xref: /OK3568_Linux_fs/kernel/Documentation/devicetree/bindings/input/touchscreen/ti-tsc-adc.txt (revision 4882a59341e53eb6f0b4789bf948001014eff981)

* TI - TSC ADC (Touschscreen and analog digital converter)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Required properties:
- mfd
	compatible: Should be
		"ti,am3359-tscadc" for AM335x/AM437x SoCs
		"ti,am654-tscadc", "ti,am3359-tscadc" for AM654 SoCs
- child "tsc"
	compatible: Should be "ti,am3359-tsc".
	ti,wires: Wires refer to application modes i.e. 4/5/8 wire touchscreen
		  support on the platform.
	ti,x-plate-resistance: X plate resistance
	ti,coordinate-readouts: The sequencer supports a total of 16
				programmable steps each step is used to
				read a single coordinate. A single
                                readout is enough but multiple reads can
				increase the quality.
				A value of 5 means, 5 reads for X, 5 for
				Y and 2 for Z (always). This utilises 12
				of the 16 software steps available. The
				remaining 4 can be used by the ADC.
	ti,wire-config: Different boards could have a different order for
			connecting wires on touchscreen. We need to provide an
			8 bit number where in the 1st four bits represent the
			analog lines and the next 4 bits represent positive/
			negative terminal on that input line. Notations to
			represent the input lines and terminals resoectively
			is as follows:
			AIN0 = 0, AIN1 = 1 and so on till AIN7 = 7.
			XP  = 0, XN = 1, YP = 2, YN = 3.
- child "adc"
	compatible: Should be
		    "ti,am3359-adc" for AM335x/AM437x SoCs
		    "ti,am654-adc", "ti,am3359-adc" for AM654 SoCs
	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".

- child "adc"
	ti,chan-step-opendelay: List of open delays for each channel of
				ADC in the order of ti,adc-channels. The
				value corresponds to the number of ADC
				clock cycles to wait after applying the
				step configuration registers and before
				sending the start of ADC conversion.
				Maximum value is 0x3FFFF.
       ti,chan-step-sampledelay: List of sample delays for each channel
				  of ADC in the order of ti,adc-channels.
				  The value corresponds to the number of
				  ADC clock cycles to sample (to hold
				  start of conversion high).
				  Maximum value is 0xFF.
       ti,chan-step-avg: Number of averages to be performed for each
			  channel of ADC. If average is 16 then input
			  is sampled 16 times and averaged to get more
			  accurate value. This increases the time taken
			  by ADC to generate a sample. Valid range is 0
			  average to 16 averages. Maximum value is 16.

Example:
	tscadc: tscadc@44e0d000 {
		compatible = "ti,am3359-tscadc";
		tsc {
			ti,wires = <4>;
			ti,x-plate-resistance = <200>;
			ti,coordiante-readouts = <5>;
			ti,wire-config = <0x00 0x11 0x22 0x33>;
			ti,charge-delay = <0x400>;
		};

		adc {
			ti,adc-channels = <4 5 6 7>;
			ti,chan-step-opendelay = <0x098 0x3ffff 0x098 0x0>;
			ti,chan-step-sampledelay = <0xff 0x0 0xf 0x0>;
			ti,chan-step-avg = <16 2 4 8>;
		};
	}