
> 801d58c..4688205 100644
> --- a/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt
> +++ b/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt
> @@ -5,6 +5,12 @@ Required properties:
>  - reg: Address and length of the register set for the device
>  - interrupts: Should contain the LRADC interrupts
> 
> +Optional properties:
> +- fsl,lradc-touchscreen-wires: Number of wires used to connect the
> touchscreen +                               to LRADC. Valid value is
> either 4 or 5. If this +                               property is not
> present, then the touchscreen is +                               disabled.
> +
>  Examples:
> 
>  	lradc at 80050000 {
> diff --git a/drivers/staging/iio/adc/mxs-lradc.c
> b/drivers/staging/iio/adc/mxs-lradc.c index 6249957..52317ef 100644
> --- a/drivers/staging/iio/adc/mxs-lradc.c
> +++ b/drivers/staging/iio/adc/mxs-lradc.c
> @@ -32,6 +32,8 @@
>  #include <linux/stmp_device.h>
>  #include <linux/bitops.h>
>  #include <linux/completion.h>
> +#include <linux/delay.h>
> +#include <linux/input.h>
> 
>  #include <mach/mxs.h>
>  #include <mach/common.h>
> @@ -59,6 +61,21 @@
>  #define LRADC_DELAY_TIMER_PER	200
>  #define LRADC_DELAY_TIMER_LOOP	5
> 
> +/*
> + * Once the pen touches the touchscreen, the touchscreen switches from
> + * IRQ-driven mode to polling mode to prevent interrupt storm. The polling
> + * is realized by worker thread, which is called every 20 or so
> milliseconds. + * This gives the touchscreen enough fluence and does not
> strain the system + * too much.
> + */
> +#define LRADC_TS_SAMPLE_DELAY_MS	5
> +
> +/*
> + * The LRADC reads the following amount of samples from each touchscreen
> + * channel and the driver then computes avarage of these.
> + */
> +#define LRADC_TS_SAMPLE_AMOUNT		4
> +
>  static const char * const mxs_lradc_irq_name[] = {
>  	"mxs-lradc-touchscreen",
>  	"mxs-lradc-thresh0",
> @@ -75,6 +92,12 @@ static const char * const mxs_lradc_irq_name[] = {
>  	"mxs-lradc-button1",
>  };
> 
> +enum mxs_lradc_ts {
> +	MXS_LRADC_TOUCHSCREEN_NONE = 0,
> +	MXS_LRADC_TOUCHSCREEN_4WIRE,
> +	MXS_LRADC_TOUCHSCREEN_5WIRE,
> +};
> +
>  struct mxs_lradc {
>  	struct device		*dev;
>  	void __iomem		*base;
> @@ -86,21 +109,69 @@ struct mxs_lradc {
>  	struct mutex		lock;
> 
>  	struct completion	completion;
> +
> +	/*
> +	 * Touchscreen LRADC channels receives a private slot in the CTRL4
> +	 * register, the slot #7. Therefore only 7 slots instead of 8 in the
> +	 * CTRL4 register can be mapped to LRADC channels when using the
> +	 * touchscreen.
> +	 *
> +	 * Furthermore, certain LRADC channels are shared between touchscreen
> +	 * and/or touch-buttons and generic LRADC block. Therefore when using
> +	 * either of these, these channels are not available for the regular
> +	 * sampling. The shared channels are as follows:
> +	 *
> +	 * CH0 -- Touch button #0
> +	 * CH1 -- Touch button #1
> +	 * CH2 -- Touch screen XPUL
> +	 * CH3 -- Touch screen YPLL
> +	 * CH4 -- Touch screen XNUL
> +	 * CH5 -- Touch screen YNLR
> +	 * CH6 -- Touch screen WIPER (5-wire only)
> +	 *
> +	 * The bitfields below represents which parts of the LRADC block are
> +	 * switched into special mode of operation. These channels can not
> +	 * be sampled as regular LRADC channels. The driver will refuse any
> +	 * attempt to sample these channels.
> +	 */
> +#define CHAN_MASK_TOUCHBUTTON		(0x3 << 0)
> +#define CHAN_MASK_TOUCHSCREEN_4WIRE	(0xf << 2)
> +#define CHAN_MASK_TOUCHSCREEN_5WIRE	(0x1f << 2)
> +	enum mxs_lradc_ts	use_touchscreen;
> +	unsigned int		stop_touchscreen:1;
> +	unsigned int		use_touchbutton:1;
> +
> +	struct input_dev	*ts_input;
> +	struct work_struct	ts_work;
>  };
> 
>  #define	LRADC_CTRL0				0x00
> -#define LRADC_CTRL0_TOUCH_DETECT_ENABLE		(1 << 23)
> -#define LRADC_CTRL0_TOUCH_SCREEN_TYPE		(1 << 22)
> +#define	LRADC_CTRL0_TOUCH_DETECT_ENABLE		(1 << 23)
> +#define	LRADC_CTRL0_TOUCH_SCREEN_TYPE		(1 << 22)
> +#define	LRADC_CTRL0_YNNSW	/* YM */	(1 << 21)
> +#define	LRADC_CTRL0_YPNSW	/* YP */	(1 << 20)
> +#define	LRADC_CTRL0_YPPSW	/* YP */	(1 << 19)
> +#define	LRADC_CTRL0_XNNSW	/* XM */	(1 << 18)
> +#define	LRADC_CTRL0_XNPSW	/* XM */	(1 << 17)
> +#define	LRADC_CTRL0_XPPSW	/* XP */	(1 << 16)
> +#define	LRADC_CTRL0_PLATE_MASK			(0x3f << 16)
> 
>  #define	LRADC_CTRL1				0x10
> -#define	LRADC_CTRL1_LRADC_IRQ(n)		(1 << (n))
> -#define	LRADC_CTRL1_LRADC_IRQ_MASK		0x1fff
> +#define	LRADC_CTRL1_TOUCH_DETECT_IRQ_EN		(1 << 24)
>  #define	LRADC_CTRL1_LRADC_IRQ_EN(n)		(1 << ((n) + 16))
>  #define	LRADC_CTRL1_LRADC_IRQ_EN_MASK		(0x1fff << 16)
> +#define	LRADC_CTRL1_LRADC_IRQ_EN_OFFSET		16
> +#define	LRADC_CTRL1_TOUCH_DETECT_IRQ		(1 << 8)
> +#define	LRADC_CTRL1_LRADC_IRQ(n)		(1 << (n))
> +#define	LRADC_CTRL1_LRADC_IRQ_MASK		0x1fff
> +#define	LRADC_CTRL1_LRADC_IRQ_OFFSET		0
> 
>  #define	LRADC_CTRL2				0x20
>  #define	LRADC_CTRL2_TEMPSENSE_PWD		(1 << 15)
> 
> +#define	LRADC_STATUS				0x40
> +#define	LRADC_STATUS_TOUCH_DETECT_RAW		(1 << 0)
> +
>  #define	LRADC_CH(n)				(0x50 + (0x10 * (n)))
>  #define	LRADC_CH_ACCUMULATE			(1 << 29)
>  #define	LRADC_CH_NUM_SAMPLES_MASK		(0x1f << 24)
> @@ -132,6 +203,7 @@ static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
>  {
>  	struct mxs_lradc *lradc = iio_priv(iio_dev);
>  	int ret;
> +	unsigned long mask;
> 
>  	if (m != IIO_CHAN_INFO_RAW)
>  		return -EINVAL;
> @@ -140,6 +212,12 @@ static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
>  	if (chan->channel > LRADC_MAX_TOTAL_CHANS)
>  		return -EINVAL;
> 
> +	/* Validate the channel if it doesn't intersect with reserved chans. */
> +	bitmap_set(&mask, chan->channel, 1);
> +	ret = iio_validate_scan_mask_onehot(iio_dev, &mask);
> +	if (ret)
> +		return -EINVAL;
> +
>  	/*
>  	 * See if there is no buffered operation in progess. If there is, simply
>  	 * bail out. This can be improved to support both buffered and raw IO at
> @@ -161,7 +239,11 @@ static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
>  		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);
>  	writel(0xff, lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);
> 
> -	writel(chan->channel, lradc->base + LRADC_CTRL4);
> +	/* Clean the slot's previous content, then set new one. */
> +	writel(LRADC_CTRL4_LRADCSELECT_MASK(0),
> +		lradc->base + LRADC_CTRL4 + STMP_OFFSET_REG_CLR);
> +	writel(chan->channel, lradc->base + LRADC_CTRL4 + STMP_OFFSET_REG_SET);
> +
>  	writel(0, lradc->base + LRADC_CH(0));
> 
>  	/* Enable the IRQ and start sampling the channel. */
> @@ -195,6 +277,272 @@ static const struct iio_info mxs_lradc_iio_info = {
>  };
> 
>  /*
> + * Touchscreen handling
> + */
> +enum lradc_ts_plate {
> +	LRADC_SAMPLE_X,
> +	LRADC_SAMPLE_Y,
> +	LRADC_SAMPLE_PRESSURE,
> +};
> +
> +static int mxs_lradc_ts_touched(struct mxs_lradc *lradc)
> +{
> +	uint32_t reg;
> +
> +	/* Enable touch detection. */
> +	writel(LRADC_CTRL0_PLATE_MASK,
> +		lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);
> +	writel(LRADC_CTRL0_TOUCH_DETECT_ENABLE,
> +		lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_SET);
> +
> +	msleep(LRADC_TS_SAMPLE_DELAY_MS);
> +
> +	reg = readl(lradc->base + LRADC_STATUS);
> +
> +	return reg & LRADC_STATUS_TOUCH_DETECT_RAW;
> +}
> +
> +static int32_t mxs_lradc_ts_sample(struct mxs_lradc *lradc,
> +				enum lradc_ts_plate plate, int change)
> +{
> +	unsigned long delay, jiff;
> +	uint32_t reg, ctrl0 = 0, chan = 0;
> +	/* The touchscreen always uses CTRL4 slot #7. */
> +	const uint8_t slot = 7;
> +	uint32_t val;
> +
> +	/*
> +	 * There are three correct configurations of the controller sampling
> +	 * the touchscreen, each of these configuration provides different
> +	 * information from the touchscreen.
> +	 *
> +	 * The following table describes the sampling configurations:
> +	 * +-------------+-------+-------+-------+
> +	 * | Wire \ Axis |   X   |   Y   |   Z   |
> +	 * +---------------------+-------+-------+
> +	 * |   X+ (CH2)  |   HI  |   TS  |   TS  |
> +	 * +-------------+-------+-------+-------+
> +	 * |   X- (CH4)  |   LO  |   SH  |   HI  |
> +	 * +-------------+-------+-------+-------+
> +	 * |   Y+ (CH3)  |   SH  |   HI  |   HI  |
> +	 * +-------------+-------+-------+-------+
> +	 * |   Y- (CH5)  |   TS  |   LO  |   SH  |
> +	 * +-------------+-------+-------+-------+
> +	 *
> +	 * HI ... strong '1'  ; LO ... strong '0'
> +	 * SH ... sample here ; TS ... tri-state
> +	 *
> +	 * There are a few other ways of obtaining the Z coordinate
> +	 * (aka. pressure), but the one in the table seems to be the
> +	 * most reliable one.
> +	 */
> +	switch (plate) {
> +	case LRADC_SAMPLE_X:
> +		ctrl0 = LRADC_CTRL0_XPPSW | LRADC_CTRL0_XNNSW;
> +		chan = 3;
> +		break;
> +	case LRADC_SAMPLE_Y:
> +		ctrl0 = LRADC_CTRL0_YPPSW | LRADC_CTRL0_YNNSW;
> +		chan = 4;
> +		break;
> +	case LRADC_SAMPLE_PRESSURE:
> +		ctrl0 = LRADC_CTRL0_YPPSW | LRADC_CTRL0_XNNSW;
> +		chan = 5;
> +		break;
> +	}
> +
> +	if (change) {
> +		writel(LRADC_CTRL0_PLATE_MASK,
> +			lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);
> +		writel(ctrl0, lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_SET);
> +
> +		writel(LRADC_CTRL4_LRADCSELECT_MASK(slot),
> +			lradc->base + LRADC_CTRL4 + STMP_OFFSET_REG_CLR);
> +		writel(chan << LRADC_CTRL4_LRADCSELECT_OFFSET(slot),
> +			lradc->base + LRADC_CTRL4 + STMP_OFFSET_REG_SET);
> +	}
> +
> +	writel(0xffffffff, lradc->base + LRADC_CH(slot) + STMP_OFFSET_REG_CLR);
> +	writel(1 << slot, lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_SET);
> +
> +	delay = jiffies + msecs_to_jiffies(LRADC_TS_SAMPLE_DELAY_MS);
> +	do {
> +		jiff = jiffies;
> +		reg = readl_relaxed(lradc->base + LRADC_CTRL1);
> +		if (reg & LRADC_CTRL1_LRADC_IRQ(slot))
> +			break;
> +	} while (time_before(jiff, delay));
> +
> +	writel(LRADC_CTRL1_LRADC_IRQ(slot),
> +		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);
> +
> +	if (time_after_eq(jiff, delay))
> +		return -ETIMEDOUT;
> +
> +	val = readl(lradc->base + LRADC_CH(slot));
> +	val &= LRADC_CH_VALUE_MASK;
> +
> +	return val;
> +}
> +
> +static int32_t mxs_lradc_ts_sample_filter(struct mxs_lradc *lradc,
> +				enum lradc_ts_plate plate)
> +{
> +	int32_t val, tot = 0;
> +	int i;
> +
> +	val = mxs_lradc_ts_sample(lradc, plate, 1);
> +
> +	/* Delay a bit so the touchscreen is stable. */
> +	mdelay(2);
> +
> +	for (i = 0; i < LRADC_TS_SAMPLE_AMOUNT; i++) {
> +		val = mxs_lradc_ts_sample(lradc, plate, 0);
> +		tot += val;
> +	}
> +
> +	return tot / LRADC_TS_SAMPLE_AMOUNT;
> +}
> +
> +static void mxs_lradc_ts_work(struct work_struct *ts_work)
> +{
> +	struct mxs_lradc *lradc = container_of(ts_work,
> +				struct mxs_lradc, ts_work);
> +	int val_x, val_y, val_p;
> +	bool valid = false;
> +
> +	while (mxs_lradc_ts_touched(lradc)) {
> +		/* Disable touch detector so we can sample the touchscreen. */
> +		writel(LRADC_CTRL0_TOUCH_DETECT_ENABLE,
> +			lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);
> +
> +		if (likely(valid)) {
> +			input_report_abs(lradc->ts_input, ABS_X, val_x);
> +			input_report_abs(lradc->ts_input, ABS_Y, val_y);
> +			input_report_abs(lradc->ts_input, ABS_PRESSURE, val_p);
> +			input_report_key(lradc->ts_input, BTN_TOUCH, 1);
> +			input_sync(lradc->ts_input);
> +		}
> +
> +		valid = false;
> +
> +		val_x = mxs_lradc_ts_sample_filter(lradc, LRADC_SAMPLE_X);
> +		if (val_x < 0)
> +			continue;
> +		val_y = mxs_lradc_ts_sample_filter(lradc, LRADC_SAMPLE_Y);
> +		if (val_y < 0)
> +			continue;
> +		val_p = mxs_lradc_ts_sample_filter(lradc, 
LRADC_SAMPLE_PRESSURE);
> +		if (val_p < 0)
> +			continue;
> +
> +		valid = true;
> +	}
> +
> +	input_report_abs(lradc->ts_input, ABS_PRESSURE, 0);
> +	input_report_key(lradc->ts_input, BTN_TOUCH, 0);
> +	input_sync(lradc->ts_input);
> +
> +	/* Do not restart the TS IRQ if the driver is shutting down. */
> +	if (lradc->stop_touchscreen)
> +		return;
> +
> +	/* Restart the touchscreen interrupts. */
> +	writel(LRADC_CTRL1_TOUCH_DETECT_IRQ,
> +		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);
> +	writel(LRADC_CTRL1_TOUCH_DETECT_IRQ_EN,
> +		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_SET);
> +}
> +
> +static int mxs_lradc_ts_open(struct input_dev *dev)
> +{
> +	struct mxs_lradc *lradc = input_get_drvdata(dev);
> +
> +	/* The touchscreen is starting. */
> +	lradc->stop_touchscreen = 0;
> +
> +	/* Enable the touch-detect circuitry. */
> +	writel(LRADC_CTRL0_TOUCH_DETECT_ENABLE,
> +		lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_SET);
> +
> +	/* Enable the touch-detect IRQ. */
> +	writel(LRADC_CTRL1_TOUCH_DETECT_IRQ_EN,
> +		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_SET);
> +
> +	return 0;
> +}
> +
> +static void mxs_lradc_ts_close(struct input_dev *dev)
> +{
> +	struct mxs_lradc *lradc = input_get_drvdata(dev);
> +
> +	/* Indicate the touchscreen is stopping. */
> +	lradc->stop_touchscreen = 1;
> +
> +	/* Disable touchscreen touch-detect IRQ. */
> +	writel(LRADC_CTRL1_TOUCH_DETECT_IRQ_EN,
> +		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);
> +
> +	/* Power-down touchscreen touch-detect circuitry. */
> +	writel(LRADC_CTRL0_TOUCH_DETECT_ENABLE,
> +		lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);
> +
> +	/* Wait until touchscreen thread finishes any possible remnants. */
> +	cancel_work_sync(&lradc->ts_work);
> +}
> +
> +static int mxs_lradc_ts_register(struct mxs_lradc *lradc)
> +{
> +	struct input_dev *input;
> +	struct device *dev = lradc->dev;
> +	int ret;
> +
> +	if (!lradc->use_touchscreen)
> +		return 0;
> +
> +	input = input_allocate_device();
> +	if (!input) {
> +		dev_warn(dev, "Failed to allocate TS device, disabling.\n");
> +		lradc->use_touchscreen = MXS_LRADC_TOUCHSCREEN_NONE;
> +		return 0;
> +	}
> +
> +	input->name = DRIVER_NAME;
> +	input->id.bustype = BUS_HOST;
> +	input->dev.parent = dev;
> +	input->open = mxs_lradc_ts_open;
> +	input->close = mxs_lradc_ts_close;
> +
> +	__set_bit(EV_ABS, input->evbit);
> +	__set_bit(EV_KEY, input->evbit);
> +	__set_bit(BTN_TOUCH, input->keybit);
> +	input_set_abs_params(input, ABS_X, 0, LRADC_CH_VALUE_MASK, 0, 0);
> +	input_set_abs_params(input, ABS_Y, 0, LRADC_CH_VALUE_MASK, 0, 0);
> +	input_set_abs_params(input, ABS_PRESSURE, 0, LRADC_CH_VALUE_MASK, 0, 0);
> +
> +	lradc->ts_input = input;
> +	input_set_drvdata(input, lradc);
> +	ret = input_register_device(input);
> +	if (ret)
> +		input_free_device(lradc->ts_input);
> +
> +	return ret;
> +}
> +
> +static void mxs_lradc_ts_unregister(struct mxs_lradc *lradc)
> +{
> +	if (!lradc->use_touchscreen)
> +		return;
> +
> +	if (!lradc->ts_input)
> +		return;
> +
> +	cancel_work_sync(&lradc->ts_work);
> +
> +	input_unregister_device(lradc->ts_input);
> +}
> +
> +/*
>   * IRQ Handling
>   */
>  static irqreturn_t mxs_lradc_handle_irq(int irq, void *data)
> @@ -202,14 +550,24 @@ static irqreturn_t mxs_lradc_handle_irq(int irq, void
> *data) struct iio_dev *iio = data;
>  	struct mxs_lradc *lradc = iio_priv(iio);
>  	unsigned long reg = readl(lradc->base + LRADC_CTRL1);
> +	const uint32_t ts_irq_mask =
> +		LRADC_CTRL1_TOUCH_DETECT_IRQ_EN |
> +		LRADC_CTRL1_TOUCH_DETECT_IRQ;
> 
>  	if (!(reg & LRADC_CTRL1_LRADC_IRQ_MASK))
>  		return IRQ_NONE;
> 
>  	/*
> -	 * Touchscreen IRQ handling code shall probably have priority
> -	 * and therefore shall be placed here.
> +	 * Touchscreen IRQ handling code has priority and therefore
> +	 * is placed here. In case touchscreen IRQ arrives, disable
> +	 * it ASAP
>  	 */
> +	if (reg & LRADC_CTRL1_TOUCH_DETECT_IRQ) {
> +		writel(ts_irq_mask,
> +			lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);
> +		if (!lradc->stop_touchscreen)
> +			schedule_work(&lradc->ts_work);
> +	}
> 
>  	if (iio_buffer_enabled(iio))
>  		iio_trigger_poll(iio->trig, iio_get_time_ns());
> @@ -306,8 +664,10 @@ static int mxs_lradc_buffer_preenable(struct iio_dev
> *iio) {
>  	struct mxs_lradc *lradc = iio_priv(iio);
>  	struct iio_buffer *buffer = iio->buffer;
> -	int ret = 0, chan, ofs = 0, enable = 0;
> -	uint32_t ctrl4 = 0;
> +	int ret = 0, chan, ofs = 0;
> +	unsigned long enable = 0;
> +	uint32_t ctrl4_set = 0;
> +	uint32_t ctrl4_clr = 0;
>  	uint32_t ctrl1_irq = 0;
>  	const uint32_t chan_value = LRADC_CH_ACCUMULATE |
>  		((LRADC_DELAY_TIMER_LOOP - 1) << LRADC_CH_NUM_SAMPLES_OFFSET);
> @@ -339,17 +699,20 @@ static int mxs_lradc_buffer_preenable(struct iio_dev
> *iio) writel(0xff, lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);
> 
>  	for_each_set_bit(chan, buffer->scan_mask, LRADC_MAX_TOTAL_CHANS) {
> -		ctrl4 |= chan << LRADC_CTRL4_LRADCSELECT_OFFSET(ofs);
> +		ctrl4_set |= chan << LRADC_CTRL4_LRADCSELECT_OFFSET(ofs);
> +		ctrl4_clr |= LRADC_CTRL4_LRADCSELECT_MASK(ofs);
>  		ctrl1_irq |= LRADC_CTRL1_LRADC_IRQ_EN(ofs);
>  		writel(chan_value, lradc->base + LRADC_CH(ofs));
> -		enable |= 1 << ofs;
> +		bitmap_set(&enable, ofs, 1);
>  		ofs++;
>  	};
> 
>  	writel(LRADC_DELAY_TRIGGER_LRADCS_MASK | LRADC_DELAY_KICK,
>  		lradc->base + LRADC_DELAY(0) + STMP_OFFSET_REG_CLR);
> 
> -	writel(ctrl4, lradc->base + LRADC_CTRL4);
> +	writel(ctrl4_clr, lradc->base + LRADC_CTRL4 + STMP_OFFSET_REG_CLR);
> +	writel(ctrl4_set, lradc->base + LRADC_CTRL4 + STMP_OFFSET_REG_SET);
> +
>  	writel(ctrl1_irq, lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_SET);
> 
>  	writel(enable << LRADC_DELAY_TRIGGER_LRADCS_OFFSET,
> @@ -384,9 +747,33 @@ static int mxs_lradc_buffer_postdisable(struct iio_dev
> *iio) static bool mxs_lradc_validate_scan_mask(struct iio_dev *iio,
>  					const unsigned long *mask)
>  {
> -	const int mw = bitmap_weight(mask, iio->masklength);
> -
> -	return mw <= LRADC_MAX_MAPPED_CHANS;
> +	struct mxs_lradc *lradc = iio_priv(iio);
> +	const int len = iio->masklength;
> +	const int map_chans = bitmap_weight(mask, len);
> +	int rsvd_chans = 0;
> +	unsigned long rsvd_mask = 0;
> +
> +	if (lradc->use_touchbutton)
> +		rsvd_mask |= CHAN_MASK_TOUCHBUTTON;
> +	if (lradc->use_touchscreen == MXS_LRADC_TOUCHSCREEN_4WIRE)
> +		rsvd_mask |= CHAN_MASK_TOUCHSCREEN_4WIRE;
> +	if (lradc->use_touchscreen == MXS_LRADC_TOUCHSCREEN_5WIRE)
> +		rsvd_mask |= CHAN_MASK_TOUCHSCREEN_5WIRE;
> +
> +	if (lradc->use_touchbutton)
> +		rsvd_chans++;
> +	if (lradc->use_touchscreen)
> +		rsvd_chans++;
> +
> +	/* Test for attempts to map channels with special mode of operation. */
> +	if (bitmap_intersects(mask, &rsvd_mask, len))
> +		return 0;
> +
> +	/* Test for attempts to map more channels then available slots. */
> +	if (map_chans + rsvd_chans > LRADC_MAX_MAPPED_CHANS)
> +		return 0;
> +
> +	return 1;
>  }
> 
>  static const struct iio_buffer_setup_ops mxs_lradc_buffer_ops = {
> @@ -435,15 +822,29 @@ static const struct iio_chan_spec
> mxs_lradc_chan_spec[] = {
> 
>  static void mxs_lradc_hw_init(struct mxs_lradc *lradc)
>  {
> -	int i;
> -	const uint32_t cfg =
> +	/* The ADC always uses DELAY CHANNEL 0. */
> +	const uint32_t adc_cfg =
> +		(1 << (LRADC_DELAY_TRIGGER_DELAYS_OFFSET + 0)) |
>  		(LRADC_DELAY_TIMER_PER << LRADC_DELAY_DELAY_OFFSET);
> 
>  	stmp_reset_block(lradc->base);
> 
> -	for (i = 0; i < LRADC_MAX_DELAY_CHANS; i++)
> -		writel(cfg | (1 << (LRADC_DELAY_TRIGGER_DELAYS_OFFSET + i)),
> -			lradc->base + LRADC_DELAY(i));
> +	/* Configure DELAY CHANNEL 0 for generic ADC sampling. */
> +	writel(adc_cfg, lradc->base + LRADC_DELAY(0));
> +
> +	/* Disable remaining DELAY CHANNELs */
> +	writel(0, lradc->base + LRADC_DELAY(1));
> +	writel(0, lradc->base + LRADC_DELAY(2));
> +	writel(0, lradc->base + LRADC_DELAY(3));
> +
> +	/* Configure the touchscreen type */
> +	writel(LRADC_CTRL0_TOUCH_SCREEN_TYPE,
> +		lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);
> +
> +	if (lradc->use_touchscreen == MXS_LRADC_TOUCHSCREEN_5WIRE) {
> +		writel(LRADC_CTRL0_TOUCH_SCREEN_TYPE,
> +			lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_SET);
> +	}
> 
>  	/* Start internal temperature sensing. */
>  	writel(0, lradc->base + LRADC_CTRL2);
> @@ -463,9 +864,11 @@ static void mxs_lradc_hw_stop(struct mxs_lradc *lradc)
>  static int __devinit mxs_lradc_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> +	struct device_node *node = dev->of_node;
>  	struct mxs_lradc *lradc;
>  	struct iio_dev *iio;
>  	struct resource *iores;
> +	uint32_t ts_wires = 0;
>  	int ret = 0;
>  	int i;
> 
> @@ -487,6 +890,21 @@ static int __devinit mxs_lradc_probe(struct
> platform_device *pdev) goto err_addr;
>  	}
> 
> +	INIT_WORK(&lradc->ts_work, mxs_lradc_ts_work);
> +
> +	/* Check if touchscreen is enabled in DT. */
> +	ret = of_property_read_u32(node, "fsl,lradc-touchscreen-wires",
> +				&ts_wires);
> +	if (ret)
> +		dev_info(dev, "Touchscreen not enabled.\n");
> +	else if (ts_wires == 4)
> +		lradc->use_touchscreen = MXS_LRADC_TOUCHSCREEN_4WIRE;
> +	else if (ts_wires == 5)
> +		lradc->use_touchscreen = MXS_LRADC_TOUCHSCREEN_5WIRE;
> +	else
> +		dev_warn(dev, "Unsupported number of touchscreen wires (%d)\n",
> +				ts_wires);
> +
>  	/* Grab all IRQ sources */
>  	for (i = 0; i < 13; i++) {
>  		lradc->irq[i] = platform_get_irq(pdev, i);
> @@ -524,11 +942,16 @@ static int __devinit mxs_lradc_probe(struct
> platform_device *pdev) if (ret)
>  		goto err_trig;
> 
> +	/* Register the touchscreen input device. */
> +	ret = mxs_lradc_ts_register(lradc);
> +	if (ret)
> +		goto err_dev;
> +
>  	/* Register IIO device. */
>  	ret = iio_device_register(iio);
>  	if (ret) {
>  		dev_err(dev, "Failed to register IIO device\n");
> -		goto err_dev;
> +		goto err_ts;
>  	}
> 
>  	/* Configure the hardware. */
> @@ -536,6 +959,8 @@ static int __devinit mxs_lradc_probe(struct
> platform_device *pdev)
> 
>  	return 0;
> 
> +err_ts:
> +	mxs_lradc_ts_unregister(lradc);
>  err_dev:
>  	mxs_lradc_trigger_remove(iio);
>  err_trig:
> @@ -550,6 +975,8 @@ static int __devexit mxs_lradc_remove(struct
> platform_device *pdev) struct iio_dev *iio = platform_get_drvdata(pdev);
>  	struct mxs_lradc *lradc = iio_priv(iio);
> 
> +	mxs_lradc_ts_unregister(lradc);
> +
>  	mxs_lradc_hw_stop(lradc);
> 
>  	iio_device_unregister(iio);