Re: [PATCH 2/2] iio: adc: sc27xx: Add ADC scale calibration

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 24 Aug 2018 17:53:16 +0800
Baolin Wang <baolin.wang@linaro.org> wrote:

> This patch adds support to read calibration values from the eFuse
> controller to calibrate the ADC channel scales, which can make ADC
> sample data more accurate.
> 
> Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
This looks good to me.  I'll leave it for now though given open questions
on patch 1 and to allow others time to comment on this if they wish -
particularly as it includes a binding addition.

Jonathan

> ---
>  .../bindings/iio/adc/sprd,sc27xx-adc.txt           |    4 ++
>  drivers/iio/adc/sc27xx_adc.c                       |   52 ++++++++++++++++++--
>  2 files changed, 53 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/sprd,sc27xx-adc.txt b/Documentation/devicetree/bindings/iio/adc/sprd,sc27xx-adc.txt
> index 8aad960..b4daa15 100644
> --- a/Documentation/devicetree/bindings/iio/adc/sprd,sc27xx-adc.txt
> +++ b/Documentation/devicetree/bindings/iio/adc/sprd,sc27xx-adc.txt
> @@ -12,6 +12,8 @@ Required properties:
>  - interrupts: The interrupt number for the ADC device.
>  - #io-channel-cells: Number of cells in an IIO specifier.
>  - hwlocks: Reference to a phandle of a hwlock provider node.
> +- nvmem-cells: A phandle to the calibration cells provided by eFuse device.
> +- nvmem-cell-names: Should be "big_scale_calib", "small_scale_calib".
>  
>  Example:
>  
> @@ -32,5 +34,7 @@ Example:
>  			interrupts = <0 IRQ_TYPE_LEVEL_HIGH>;
>  			#io-channel-cells = <1>;
>  			hwlocks = <&hwlock 4>;
> +			nvmem-cells = <&adc_big_scale>, <&adc_small_scale>;
> +			nvmem-cell-names = "big_scale_calib", "small_scale_calib";
>  		};
>  	};
> diff --git a/drivers/iio/adc/sc27xx_adc.c b/drivers/iio/adc/sc27xx_adc.c
> index 153c311..7ac78eda 100644
> --- a/drivers/iio/adc/sc27xx_adc.c
> +++ b/drivers/iio/adc/sc27xx_adc.c
> @@ -5,6 +5,7 @@
>  #include <linux/iio/iio.h>
>  #include <linux/interrupt.h>
>  #include <linux/module.h>
> +#include <linux/nvmem-consumer.h>
>  #include <linux/of.h>
>  #include <linux/of_device.h>
>  #include <linux/platform_device.h>
> @@ -87,16 +88,48 @@ struct sc27xx_adc_linear_graph {
>   * should use the small-scale graph, and if more than 1.2v, we should use the
>   * big-scale graph.
>   */
> -static const struct sc27xx_adc_linear_graph big_scale_graph = {
> +static struct sc27xx_adc_linear_graph big_scale_graph = {
>  	4200, 3310,
>  	3600, 2832,
>  };
>  
> -static const struct sc27xx_adc_linear_graph small_scale_graph = {
> +static struct sc27xx_adc_linear_graph small_scale_graph = {
>  	1000, 3413,
>  	100, 341,
>  };
>  
> +static const struct sc27xx_adc_linear_graph big_scale_graph_calib = {
> +	4200, 856,
> +	3600, 733,
> +};
> +
> +static const struct sc27xx_adc_linear_graph small_scale_graph_calib = {
> +	1000, 833,
> +	100, 80,
> +};
> +
> +static int sc27xx_adc_get_calib_data(u32 calib_data, int calib_adc)
> +{
> +	return ((calib_data & 0xff) + calib_adc - 128) * 4;
> +}
> +
> +static void
> +sc27xx_adc_scale_calibration(const struct sc27xx_adc_linear_graph *calib_graph,
> +			     u32 calib_data, bool big_scale)
> +{
> +	struct sc27xx_adc_linear_graph *graph;
> +
> +	if (big_scale)
> +		graph = &big_scale_graph;
> +	else
> +		graph = &small_scale_graph;
> +
> +	/* Only need to calibrate the adc values in the linear graph. */
> +	graph->adc0 = sc27xx_adc_get_calib_data(calib_data, calib_graph->adc0);
> +	graph->adc1 = sc27xx_adc_get_calib_data(calib_data >> 8,
> +						calib_graph->adc1);
> +}
> +
>  static int sc27xx_adc_get_ratio(int channel, int scale)
>  {
>  	switch (channel) {
> @@ -209,7 +242,7 @@ static void sc27xx_adc_volt_ratio(struct sc27xx_adc_data *data,
>  	*div_denominator = ratio & SC27XX_RATIO_DENOMINATOR_MASK;
>  }
>  
> -static int sc27xx_adc_to_volt(const struct sc27xx_adc_linear_graph *graph,
> +static int sc27xx_adc_to_volt(struct sc27xx_adc_linear_graph *graph,
>  			      int raw_adc)
>  {
>  	int tmp;
> @@ -371,6 +404,7 @@ static int sc27xx_adc_write_raw(struct iio_dev *indio_dev,
>  
>  static int sc27xx_adc_enable(struct sc27xx_adc_data *data)
>  {
> +	u32 val;
>  	int ret;
>  
>  	ret = regmap_update_bits(data->regmap, SC27XX_MODULE_EN,
> @@ -390,6 +424,18 @@ static int sc27xx_adc_enable(struct sc27xx_adc_data *data)
>  	if (ret)
>  		goto disable_clk;
>  
> +	/* ADC channel scales' calibration from nvmem device */
> +	ret = nvmem_cell_read_u32(data->dev, "big_scale_calib", &val);
> +	if (ret)
> +		goto disable_clk;
> +
> +	sc27xx_adc_scale_calibration(&big_scale_graph_calib, val, true);
> +
> +	ret = nvmem_cell_read_u32(data->dev, "small_scale_calib", &val);
> +	if (ret)
> +		goto disable_clk;
> +
> +	sc27xx_adc_scale_calibration(&small_scale_graph_calib, val, false);
>  	return 0;
>  
>  disable_clk: