Input: sun4i-ts - allow controlling filter and sensitivity via DT

This commit introduces two new optional device-tree properties:
"tp-sensitive-adjust": adjust sensitivity of pen down detection
"filter-type": select median and averaging filter

The previous fixed defaults, didn't work well for the Olimex
A13-LCD10TS (I have).

Signed-off-by: Jens Thiele <[e-mail]>
Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

Documentation/devicetree/bindings/input/touchscreen/sun4i.txt

···
  - #thermal-sensor-cells: shall be 0
 
 Optional properties:
- - allwinner,ts-attached: boolean indicating that an actual touchscreen is
-			  attached to the controller
+ - allwinner,ts-attached	 : boolean indicating that an actual touchscreen
+				   is attached to the controller
+ - allwinner,tp-sensitive-adjust : integer (4 bits)
+				   adjust sensitivity of pen down detection
+				   between 0 (least sensitive) and 15
+				   (defaults to 15)
+ - allwinner,filter-type	 : integer (2 bits)
+				   select median and averaging filter
+				   samples used for median / averaging filter
+				   0: 4/2
+				   1: 5/3
+				   2: 8/4
+				   3: 16/8
+				   (defaults to 1)
 
 Example:
 
···
 		interrupts = <29>;
 		allwinner,ts-attached;
 		#thermal-sensor-cells = <0>;
+		/* sensitive/noisy touch panel */
+		allwinner,tp-sensitive-adjust = <0>;
+		allwinner,filter-type = <3>;
 	};

drivers/input/touchscreen/sun4i-ts.c

···
  * These kinds of heuristics are just asking for trouble (and don't belong
  * in the kernel). So this driver offers straight forward, reliable single
  * touch functionality only.
+ *
+ * s.a. A20 User Manual "1.15 TP" (Documentation/arm/sunxi/README)
+ * (looks like the description in the A20 User Manual v1.3 is better
+ * than the one in the A10 User Manual v.1.5)
  */
 
 #include <linux/err.h>
···
 	int error;
 	u32 reg;
 	bool ts_attached;
+	u32 tp_sensitive_adjust = 15;
+	u32 filter_type = 1;
 
 	ts = devm_kzalloc(dev, sizeof(struct sun4i_ts_data), GFP_KERNEL);
 	if (!ts)
···
 	       ts->base + TP_CTRL0);
 
 	/*
-	 * sensitive_adjust = 15 : max, which is not all that sensitive,
+	 * tp_sensitive_adjust is an optional property
 	 * tp_mode = 0 : only x and y coordinates, as we don't use dual touch
 	 */
-	writel(TP_SENSITIVE_ADJUST(15) | TP_MODE_SELECT(0),
+	of_property_read_u32(np, "allwinner,tp-sensitive-adjust",
+			     &tp_sensitive_adjust);
+	writel(TP_SENSITIVE_ADJUST(tp_sensitive_adjust) | TP_MODE_SELECT(0),
 	       ts->base + TP_CTRL2);
 
-	/* Enable median filter, type 1 : 5/3 */
-	writel(FILTER_EN(1) | FILTER_TYPE(1), ts->base + TP_CTRL3);
+	/*
+	 * Enable median and averaging filter, optional property for
+	 * filter type.
+	 */
+	of_property_read_u32(np, "allwinner,filter-type", &filter_type);
+	writel(FILTER_EN(1) | FILTER_TYPE(filter_type), ts->base + TP_CTRL3);
 
 	/* Enable temperature measurement, period 1953 (2 seconds) */
 	writel(TEMP_ENABLE(1) | TEMP_PERIOD(1953), ts->base + TP_TPR);