[PATCH v5 4/6] ARM: dts: AM335x: Make charge delay a DT parameter for TSC

[Tony Lindgren]

* Vignesh R <vigneshr at ti.com> [141223 23:07]:
> The charge delay value is by default 0x400. 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). In some boards, the value has to be
> increased to avoid false pen-up events. Hence, charge delay has been
> made a DT parameter.
> 
> Signed-off-by: Vignesh R <vigneshr at ti.com>

Assuming this binding makes sense for the input people, there should
be no conflicts merging this patch along with the rest of the series
via the input tree.

Sounds like this value probably depends on the size of the touchscreen
for the capacitance, so a numeric value is really needed here. Of course
I would personally prefer generic bindings in general, but in any case
please feel free to merge along with the other input patches:

Acked-by: Tony Lindgren <tony at atomide.com>


> ---
> v4:
>  - Set charge delay to 0x400 as default. Most devices function normally
>    at this value
> 
>  .../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..6df5028a4ad3 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 at 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/arch/arm/boot/dts/am335x-evm.dts b/arch/arm/boot/dts/am335x-evm.dts
> index 54f118c08db8..66342515df20 100644
> --- a/arch/arm/boot/dts/am335x-evm.dts
> +++ b/arch/arm/boot/dts/am335x-evm.dts
> @@ -648,6 +648,7 @@
>  		ti,x-plate-resistance = <200>;
>  		ti,coordinate-readouts = <5>;
>  		ti,wire-config = <0x00 0x11 0x22 0x33>;
> +		ti,charge-delay = <0x400>;
>  	};
>  
>  	adc {
> -- 
> 1.9.1
>