| Message ID | 1355942232-26251-3-git-send-email-plagnioj@jcrosoft.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@jcrosoft.com> > Cc: linux-iio@vger.kernel.org > Cc: Nicolas Ferre <nicolas.ferre@atmel.com> > Cc: Ludovic Desroches <ludovic.desroches@atmel.com> > --- > 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
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@jcrosoft.com> > > Cc: linux-iio@vger.kernel.org > > Cc: Nicolas Ferre <nicolas.ferre@atmel.com> > > Cc: Ludovic Desroches <ludovic.desroches@atmel.com> > > --- > > 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.
Le 20/12/2012 13:49, Jean-Christophe PLAGNIOL-VILLARD a écrit : > On 11:55 Thu 20 Dec , Maxime Ripard wrote: >> 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 Ok, I see. The comment about adding the unit in the documentation is still valid though. Maxime
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 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); + 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 */
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@jcrosoft.com> Cc: linux-iio@vger.kernel.org Cc: Nicolas Ferre <nicolas.ferre@atmel.com> Cc: Ludovic Desroches <ludovic.desroches@atmel.com> --- Documentation/devicetree/bindings/arm/atmel-adc.txt | 1 + drivers/iio/adc/at91_adc.c | 15 ++++++++++++++- 2 files changed, 15 insertions(+), 1 deletion(-)