Input: ads7846 - optionally leave Vref on during differential measurements

On some LCDs leaving the Vref on provides much better readings.

Signed-off-by: Jarkko Oikarinen <jarkko.oikarinen@nokia.com>
Signed-off-by: Imre Deak <imre.deak@solidboot.com>
Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 03e527c16c23f54b2e6ed31d39e47b2b5ffb07d2..c34e59b720a68e6a976a7a25a434cff5d38493f9 100644 (file)
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -145,15 +145,16 @@ struct ads7846 {
 #define        MAX_12BIT       ((1<<12)-1)
 
 /* leave ADC powered up (disables penirq) between differential samples */
-#define        READ_12BIT_DFR(x) (ADS_START | ADS_A2A1A0_d_ ## x \
-       | ADS_12_BIT | ADS_DFR)
+#define        READ_12BIT_DFR(x, adc, vref) (ADS_START | ADS_A2A1A0_d_ ## x \
+       | ADS_12_BIT | ADS_DFR | \
+       (adc ? ADS_PD10_ADC_ON : 0) | (vref ? ADS_PD10_REF_ON : 0))
 
-#define        READ_Y  (READ_12BIT_DFR(y)  | ADS_PD10_ADC_ON)
-#define        READ_Z1 (READ_12BIT_DFR(z1) | ADS_PD10_ADC_ON)
-#define        READ_Z2 (READ_12BIT_DFR(z2) | ADS_PD10_ADC_ON)
+#define        READ_Y(vref)    (READ_12BIT_DFR(y,  1, vref))
+#define        READ_Z1(vref)   (READ_12BIT_DFR(z1, 1, vref))
+#define        READ_Z2(vref)   (READ_12BIT_DFR(z2, 1, vref))
 
-#define        READ_X  (READ_12BIT_DFR(x)  | ADS_PD10_ADC_ON)
-#define        PWRDOWN (READ_12BIT_DFR(y)  | ADS_PD10_PDOWN)   /* LAST */
+#define        READ_X(vref)    (READ_12BIT_DFR(x,  1, vref))
+#define        PWRDOWN         (READ_12BIT_DFR(y,  0, 0))      /* LAST */
 
 /* single-ended samples need to first power up reference voltage;
  * we leave both ADC and VREF powered
@@ -161,8 +162,8 @@ struct ads7846 {
 #define        READ_12BIT_SER(x) (ADS_START | ADS_A2A1A0_ ## x \
        | ADS_12_BIT | ADS_SER)
 
-#define        REF_ON  (READ_12BIT_DFR(x) | ADS_PD10_ALL_ON)
-#define        REF_OFF (READ_12BIT_DFR(y) | ADS_PD10_PDOWN)
+#define        REF_ON  (READ_12BIT_DFR(x, 1, 1))
+#define        REF_OFF (READ_12BIT_DFR(y, 0, 0))
 
 /*--------------------------------------------------------------------------*/
 
@@ -670,6 +671,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
        struct ads7846_platform_data    *pdata = spi->dev.platform_data;
        struct spi_message              *m;
        struct spi_transfer             *x;
+       int                             vref;
        int                             err;
 
        if (!spi->irq) {
@@ -767,6 +769,8 @@ static int __devinit ads7846_probe(struct spi_device *spi)
        input_set_abs_params(input_dev, ABS_PRESSURE,
                        pdata->pressure_min, pdata->pressure_max, 0, 0);
 
+       vref = pdata->keep_vref_on;
+
        /* set up the transfers to read touchscreen state; this assumes we
         * use formula #2 for pressure, not #3.
         */
@@ -776,7 +780,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
        spi_message_init(m);
 
        /* y- still on; turn on only y+ (and ADC) */
-       ts->read_y = READ_Y;
+       ts->read_y = READ_Y(vref);
        x->tx_buf = &ts->read_y;
        x->len = 1;
        spi_message_add_tail(x, m);
@@ -794,7 +798,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 
        /* turn y- off, x+ on, then leave in lowpower */
        x++;
-       ts->read_x = READ_X;
+       ts->read_x = READ_X(vref);
        x->tx_buf = &ts->read_x;
        x->len = 1;
        spi_message_add_tail(x, m);
@@ -813,7 +817,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
                spi_message_init(m);
 
                x++;
-               ts->read_z1 = READ_Z1;
+               ts->read_z1 = READ_Z1(vref);
                x->tx_buf = &ts->read_z1;
                x->len = 1;
                spi_message_add_tail(x, m);
@@ -830,7 +834,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
                spi_message_init(m);
 
                x++;
-               ts->read_z2 = READ_Z2;
+               ts->read_z2 = READ_Z2(vref);
                x->tx_buf = &ts->read_z2;
                x->len = 1;
                spi_message_add_tail(x, m);

diff --git a/include/linux/spi/ads7846.h b/include/linux/spi/ads7846.h
index 1663f940ca115d3a5a2455203fe1df0d200229a9..3387e44dfd13bdef5014e050aff8e85637387048 100644 (file)
--- a/include/linux/spi/ads7846.h
+++ b/include/linux/spi/ads7846.h
@@ -14,6 +14,8 @@ enum ads7846_filter {
 struct ads7846_platform_data {
        u16     model;                  /* 7843, 7845, 7846. */
        u16     vref_delay_usecs;       /* 0 for external vref; etc */
+       int     keep_vref_on:1;         /* set to keep vref on for differential
+                                        * measurements as well */
        u16     x_plate_ohms;
        u16     y_plate_ohms;