On 11:55 Thu 20 Dec , Maxime Ripard wrote:
> 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?
you must this is hardware specific it depend on the line capacity
Best Regards,
J.
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