Re: [PATCH v2 2/2] iio: adc: sc27xx: Add ADC scale calibration

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 29 Aug 2018 14:04:05 +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>
Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> ---
> Changes from v1:
>  - Use nvmem_cell_read() instead of nvmem_cell_read_u32().
> ---
>  .../bindings/iio/adc/sprd,sc27xx-adc.txt           |    4 ++
>  drivers/iio/adc/sc27xx_adc.c                       |   74 +++++++++++++++++++-
>  2 files changed, 75 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..7940b23 100644
> --- a/drivers/iio/adc/sc27xx_adc.c
> +++ b/drivers/iio/adc/sc27xx_adc.c
> @@ -5,10 +5,12 @@
>  #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>
>  #include <linux/regmap.h>
> +#include <linux/slab.h>
>  
>  /* PMIC global registers definition */
>  #define SC27XX_MODULE_EN		0xc08
> @@ -87,16 +89,73 @@ 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 int sc27xx_adc_scale_calibration(struct sc27xx_adc_data *data,
> +					bool big_scale)
> +{
> +	const struct sc27xx_adc_linear_graph *calib_graph;
> +	struct sc27xx_adc_linear_graph *graph;
> +	struct nvmem_cell *cell;
> +	const char *cell_name;
> +	u32 calib_data = 0;
> +	void *buf;
> +	size_t len;
> +
> +	if (big_scale) {
> +		calib_graph = &big_scale_graph_calib;
> +		graph = &big_scale_graph;
> +		cell_name = "big_scale_calib";
> +	} else {
> +		calib_graph = &small_scale_graph_calib;
> +		graph = &small_scale_graph;
> +		cell_name = "small_scale_calib";
> +	}
> +
> +	cell = nvmem_cell_get(data->dev, cell_name);
> +	if (IS_ERR(cell))
> +		return PTR_ERR(cell);
> +
> +	buf = nvmem_cell_read(cell, &len);
> +	nvmem_cell_put(cell);
> +
> +	if (IS_ERR(buf))
> +		return PTR_ERR(buf);
> +
> +	memcpy(&calib_data, buf, min(len, sizeof(u32)));
> +
> +	/* 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);
> +
> +	kfree(buf);
> +	return 0;
> +}
> +
>  static int sc27xx_adc_get_ratio(int channel, int scale)
>  {
>  	switch (channel) {
> @@ -209,7 +268,7 @@ 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;
> @@ -390,6 +449,15 @@ static int sc27xx_adc_enable(struct sc27xx_adc_data *data)
>  	if (ret)
>  		goto disable_clk;
>  
> +	/* ADC channel scales' calibration from nvmem device */
> +	ret = sc27xx_adc_scale_calibration(data, true);
> +	if (ret)
> +		goto disable_clk;
> +
> +	ret = sc27xx_adc_scale_calibration(data, false);
> +	if (ret)
> +		goto disable_clk;
> +
>  	return 0;
>  
>  disable_clk:
> -- 
> 1.7.9.5
>