iio: adc: at91: Add support for Touchscreen Switches Closure Time

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@atmel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
index 52430ba..0331c7a 100644 (file)
--- 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;