[PATCH v5 8/8] Input: resistive-adc-touch: add support for z1 and z2 channels

Oleksij Rempel
2021-05-21T04:46:14Z

This patch adds support for the z1 and z2 channels. These are used to
calculate the applied pressure. As there is no common order of the
individual channels of a resistive touch ADC, support for
io-channel-names is added (although the DT bindings stated the
driver already supports these).

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
.../input/touchscreen/resistive-adc-touch.c | 142 ++++++++++++++++--
1 file changed, 128 insertions(+), 14 deletions(-)

diff --git a/drivers/input/touchscreen/resistive-adc-touch.c b/drivers/input/touchscreen/resistive-adc-touch.c
index e50af30183f4..fa90005b7bc9 100644
--- a/drivers/input/touchscreen/resistive-adc-touch.c
+++ b/drivers/input/touchscreen/resistive-adc-touch.c
@@ -20,7 +20,18 @@

#define DRIVER_NAME "resistive-adc-touch"
#define GRTS_DEFAULT_PRESSURE_MIN 50000
+#define GRTS_DEFAULT_PRESSURE_MAX 65535
#define GRTS_MAX_POS_MASK GENMASK(11, 0)
+#define GRTS_MAX_CHANNELS 4
+
+enum grts_ch_type {
+ GRTS_CH_NONE = 0,
+ GRTS_CH_X,
+ GRTS_CH_Y,
+ GRTS_CH_PRESSURE,
+ GRTS_CH_Z1,
+ GRTS_CH_Z2,
+};

/**
* struct grts_state - generic resistive touch screen information struct
@@ -33,24 +44,61 @@
*/
struct grts_state {
u32 pressure_min;
+ u32 x_plate_ohms;
bool pressure;
struct iio_channel *iio_chans;
struct iio_cb_buffer *iio_cb;
struct input_dev *input;
struct touchscreen_properties prop;
+ u8 ch[GRTS_MAX_CHANNELS];
};

static int grts_cb(const void *data, void *private)
{
const u16 *touch_info = data;
struct grts_state *st = private;
- unsigned int x, y, press = 0x0;
+ unsigned int x, y, press = 0, z1 = 0, z2;
+ unsigned int Rt, i;
+
+ for (i = 0; i < ARRAY_SIZE(st->ch) && st->ch[i] != GRTS_CH_NONE; i++) {
+ switch (st->ch[i]) {
+ case GRTS_CH_X:
+ x = touch_info[i];
+ break;
+ case GRTS_CH_Y:
+ y = touch_info[i];
+ break;
+ case GRTS_CH_PRESSURE:
+ press = touch_info[i];
+ break;
+ case GRTS_CH_Z1:
+ z1 = touch_info[i];
+ break;
+ case GRTS_CH_Z2:
+ z2 = touch_info[i];
+ break;
+ case GRTS_CH_NONE:
+ break;
+ }
+ }

- /* channel data coming in buffer in the order below */
- x = touch_info[0];
- y = touch_info[1];
- if (st->pressure)
- press = touch_info[2];
+ if (z1) {
+ Rt = z2;
+ Rt -= z1;
+ Rt *= st->x_plate_ohms;
+ Rt = DIV_ROUND_CLOSEST(Rt, 16);
+ Rt *= x;
+ Rt /= z1;
+ Rt = DIV_ROUND_CLOSEST(Rt, 256);
+ /*
+ * On increased pressure the resistance (Rt) is decreasing
+ * so, convert values to make it looks as real pressure.
+ */
+ if (Rt < GRTS_DEFAULT_PRESSURE_MAX)
+ press = GRTS_DEFAULT_PRESSURE_MAX - Rt;
+ else
+ press = 0;
+ }

if ((!x && !y) || (st->pressure && (press < st->pressure_min))) {
/* report end of touch */
@@ -94,12 +142,77 @@ static void grts_disable(void *data)
iio_channel_release_all_cb(data);
}

+static int grts_get_properties(struct grts_state *st, struct device *dev)
+{
+ int idx, error;
+
+ idx = device_property_match_string(dev, "io-channel-names", "x");
+ if (idx < 0)
+ return idx;
+
+ if (idx >= ARRAY_SIZE(st->ch))
+ return -EOVERFLOW;
+
+ st->ch[idx] = GRTS_CH_X;
+
+ idx = device_property_match_string(dev, "io-channel-names", "y");
+ if (idx < 0)
+ return idx;
+
+ if (idx >= ARRAY_SIZE(st->ch))
+ return -EOVERFLOW;
+
+ st->ch[idx] = GRTS_CH_Y;
+
+ /* pressure is optional */
+ idx = device_property_match_string(dev, "io-channel-names", "pressure");
+ if (idx >= 0) {
+ if (idx >= ARRAY_SIZE(st->ch))
+ return -EOVERFLOW;
+
+ st->ch[idx] = GRTS_CH_PRESSURE;
+ st->pressure = true;
+
+ return 0;
+ }
+
+ /* if no pressure is defined, try optional z1 + z2 */
+ idx = device_property_match_string(dev, "io-channel-names", "z1");
+ if (idx < 0)
+ return 0;
+
+ if (idx >= ARRAY_SIZE(st->ch))
+ return -EOVERFLOW;
+
+ st->ch[idx] = GRTS_CH_Z1;
+
+ /* if z1 is provided z2 is not optional */
+ idx = device_property_match_string(dev, "io-channel-names", "z2");
+ if (idx < 0)
+ return idx;
+
+ if (idx >= ARRAY_SIZE(st->ch))
+ return -EOVERFLOW;
+
+ st->ch[idx] = GRTS_CH_Z2;
+ st->pressure = true;
+
+ error = device_property_read_u32(dev,
+ "touchscreen-x-plate-ohms",
+ &st->x_plate_ohms);
+ if (error) {
+ dev_err(dev, "can't get touchscreen-x-plate-ohms property\n");
+ return error;
+ }
+
+ return 0;
+}
+
static int grts_probe(struct platform_device *pdev)
{
struct grts_state *st;
struct input_dev *input;
struct device *dev = &pdev->dev;
- struct iio_channel *chan;
int error;

st = devm_kzalloc(dev, sizeof(struct grts_state), GFP_KERNEL);
@@ -115,12 +228,13 @@ static int grts_probe(struct platform_device *pdev)
return error;
}

- chan = &st->iio_chans[0];
- st->pressure = false;
- while (chan && chan->indio_dev) {
- if (!strcmp(chan->channel->datasheet_name, "pressure"))
- st->pressure = true;
- chan++;
+ if (!device_property_present(dev, "io-channel-names"))
+ return -ENODEV;
+
+ error = grts_get_properties(st, dev);
+ if (error) {
+ dev_err(dev, "Failed to parse properties\n");
+ return error;
}

if (st->pressure) {
@@ -148,7 +262,7 @@ static int grts_probe(struct platform_device *pdev)
input_set_abs_params(input, ABS_Y, 0, GRTS_MAX_POS_MASK - 1, 0, 0);
if (st->pressure)
input_set_abs_params(input, ABS_PRESSURE, st->pressure_min,
- 0xffff, 0, 0);
+ GRTS_DEFAULT_PRESSURE_MAX, 0, 0);

input_set_capability(input, EV_KEY, BTN_TOUCH);

--
2.29.2