2 files changed, 15 insertions, 1 deletions

diff --git a/Documentation/devicetree/bindings/arm/atmel-adc.txt b/Documentation/devicetree/bindings/arm/atmel-adc.txt
index 3a05492acdaf..16769d9cedd6 100644
--- a/Documentation/devicetree/bindings/arm/atmel-adc.txt
+++ b/Documentation/devicetree/bindings/arm/atmel-adc.txt
@@ -26,6 +26,7 @@ Optional properties:
                        atmel,adc-res-names property. If not specified, the highest
                        resolution will be used.
   - atmel,adc-sleep-mode: Boolean to enable sleep mode when no conversion
+  - atmel,adc-sample-hold-time: Sample and Hold Time in microseconds
  
 Optional trigger Nodes:
   - Required properties:
diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
index 7295bc5280bd..e5b88d5d3b59 100644
--- a/drivers/iio/adc/at91_adc.c
+++ b/drivers/iio/adc/at91_adc.c
@@ -52,6 +52,7 @@ struct at91_adc_state {
         void __iomem            *reg_base;
         struct at91_adc_reg_desc *registers;
         u8                      startup_time;
+        u8                      sample_hold_time;
         bool                    sleep_mode;
         struct iio_trigger      **trig;
         struct at91_adc_trigger *trigger_list;
@@ -465,6 +466,9 @@ static int at91_adc_probe_dt(struct at91_adc_state *st,
         }
         st->startup_time = prop;
 
+        prop = 0;
+        of_property_read_u32(node, "atmel,adc-sample-hold-time", &prop);
+        st->sample_hold_time = prop;
 
         if (of_property_read_u32(node, "atmel,adc-vref", &prop)) {
                 dev_err(&idev->dev, "Missing adc-vref property in the DT.\n");
@@ -578,7 +582,7 @@ static const struct iio_info at91_adc_info = {
 
 static int at91_adc_probe(struct platform_device *pdev)
 {
-        unsigned int prsc, mstrclk, ticks, adc_clk;
+        unsigned int prsc, mstrclk, ticks, adc_clk, shtim;
         int ret;
         struct iio_dev *idev;
         struct at91_adc_state *st;
@@ -691,12 +695,21 @@ static int at91_adc_probe(struct platform_device *pdev)
          */
         ticks = round_up((st->startup_time * adc_clk /
                           1000000) - 1, 8) / 8;
+        /*
+         * a minimal Sample and Hold Time is necessary for the ADC to guarantee
+         * the best converted final value between two channels selection
+         * The formula thus is : Sample and Hold Time = (shtim + 1) / ADCClock
+         */
+        shtim = round_up((st->sample_hold_time * adc_clk /
+                          1000000) - 1, 1);
+
         reg = AT91_ADC_PRESCAL_(prsc) & AT91_ADC_PRESCAL;
         reg |= AT91_ADC_STARTUP_(ticks) & AT91_ADC_STARTUP;
         if (st->low_res)
                 reg |= AT91_ADC_LOWRES;
         if (st->sleep_mode)
                 reg |= AT91_ADC_SLEEP;
+        reg |= AT91_ADC_SHTIM_(shtim) & AT91_ADC_SHTIM;
         at91_adc_writel(st, AT91_ADC_MR, reg);
 
         /* Setup the ADC channels available on the board */