Re: [PATCH 3/4] IIO: Ingenic JZ47xx: Set clock divider on probe

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 23 Jun 2019 20:47:31 +0200
Artur Rojek <contact@artur-rojek.eu> wrote:

> From: Maarten ter Huurne <maarten@treewalker.org>
> 
> The SADC component can run at up to 8 MHz on JZ4725B, but is fed
> a 12 MHz input clock (EXT). Divide it by two to get 6 MHz, then
> set up another divider to match, to produce a 10us clock.
> 
> If the clock dividers are left on their power-on defaults (a divider
> of 1), the SADC mostly works, but will occasionally produce erroneous
> readings. This led to button presses being detected out of nowhere on
> the RS90 every few minutes. With this change, no ghost button presses
> were logged in almost a day worth of testing.
> 
> The ADCLK register for configuring clock dividers doesn't exist on
> JZ4740, so avoid writing it there.
> 
> A function has been introduced rather than a flag because there is a lot
> of variation between the ADCLK registers on JZ47xx SoCs, both in
> the internal layout of the register and in the frequency range
> supported by the SADC. So this solution should make it easier
> to add support for other JZ47xx SoCs later.
> 
> Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
> Signed-off-by: Artur Rojek <contact@artur-rojek.eu>
This sounds like it perhaps should be marked as a fix and have appropriate
fixes tag?  Otherwise, looks fine to me.

Jonathan

> ---
>  drivers/iio/adc/ingenic-adc.c | 54 +++++++++++++++++++++++++++++++++++
>  1 file changed, 54 insertions(+)
> 
> diff --git a/drivers/iio/adc/ingenic-adc.c b/drivers/iio/adc/ingenic-adc.c
> index 92b1d5037ac9..e234970b7150 100644
> --- a/drivers/iio/adc/ingenic-adc.c
> +++ b/drivers/iio/adc/ingenic-adc.c
> @@ -11,6 +11,7 @@
>  #include <linux/iio/iio.h>
>  #include <linux/io.h>
>  #include <linux/iopoll.h>
> +#include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
>  #include <linux/platform_device.h>
> @@ -22,8 +23,11 @@
>  #define JZ_ADC_REG_ADTCH		0x18
>  #define JZ_ADC_REG_ADBDAT		0x1c
>  #define JZ_ADC_REG_ADSDAT		0x20
> +#define JZ_ADC_REG_ADCLK		0x28
>  
>  #define JZ_ADC_REG_CFG_BAT_MD		BIT(4)
> +#define JZ_ADC_REG_ADCLK_CLKDIV_LSB	0
> +#define JZ_ADC_REG_ADCLK_CLKDIV10US_LSB	16
>  
>  #define JZ_ADC_AUX_VREF				3300
>  #define JZ_ADC_AUX_VREF_BITS			12
> @@ -34,6 +38,8 @@
>  #define JZ4740_ADC_BATTERY_HIGH_VREF		(7500 * 0.986)
>  #define JZ4740_ADC_BATTERY_HIGH_VREF_BITS	12
>  
> +struct ingenic_adc;
> +
>  struct ingenic_adc_soc_data {
>  	unsigned int battery_high_vref;
>  	unsigned int battery_high_vref_bits;
> @@ -41,6 +47,7 @@ struct ingenic_adc_soc_data {
>  	size_t battery_raw_avail_size;
>  	const int *battery_scale_avail;
>  	size_t battery_scale_avail_size;
> +	int (*init_clk_div)(struct device *dev, struct ingenic_adc *adc);
>  };
>  
>  struct ingenic_adc {
> @@ -151,6 +158,42 @@ static const int jz4740_adc_battery_scale_avail[] = {
>  	JZ_ADC_BATTERY_LOW_VREF, JZ_ADC_BATTERY_LOW_VREF_BITS,
>  };
>  
> +static int jz4725b_adc_init_clk_div(struct device *dev, struct ingenic_adc *adc)
> +{
> +	struct clk *parent_clk;
> +	unsigned long parent_rate, rate;
> +	unsigned int div_main, div_10us;
> +
> +	parent_clk = clk_get_parent(adc->clk);
> +	if (!parent_clk) {
> +		dev_err(dev, "ADC clock has no parent\n");
> +		return -ENODEV;
> +	}
> +	parent_rate = clk_get_rate(parent_clk);
> +
> +	/*
> +	 * The JZ4725B ADC works at 500 kHz to 8 MHz.
> +	 * We pick the highest rate possible.
> +	 * In practice we typically get 6 MHz, half of the 12 MHz EXT clock.
> +	 */
> +	div_main = DIV_ROUND_UP(parent_rate, 8000000);
> +	div_main = clamp(div_main, 1u, 64u);
> +	rate = parent_rate / div_main;
> +	if (rate < 500000 || rate > 8000000) {
> +		dev_err(dev, "No valid divider for ADC main clock\n");
> +		return -EINVAL;
> +	}
> +
> +	/* We also need a divider that produces a 10us clock. */
> +	div_10us = DIV_ROUND_UP(rate, 100000);
> +
> +	writel(((div_10us - 1) << JZ_ADC_REG_ADCLK_CLKDIV10US_LSB) |
> +	       (div_main - 1) << JZ_ADC_REG_ADCLK_CLKDIV_LSB,
> +	       adc->base + JZ_ADC_REG_ADCLK);
> +
> +	return 0;
> +}
> +
>  static const struct ingenic_adc_soc_data jz4725b_adc_soc_data = {
>  	.battery_high_vref = JZ4725B_ADC_BATTERY_HIGH_VREF,
>  	.battery_high_vref_bits = JZ4725B_ADC_BATTERY_HIGH_VREF_BITS,
> @@ -158,6 +201,7 @@ static const struct ingenic_adc_soc_data jz4725b_adc_soc_data = {
>  	.battery_raw_avail_size = ARRAY_SIZE(jz4725b_adc_battery_raw_avail),
>  	.battery_scale_avail = jz4725b_adc_battery_scale_avail,
>  	.battery_scale_avail_size = ARRAY_SIZE(jz4725b_adc_battery_scale_avail),
> +	.init_clk_div = jz4725b_adc_init_clk_div,
>  };
>  
>  static const struct ingenic_adc_soc_data jz4740_adc_soc_data = {
> @@ -167,6 +211,7 @@ static const struct ingenic_adc_soc_data jz4740_adc_soc_data = {
>  	.battery_raw_avail_size = ARRAY_SIZE(jz4740_adc_battery_raw_avail),
>  	.battery_scale_avail = jz4740_adc_battery_scale_avail,
>  	.battery_scale_avail_size = ARRAY_SIZE(jz4740_adc_battery_scale_avail),
> +	.init_clk_div = NULL, /* no ADCLK register on JZ4740 */
>  };
>  
>  static int ingenic_adc_read_avail(struct iio_dev *iio_dev,
> @@ -317,6 +362,15 @@ static int ingenic_adc_probe(struct platform_device *pdev)
>  		return ret;
>  	}
>  
> +	/* Set clock dividers. */
> +	if (soc_data->init_clk_div) {
> +		ret = soc_data->init_clk_div(dev, adc);
> +		if (ret) {
> +			clk_disable_unprepare(adc->clk);
> +			return ret;
> +		}
> +	}
> +
>  	/* Put hardware in a known passive state. */
>  	writeb(0x00, adc->base + JZ_ADC_REG_ENABLE);
>  	writeb(0xff, adc->base + JZ_ADC_REG_CTRL);