Hi,
Le 19/12/2012 19:37, Jean-Christophe PLAGNIOL-VILLARD a écrit :
> 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 <plagnioj@xxxxxxxxxxxx>
> Cc: linux-iio@xxxxxxxxxxxxxxx
> Cc: Nicolas Ferre <nicolas.ferre@xxxxxxxxx>
> Cc: Ludovic Desroches <ludovic.desroches@xxxxxxxxx>
> ---
> Documentation/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 efb6f02..dd2ca90 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,atmel,adc-sleep-mode: Boolean to enable of sleep mode when no conversion
> + - atmel,adc-sample-hold-time: Sample and Hold Time
In which unit? nanoseconds? number of clock ticks?
>
> Optional trigger Nodes:
> - Required properties:
> diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
> index c563488..9481375 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 __devinit 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 __devinit 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);
> +
Since, from all the datasheet I have (G20, G45 and X5), the minimum time
is always 500ns, do we really need to add a dt property for that?
Maxime
--
Maxime Ripard, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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