Hi Heiner,
sorry for the delay, I've been very busy in the last two weeks.
On Sat, Mar 4, 2017 at 5:29 PM, Heiner Kallweit <hkallweit1@xxxxxxxxx> wrote:
> The calibration on Meson GXBB is different from the one on GXM/GXL.
> This patch only supports GXBB as I don't have other spec and test hw.
> Points 25% vref and 75% vref are used for calibration.
>
> Adding a calibration scale resulted in no improvement, therefore
> only a simple calibration bias is supported.
>
> Successfully tested on a Odroid C2. Calibbias is 8 on my system.
>
> Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx>
> ---
> v2:
> - added calibration scale
your calibration code seems to work fine, I tested this on a Khadas VIM Pro.
background info:
on the Khadas VIM SAR_ADC_CH1 is wired to VCC through a resistor to
indicate the hardware version, according to the schematics [0] on page
4 the expected ADC value is 512.
512 is due to a bug in Amlogic's Linux saradc driver as it only reads
10bit (while the actual hardware supports 12bit). so actually the
expected ADC value is 2048 (512 << 2).
I confirmed this in the vendor u-boot by running "aradc_12bit open 1;
aradc_12bit read" which gives a value of approx. 2000 (u-boot's saradc
driver doesn't support calibration, so we're pretty close).
before your patch I got a value of somewhere around 2000, with your
patch I get values *very* close to 2048.
thus:
Tested-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>
some minor comments inline below
> ---
> drivers/iio/adc/meson_saradc.c | 74 ++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 72 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/adc/meson_saradc.c b/drivers/iio/adc/meson_saradc.c
> index 23710088..d5aa0d04 100644
> --- a/drivers/iio/adc/meson_saradc.c
> +++ b/drivers/iio/adc/meson_saradc.c
> @@ -173,7 +173,9 @@
> .channel = _chan, \
> .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
> BIT(IIO_CHAN_INFO_AVERAGE_RAW), \
> - .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
> + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | \
> + BIT(IIO_CHAN_INFO_CALIBBIAS) | \
> + BIT(IIO_CHAN_INFO_CALIBSCALE), \
> .datasheet_name = "SAR_ADC_CH"#_chan, \
> }
>
> @@ -233,6 +235,8 @@ struct meson_sar_adc_priv {
> struct clk *adc_div_clk;
> struct clk_divider clk_div;
> struct completion done;
> + int calibbias;
> + int calibscale;
> };
>
> static const struct regmap_config meson_sar_adc_regmap_config = {
> @@ -252,6 +256,16 @@ static unsigned int meson_sar_adc_get_fifo_count(struct iio_dev *indio_dev)
> return FIELD_GET(MESON_SAR_ADC_REG0_FIFO_COUNT_MASK, regval);
> }
>
> +static int meson_sar_adc_calib_val(struct iio_dev *indio_dev, int val)
> +{
> + struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
> + int tmp;
> +
> + tmp = div_s64((s64)val * priv->calibscale, 1000000) + priv->calibbias;
> +
> + return clamp(tmp, 0, (1 << priv->data->resolution) - 1);
> +}
> +
this logic is slightly different than in Amlogic's driver (which
basically uses "val - actual_value_of(CHAN7_MUX_VDD_DIV2)" instead of
"val"), see [1]. this does NOT mean that you have to change your code,
although it would be nice if you could add a comment how this magic^W
math works!
> static int meson_sar_adc_wait_busy_clear(struct iio_dev *indio_dev)
> {
> struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
> @@ -303,7 +317,7 @@ static int meson_sar_adc_read_raw_sample(struct iio_dev *indio_dev,
> fifo_val = FIELD_GET(MESON_SAR_ADC_FIFO_RD_SAMPLE_VALUE_MASK,
> regval);
> fifo_val &= GENMASK(priv->data->resolution - 1, 0);
> - *val = fifo_val;
> + *val = meson_sar_adc_calib_val(indio_dev, fifo_val);
>
> return 0;
> }
> @@ -529,6 +543,15 @@ static int meson_sar_adc_iio_info_read_raw(struct iio_dev *indio_dev,
> *val2 = priv->data->resolution;
> return IIO_VAL_FRACTIONAL_LOG2;
>
> + case IIO_CHAN_INFO_CALIBBIAS:
> + *val = priv->calibbias;
> + return IIO_VAL_INT;
> +
> + case IIO_CHAN_INFO_CALIBSCALE:
> + *val = priv->calibscale / 1000000;
> + *val2 = priv->calibscale % 1000000;
can we add a #define for 1000000? it's used very often in the driver
which makes it a bit hard to read.
> + return IIO_VAL_INT_PLUS_MICRO;
> +
> default:
> return -EINVAL;
> }
> @@ -754,6 +777,47 @@ static irqreturn_t meson_sar_adc_irq(int irq, void *data)
> return IRQ_HANDLED;
> }
>
> +static int meson_sar_adc_calib(struct iio_dev *indio_dev)
> +{
> + struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
> + int ret, nominal0, nominal1, value0, value1;
> +
> + /* use points 25% and 75% for calibration */
> + nominal0 = (1 << priv->data->resolution) / 4;
> + nominal1 = (1 << priv->data->resolution) * 3 / 4;
> +
> + meson_sar_adc_set_chan7_mux(indio_dev, CHAN7_MUX_VDD_DIV4);
> + usleep_range(10, 20);
> + ret = meson_sar_adc_get_sample(indio_dev,
> + &meson_sar_adc_iio_channels[7],
> + MEAN_AVERAGING, EIGHT_SAMPLES, &value0);
> + if (ret < 0)
> + goto out;
> +
> + meson_sar_adc_set_chan7_mux(indio_dev, CHAN7_MUX_VDD_MUL3_DIV4);
> + usleep_range(10, 20);
> + ret = meson_sar_adc_get_sample(indio_dev,
> + &meson_sar_adc_iio_channels[7],
> + MEAN_AVERAGING, EIGHT_SAMPLES, &value1);
> + if (ret < 0)
> + goto out;
> +
> + if (value1 <= value0) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + priv->calibscale = div_s64((nominal1 - nominal0) * 1000000LL,
> + value1 - value0);
> + priv->calibbias = nominal0 - div_s64((s64)value0 * priv->calibscale,
> + 1000000);
> + ret = 0;
> +out:
> + meson_sar_adc_set_chan7_mux(indio_dev, CHAN7_MUX_CH7_INPUT);
> +
> + return ret;
> +}
> +
> static const struct iio_info meson_sar_adc_iio_info = {
> .read_raw = meson_sar_adc_iio_info_read_raw,
> .driver_module = THIS_MODULE,
> @@ -893,6 +957,8 @@ static int meson_sar_adc_probe(struct platform_device *pdev)
> return PTR_ERR(priv->vref);
> }
>
> + priv->calibscale = 1000000;
> +
> ret = meson_sar_adc_init(indio_dev);
> if (ret)
> goto err;
> @@ -901,6 +967,10 @@ static int meson_sar_adc_probe(struct platform_device *pdev)
> if (ret)
> goto err;
>
> + ret = meson_sar_adc_calib(indio_dev);
> + if (ret)
> + goto err_hw;
> +
should we fail here if calibration did not work? we could use the
non-calibrated value as fallback (I think all that would have to be
done is changing this to not error out, as you're initializing
calibscale above already, and calibbias will be 0 by default)
> platform_set_drvdata(pdev, indio_dev);
>
> ret = iio_device_register(indio_dev);
> --
> 2.12.0
>
>
if anyone is interested in before and after statistics:
values before your patch:
/sys/bus/iio/devices/iio:device0/in_voltage0_mean_raw:3993
/sys/bus/iio/devices/iio:device0/in_voltage0_raw:4009
/sys/bus/iio/devices/iio:device0/in_voltage1_mean_raw:2001
/sys/bus/iio/devices/iio:device0/in_voltage1_raw:1992
/sys/bus/iio/devices/iio:device0/in_voltage2_mean_raw:487
/sys/bus/iio/devices/iio:device0/in_voltage2_raw:408
/sys/bus/iio/devices/iio:device0/in_voltage3_mean_raw:386
/sys/bus/iio/devices/iio:device0/in_voltage3_raw:356
/sys/bus/iio/devices/iio:device0/in_voltage4_mean_raw:466
/sys/bus/iio/devices/iio:device0/in_voltage4_raw:476
/sys/bus/iio/devices/iio:device0/in_voltage5_mean_raw:470
/sys/bus/iio/devices/iio:device0/in_voltage5_raw:469
/sys/bus/iio/devices/iio:device0/in_voltage6_mean_raw:2199
/sys/bus/iio/devices/iio:device0/in_voltage6_raw:2197
/sys/bus/iio/devices/iio:device0/in_voltage7_mean_raw:829
/sys/bus/iio/devices/iio:device0/in_voltage7_raw:492
/sys/bus/iio/devices/iio:device0/in_voltage_scale:0.439453125
/sys/bus/iio/devices/iio:device0/name:meson-gxl-saradc
values after your patch:
/sys/bus/iio/devices/iio:device0/in_voltage0_mean_raw:4095
/sys/bus/iio/devices/iio:device0/in_voltage0_raw:4095
/sys/bus/iio/devices/iio:device0/in_voltage1_mean_raw:2044
/sys/bus/iio/devices/iio:device0/in_voltage1_raw:2044
/sys/bus/iio/devices/iio:device0/in_voltage2_mean_raw:487
/sys/bus/iio/devices/iio:device0/in_voltage2_raw:404
/sys/bus/iio/devices/iio:device0/in_voltage3_mean_raw:383
/sys/bus/iio/devices/iio:device0/in_voltage3_raw:373
/sys/bus/iio/devices/iio:device0/in_voltage4_mean_raw:466
/sys/bus/iio/devices/iio:device0/in_voltage4_raw:478
/sys/bus/iio/devices/iio:device0/in_voltage5_mean_raw:470
/sys/bus/iio/devices/iio:device0/in_voltage5_raw:472
/sys/bus/iio/devices/iio:device0/in_voltage6_mean_raw:2269
/sys/bus/iio/devices/iio:device0/in_voltage6_raw:2257
/sys/bus/iio/devices/iio:device0/in_voltage7_mean_raw:837
/sys/bus/iio/devices/iio:device0/in_voltage7_raw:488
/sys/bus/iio/devices/iio:device0/in_voltage_calibbias:-12
/sys/bus/iio/devices/iio:device0/in_voltage_calibscale:1.026566
/sys/bus/iio/devices/iio:device0/in_voltage_scale:0.439453125
/sys/bus/iio/devices/iio:device0/name:meson-gxl-saradc
many thanks again for this contribution Heiner!
Regards,
Martin
[0] https://github.com/khadas/documents/blob/master/Vim_V12_Sch.pdf
[1] https://github.com/khadas/linux/blob/9ff62f1c4e333feb64bc419191215cec2c7c7c73/drivers/amlogic/input/saradc/saradc.c#L174
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