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-rw-r--r--Documentation/devicetree/bindings/arm/atmel-adc.txt1
-rw-r--r--drivers/iio/adc/at91_adc.c15
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 */