From beca9e767e27f756d6aed9a62665e3f73546aabb Mon Sep 17 00:00:00 2001 From: Jean-Christophe PLAGNIOL-VILLARD Date: Fri, 29 Mar 2013 14:54:00 +0000 Subject: [PATCH] iio: at91_adc: fix missing Sample and Hold time On the at91_adc a minimal Sample and Hold Time is necessary for the ADC to guarantee the best converted final value between two channels selection. This time has to be programmed through the bitfield SHTIM in the Mode Register ADC_MR. Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD Signed-off-by: Ludovic Desroches Signed-off-by: Jonathan Cameron --- .../devicetree/bindings/arm/atmel-adc.txt | 1 + drivers/iio/adc/at91_adc.c | 15 ++++++++++++++- 2 files changed, 15 insertions(+), 1 deletion(-) 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 */