Re: [PATCH v1 1/2] iio: adc: Determine sampling frequencies by using minimum sample time

From: maitysanchayan
Date: Wed Jun 17 2015 - 06:36:13 EST

Hello,

On 15-06-14 12:16:07, Jonathan Cameron wrote:
> On 08/06/15 18:51, Rob Herring wrote:
> > On Mon, Jun 8, 2015 at 12:42 AM, Sanchayan Maity
> > <maitysanchayan@xxxxxxxxx> wrote:
> >> The driver currently does not take into account the minimum sample time
> >> as per the Figure 6-8 Chapter 9.1.1 12-bit ADC electrical characteristics.
> >> We set a static amount of cycles instead of considering the sample time as
> >> a given value, which depends on hardware characteristics.
> >>
> >> Determine sampling frequencies by first reading the device tree property
> >> node and then calculating the required Long Sample Time Adder (LSTAdder)
> >> value based on the ADC clock frequency and sample time value obtained
> >> from the device tree, this LSTAdder value is then used for calculating
> >> the sampling frequencies possible.
> >>
> >> Signed-off-by: Sanchayan Maity <maitysanchayan@xxxxxxxxx>
> >> ---
> >> .../devicetree/bindings/iio/adc/vf610-adc.txt | 6 ++
> >> drivers/iio/adc/vf610_adc.c | 74 ++++++++++++++++++++--
> >> 2 files changed, 76 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt b/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt
> >> index 3eb40e2..4419126 100644
> >> --- a/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt
> >> +++ b/Documentation/devicetree/bindings/iio/adc/vf610-adc.txt
> >> @@ -17,6 +17,11 @@ Recommended properties:
> >> - Frequency in normal mode (ADLPC=0, ADHSC=0)
> >> - Frequency in high-speed mode (ADLPC=0, ADHSC=1)
> >> - Frequency in low-power mode (ADLPC=1, ADHSC=0)
> >> + - fsl,min-sample-time: Minimum sampling time in nanoseconds. This value has
> >
> > Add a "-ns' suffix.
> >
> > Seems like this could be a common ADC property.
> Could be but so far this is a first I think...
>
> Obviously there are constraints on when you'll get a 'good' answer from any
> ADC but often they are not so well defined in the datasheets as we have here.
>
> Having said that, certainly could turn up elsewhere so I've no problem with
> having it as normal (non vendor specific) property.

Will change this to a non vendor specific property and send v2.

Thanks for the review.

Regards,
Sanchayan.

> >
> >> + to be chosen according to the conversion mode and the connected analog
> >> + source resistance (R_as) and capacitance (C_as). Refer the datasheet's
> >> + operating requirements. A safe default across a wide range of R_as and
> >> + C_as as well as conversion modes is 1000ns.
> >>
> >> Example:
> >> adc0: adc@4003b000 {
> >> @@ -27,5 +32,6 @@ adc0: adc@4003b000 {
> >> clock-names = "adc";
> >> fsl,adck-max-frequency = <30000000>, <40000000>,
> >> <20000000>;
> >> + fsl,min-sample-time = <1000>;
> >> vref-supply = <&reg_vcc_3v3_mcu>;
> >> };
> >> diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c
> >> index 480f335..bcae8fd 100644
> >> --- a/drivers/iio/adc/vf610_adc.c
> >> +++ b/drivers/iio/adc/vf610_adc.c
> >> @@ -68,6 +68,9 @@
> >> #define VF610_ADC_CLK_DIV8 0x60
> >> #define VF610_ADC_CLK_MASK 0x60
> >> #define VF610_ADC_ADLSMP_LONG 0x10
> >> +#define VF610_ADC_ADSTS_SHORT 0x100
> >> +#define VF610_ADC_ADSTS_NORMAL 0x200
> >> +#define VF610_ADC_ADSTS_LONG 0x300
> >> #define VF610_ADC_ADSTS_MASK 0x300
> >> #define VF610_ADC_ADLPC_EN 0x80
> >> #define VF610_ADC_ADHSC_EN 0x400
> >> @@ -124,6 +127,17 @@ enum conversion_mode_sel {
> >> VF610_ADC_CONV_LOW_POWER,
> >> };
> >>
> >> +enum lst_adder_sel {
> >> + VF610_ADCK_CYCLES_3,
> >> + VF610_ADCK_CYCLES_5,
> >> + VF610_ADCK_CYCLES_7,
> >> + VF610_ADCK_CYCLES_9,
> >> + VF610_ADCK_CYCLES_13,
> >> + VF610_ADCK_CYCLES_17,
> >> + VF610_ADCK_CYCLES_21,
> >> + VF610_ADCK_CYCLES_25,
> >> +};
> >> +
> >> struct vf610_adc_feature {
> >> enum clk_sel clk_sel;
> >> enum vol_ref vol_ref;
> >> @@ -132,6 +146,8 @@ struct vf610_adc_feature {
> >> int clk_div;
> >> int sample_rate;
> >> int res_mode;
> >> + u32 lst_adder_index;
> >> + u32 default_sample_time;
> >>
> >> bool calibration;
> >> bool ovwren;
> >> @@ -155,11 +171,13 @@ struct vf610_adc {
> >> };
> >>
> >> static const u32 vf610_hw_avgs[] = { 1, 4, 8, 16, 32 };
> >> +static const u32 vf610_lst_adder[] = { 3, 5, 7, 9, 13, 17, 21, 25 };
> >>
> >> static inline void vf610_adc_calculate_rates(struct vf610_adc *info)
> >> {
> >> struct vf610_adc_feature *adc_feature = &info->adc_feature;
> >> unsigned long adck_rate, ipg_rate = clk_get_rate(info->clk);
> >> + u32 adck_period, lst_addr_min;
> >> int divisor, i;
> >>
> >> adck_rate = info->max_adck_rate[adc_feature->conv_mode];
> >> @@ -174,6 +192,19 @@ static inline void vf610_adc_calculate_rates(struct vf610_adc *info)
> >> }
> >>
> >> /*
> >> + * Determine the long sample time adder value to be used based
> >> + * on the default minimum sample time provided.
> >> + */
> >> + adck_period = NSEC_PER_SEC / adck_rate;
> >> + lst_addr_min = adc_feature->default_sample_time / adck_period;
> >> + for (i = 0; i < ARRAY_SIZE(vf610_lst_adder); i++) {
> >> + if (vf610_lst_adder[i] > lst_addr_min) {
> >> + adc_feature->lst_adder_index = i;
> >> + break;
> >> + }
> >> + }
> >> +
> >> + /*
> >> * Calculate ADC sample frequencies
> >> * Sample time unit is ADCK cycles. ADCK clk source is ipg clock,
> >> * which is the same as bus clock.
> >> @@ -182,12 +213,13 @@ static inline void vf610_adc_calculate_rates(struct vf610_adc *info)
> >> * SFCAdder: fixed to 6 ADCK cycles
> >> * AverageNum: 1, 4, 8, 16, 32 samples for hardware average.
> >> * BCT (Base Conversion Time): fixed to 25 ADCK cycles for 12 bit mode
> >> - * LSTAdder(Long Sample Time): fixed to 3 ADCK cycles
> >> + * LSTAdder(Long Sample Time): 3, 5, 7, 9, 13, 17, 21, 25 ADCK cycles
> >> */
> >> adck_rate = ipg_rate / info->adc_feature.clk_div;
> >> for (i = 0; i < ARRAY_SIZE(vf610_hw_avgs); i++)
> >> info->sample_freq_avail[i] =
> >> - adck_rate / (6 + vf610_hw_avgs[i] * (25 + 3));
> >> + adck_rate / (6 + vf610_hw_avgs[i] *
> >> + (25 + vf610_lst_adder[adc_feature->lst_adder_index]));
> >> }
> >>
> >> static inline void vf610_adc_cfg_init(struct vf610_adc *info)
> >> @@ -347,8 +379,40 @@ static void vf610_adc_sample_set(struct vf610_adc *info)
> >> break;
> >> }
> >>
> >> - /* Use the short sample mode */
> >> - cfg_data &= ~(VF610_ADC_ADLSMP_LONG | VF610_ADC_ADSTS_MASK);
> >> + /*
> >> + * Set ADLSMP and ADSTS based on the Long Sample Time Adder value
> >> + * determined.
> >> + */
> >> + switch (adc_feature->lst_adder_index) {
> >> + case VF610_ADCK_CYCLES_3:
> >> + break;
> >> + case VF610_ADCK_CYCLES_5:
> >> + cfg_data |= VF610_ADC_ADSTS_SHORT;
> >> + break;
> >> + case VF610_ADCK_CYCLES_7:
> >> + cfg_data |= VF610_ADC_ADSTS_NORMAL;
> >> + break;
> >> + case VF610_ADCK_CYCLES_9:
> >> + cfg_data |= VF610_ADC_ADSTS_LONG;
> >> + break;
> >> + case VF610_ADCK_CYCLES_13:
> >> + cfg_data |= VF610_ADC_ADLSMP_LONG;
> >> + break;
> >> + case VF610_ADCK_CYCLES_17:
> >> + cfg_data |= VF610_ADC_ADLSMP_LONG;
> >> + cfg_data |= VF610_ADC_ADSTS_SHORT;
> >> + break;
> >> + case VF610_ADCK_CYCLES_21:
> >> + cfg_data |= VF610_ADC_ADLSMP_LONG;
> >> + cfg_data |= VF610_ADC_ADSTS_NORMAL;
> >> + break;
> >> + case VF610_ADCK_CYCLES_25:
> >> + cfg_data |= VF610_ADC_ADLSMP_LONG;
> >> + cfg_data |= VF610_ADC_ADSTS_NORMAL;
> >> + break;
> >> + default:
> >> + dev_err(info->dev, "error in sample time select\n");
> >> + }
> >>
> >> /* update hardware average selection */
> >> cfg_data &= ~VF610_ADC_AVGS_MASK;
> >> @@ -712,6 +776,8 @@ static int vf610_adc_probe(struct platform_device *pdev)
> >>
> >> of_property_read_u32_array(pdev->dev.of_node, "fsl,adck-max-frequency",
> >> info->max_adck_rate, 3);
> >> + of_property_read_u32(pdev->dev.of_node, "fsl,min-sample-time",
> >> + &info->adc_feature.default_sample_time);
> >>
> >> platform_set_drvdata(pdev, indio_dev);
> >>
> >> --
> >> 2.4.2
> >>
> > --
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> >
>
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