[PATCH v3 4/6] ARM: dts: AM335x: Make charge delay a DT parameter for tsc

Vignesh R
2014-11-11T08:34:02Z

The charge delay value is by default 0xB000. But it can be set to lower
values on some boards as long as false pen-ups are avoided. Lowering the
value increases the sampling rate (though current sampling rate is
sufficient for tsc operation). Hence charge delay has been made a DT
parameter.

Signed-off-by: Vignesh R <vigneshr@ti.com>
---
.../devicetree/bindings/input/touchscreen/ti-tsc-adc.txt | 15 +++++++++++++++
arch/arm/boot/dts/am335x-evm.dts | 1 +
2 files changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/input/touchscreen/ti-tsc-adc.txt b/Documentation/devicetree/bindings/input/touchscreen/ti-tsc-adc.txt
index 878549ba814d..b87574bae009 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
+ affects 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 = <0xB000>;
};

adc {
diff --git a/arch/arm/boot/dts/am335x-evm.dts b/arch/arm/boot/dts/am335x-evm.dts
index e2156a583de7..80be0462298b 100644
--- a/arch/arm/boot/dts/am335x-evm.dts
+++ b/arch/arm/boot/dts/am335x-evm.dts
@@ -641,6 +641,7 @@
ti,x-plate-resistance = <200>;
ti,coordinate-readouts = <5>;
ti,wire-config = <0x00 0x11 0x22 0x33>;
+ ti,charge-delay = <0xB000>;
};

adc {
--
1.9.1