linux-kernel - Re: [PATCH] iio: adc: at91: Add support for Touchscreen Switches Closure Time

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Date:   Sat, 3 Sep 2016 17:24:43 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Nicolas Ferre <nicolas.ferre@...el.com>,
        Cristian Birsan <cristian.birsan@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...el.com>
Cc:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org
Subject: Re: [PATCH] iio: adc: at91: Add support for Touchscreen Switches
 Closure Time

On 30/08/16 13:27, Nicolas Ferre wrote:
> On newer components compatible with the at91sam9x5, the Touchscreen
> Switches Closure Time or TSSCTIM value of the Touchscreen Mode Register is
> not filled at all.
> On some hardware, having no time indicated for it may lead to incoherent
> values and jitter.
> We fix this time to 10us as it is usually difficult to retrieve impedance
> values from LCD manufacturers.
> 
> Signed-off-by: Nicolas Ferre <nicolas.ferre@...el.com>
Hi Nicolas,

Stable / fixes material or just have it head for the next merge window?


Jonathan
> ---
>  drivers/iio/adc/at91_adc.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
> index 0438c68015e8..bbdac07f4aaa 100644
> --- a/drivers/iio/adc/at91_adc.c
> +++ b/drivers/iio/adc/at91_adc.c
> @@ -113,6 +113,7 @@
>  #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_SCTIM_(x)		((x) << 16)
>  #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 */
> @@ -150,6 +151,7 @@
>  #define MAX_RLPOS_BITS         10
>  #define TOUCH_SAMPLE_PERIOD_US_RL      10000   /* 10ms, the SoC can't keep up with 2ms */
>  #define TOUCH_SHTIM                    0xa
> +#define TOUCH_SCTIM_US		10		/* 10us for the Touchscreen Switches Closure Time */
>  
>  /**
>   * struct at91_adc_reg_desc - Various informations relative to registers
> @@ -1001,7 +1003,9 @@ static void atmel_ts_close(struct input_dev *dev)
>  
>  static int at91_ts_hw_init(struct at91_adc_state *st, u32 adc_clk_khz)
>  {
> +	struct iio_dev *idev = iio_priv_to_dev(st);
>  	u32 reg = 0;
> +	u32 tssctim = 0;
>  	int i = 0;
>  
>  	/* a Pen Detect Debounce Time is necessary for the ADC Touch to avoid
> @@ -1034,11 +1038,20 @@ static int at91_ts_hw_init(struct at91_adc_state *st, u32 adc_clk_khz)
>  		return 0;
>  	}
>  
> +	/* Touchscreen Switches Closure time needed for allowing the value to
> +	 * stabilize.
> +	 * Switch Closure Time = (TSSCTIM * 4) ADCClock periods
> +	 */
> +	tssctim = DIV_ROUND_UP(TOUCH_SCTIM_US * adc_clk_khz / 1000, 4);
> +	dev_dbg(&idev->dev, "adc_clk at: %d KHz, tssctim at: %d\n",
> +		adc_clk_khz, tssctim);
> +
>  	if (st->touchscreen_type == ATMEL_ADC_TOUCHSCREEN_4WIRE)
>  		reg = AT91_ADC_TSMR_TSMODE_4WIRE_PRESS;
>  	else
>  		reg = AT91_ADC_TSMR_TSMODE_5WIRE;
>  
> +	reg |= AT91_ADC_TSMR_SCTIM_(tssctim) & AT91_ADC_TSMR_SCTIM;
>  	reg |= AT91_ADC_TSMR_TSAV_(st->caps->ts_filter_average)
>  	       & AT91_ADC_TSMR_TSAV;
>  	reg |= AT91_ADC_TSMR_PENDBC_(st->ts_pendbc) & AT91_ADC_TSMR_PENDBC;
>