Input: ti_am335x_tsc - read charge delay from DT

This patch reads charge delay from tsc DT node and writes to
REG_CHARGEDELAY register. If the charge delay is not specified in DT then
default value of 0x400(CHARGEDLY_OPENDLY) is used.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

2 files changed, 28 insertions, 1 deletions

diff --git a/Documentation/devicetree/bindings/input/touchscreen/ti-tsc-adc.txt b/Documentation/devicetree/bindings/input/touchscreen/ti-tsc-adc.txt
index 878549ba814d..6c4fb34823d3 100644
--- a/Documentation/devicetree/bindings/input/touchscreen/ti-tsc-adc.txt
+++ b/Documentation/devicetree/bindings/input/touchscreen/ti-tsc-adc.txt
@@ -28,6 +28,20 @@ Required properties:
         ti,adc-channels: List of analog inputs available for ADC.
                          AIN0 = 0, AIN1 = 1 and so on till AIN7 = 7.
 
+Optional properties:
+- child "tsc"
+        ti,charge-delay: Length of touch screen charge delay step in terms of
+                         ADC clock cycles. Charge delay value should be large
+                         in order to avoid false pen-up events. This value
+                         effects the overall sampling speed, hence need to be
+                         kept as low as possible, while avoiding false pen-up
+                         event. Start from a lower value, say 0x400, and
+                         increase value until false pen-up events are avoided.
+                         The pen-up detection happens immediately after the
+                         charge step, so this does in fact function as a
+                         hardware knob for adjusting the amount of "settling
+                         time".
+
 Example:
         tscadc: tscadc@44e0d000 {
                 compatible = "ti,am3359-tscadc";
@@ -36,6 +50,7 @@ Example:
                         ti,x-plate-resistance = <200>;
                         ti,coordiante-readouts = <5>;
                         ti,wire-config = <0x00 0x11 0x22 0x33>;
+                        ti,charge-delay = <0x400>;
                 };
 
                 adc {
diff --git a/drivers/input/touchscreen/ti_am335x_tsc.c b/drivers/input/touchscreen/ti_am335x_tsc.c
index 0625c102a1d0..7c0f6b21559d 100644
--- a/drivers/input/touchscreen/ti_am335x_tsc.c
+++ b/drivers/input/touchscreen/ti_am335x_tsc.c
@@ -52,6 +52,7 @@ struct titsc {
         u32                     bit_xp, bit_xn, bit_yp, bit_yn;
         u32                     inp_xp, inp_xn, inp_yp, inp_yn;
         u32                     step_mask;
+        u32                     charge_delay;
 };
 
 static unsigned int titsc_readl(struct titsc *ts, unsigned int reg)
@@ -177,7 +178,7 @@ static void titsc_step_config(struct titsc *ts_dev)
 
         config = titsc_readl(ts_dev, REG_IDLECONFIG);
         titsc_writel(ts_dev, REG_CHARGECONFIG, config);
-        titsc_writel(ts_dev, REG_CHARGEDELAY, CHARGEDLY_OPENDLY);
+        titsc_writel(ts_dev, REG_CHARGEDELAY, ts_dev->charge_delay);
 
         /* coordinate_readouts + 1 ... coordinate_readouts + 2 is for Z */
         config = STEPCONFIG_MODE_HWSYNC |
@@ -368,6 +369,17 @@ static int titsc_parse_dt(struct platform_device *pdev,
         if (err < 0)
                 return err;
 
+        err = of_property_read_u32(node, "ti,charge-delay",
+                                   &ts_dev->charge_delay);
+        /*
+         * If ti,charge-delay value is not specified, then use
+         * CHARGEDLY_OPENDLY as the default value.
+         */
+        if (err < 0) {
+                ts_dev->charge_delay = CHARGEDLY_OPENDLY;
+                dev_warn(&pdev->dev, "ti,charge-delay not specified\n");
+        }
+
         return of_property_read_u32_array(node, "ti,wire-config",
                         ts_dev->config_inp, ARRAY_SIZE(ts_dev->config_inp));
 }