iio: at91: introduce touch screen support in iio adc driver

AT91 ADC hardware integrate touch screen support. So this patch add touch
screen support for at91 adc iio driver.
To enable touch screen support in adc, you need to add the dt parameters:
  1. which type of touch are used? (4 or 5 wires), sample period time.
  2. correct pressure detect threshold value.

In the meantime, since touch screen will use a interal period trigger of adc,
so it is conflict to other hardware triggers. Driver will disable the hardware
trigger support if touch screen is enabled.

This driver has been tested in AT91SAM9X5-EK and SAMA5D3x-EK.
Signed-off-by: Josh Wu <josh.wu@atmel.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
CC: devicetree@vger.kernel.org
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/arm/atmel-adc.txt

@@ -23,6 +23,13 @@ Optional properties:
 		       resolution will be used.
   - atmel,adc-sleep-mode: Boolean to enable sleep mode when no conversion
   - atmel,adc-sample-hold-time: Sample and Hold Time in microseconds
+  - atmel,adc-ts-wires: Number of touch screen wires. Should be 4 or 5. If this
+                        value is set, then adc driver will enable touch screen
+                        support.
+    NOTE: when adc touch screen enabled, the adc hardware trigger will be
+          disabled. Since touch screen will occupied the trigger register.
+  - atmel,adc-ts-pressure-threshold: a pressure threshold for touchscreen. It
+                                     make touch detect more precision.
  
 Optional trigger Nodes:
   - Required properties:

arch/arm/mach-at91/include/mach/at91_adc.h

@@ -60,14 +60,48 @@
 #define AT91_ADC_IER		0x24		/* Interrupt Enable Register */
 #define AT91_ADC_IDR		0x28		/* Interrupt Disable Register */
 #define AT91_ADC_IMR		0x2C		/* Interrupt Mask Register */
+#define		AT91_ADC_IER_PEN	(1 << 29)
+#define		AT91_ADC_IER_NOPEN	(1 << 30)
+#define		AT91_ADC_IER_XRDY	(1 << 20)
+#define		AT91_ADC_IER_YRDY	(1 << 21)
+#define		AT91_ADC_IER_PRDY	(1 << 22)
+#define		AT91_ADC_ISR_PENS	(1 << 31)
 
 #define AT91_ADC_CHR(n)		(0x30 + ((n) * 4))	/* Channel Data Register N */
 #define		AT91_ADC_DATA		(0x3ff)
 
 #define AT91_ADC_CDR0_9X5	(0x50)			/* Channel Data Register 0 for 9X5 */
 
+#define AT91_ADC_ACR		0x94	/* Analog Control Register */
+#define		AT91_ADC_ACR_PENDETSENS	(0x3 << 0)	/* pull-up resistor */
+
+#define AT91_ADC_TSMR		0xB0
+#define		AT91_ADC_TSMR_TSMODE	(3 << 0)	/* Touch Screen Mode */
+#define			AT91_ADC_TSMR_TSMODE_NONE		(0 << 0)
+#define			AT91_ADC_TSMR_TSMODE_4WIRE_NO_PRESS	(1 << 0)
+#define			AT91_ADC_TSMR_TSMODE_4WIRE_PRESS	(2 << 0)
+#define			AT91_ADC_TSMR_TSMODE_5WIRE		(3 << 0)
+#define		AT91_ADC_TSMR_TSAV	(3 << 4)	/* Averages samples */
+#define			AT91_ADC_TSMR_TSAV_(x)		((x) << 4)
+#define		AT91_ADC_TSMR_SCTIM	(0x0f << 16)	/* Switch closure time */
+#define		AT91_ADC_TSMR_PENDBC	(0x0f << 28)	/* Pen Debounce time */
+#define			AT91_ADC_TSMR_PENDBC_(x)	((x) << 28)
+#define		AT91_ADC_TSMR_NOTSDMA	(1 << 22)	/* No Touchscreen DMA */
+#define		AT91_ADC_TSMR_PENDET_DIS	(0 << 24)	/* Pen contact detection disable */
+#define		AT91_ADC_TSMR_PENDET_ENA	(1 << 24)	/* Pen contact detection enable */
+
+#define AT91_ADC_TSXPOSR	0xB4
+#define AT91_ADC_TSYPOSR	0xB8
+#define AT91_ADC_TSPRESSR	0xBC
+
 #define AT91_ADC_TRGR_9260	AT91_ADC_MR
 #define AT91_ADC_TRGR_9G45	0x08
 #define AT91_ADC_TRGR_9X5	0xC0
 
+/* Trigger Register bit field */
+#define		AT91_ADC_TRGR_TRGPER	(0xffff << 16)
+#define			AT91_ADC_TRGR_TRGPER_(x)	((x) << 16)
+#define		AT91_ADC_TRGR_TRGMOD	(0x7 << 0)
+#define			AT91_ADC_TRGR_MOD_PERIOD_TRIG	(5 << 0)
+
 #endif