Re: [PATCH v2] pwm: img: Impose upper and lower timebase steps value

[Ezequiel Garcia <ezequiel.garcia@imgtec.com>]

Thierry,

On 05/08/2015 06:47 PM, Ezequiel Garcia wrote:
> From: Naidu Tellapati <naidu.tellapati@imgtec.com>
> 
> The PWM hardware on Pistachio platform has a maximum timebase steps
> value to 255. To fix it, let's introduce a compatible-specific
> data structure to contain the SoC-specific details and use it to
> specify a maximum timebase.
> 
> Also, let's limit the minimum timebase to 16 steps, to allow a sane
> range of duty cycle steps.
> 
> Fixes: 277bb6a29e00 ("pwm: Imagination Technologies PWM DAC driver")
> Signed-off-by: Naidu Tellapati <naidu.tellapati@imgtec.com>
> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
> ---
> This patch is needed for the pwm-img to work properly, so it should be
> pushed as a v4.1-rc fix.
> 

Any chance you push this patch as a fix for v4.1?

Thanks!

> Changes from v1:
> 
>  * After some investigation, we found the hardware has no lower limit
>    for the timebase. However, it still makes sense to have limit it,
>    to allow a sane duty cycle resolution. Updated the commit log and added
>    some comments to the driver explaining this.
> 
>  * Minor style fixes.
> 
>  drivers/pwm/pwm-img.c | 76 +++++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 64 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-img.c b/drivers/pwm/pwm-img.c
> index 476171a..8a029f9 100644
> --- a/drivers/pwm/pwm-img.c
> +++ b/drivers/pwm/pwm-img.c
> @@ -16,6 +16,7 @@
>  #include <linux/mfd/syscon.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> +#include <linux/of_device.h>
>  #include <linux/platform_device.h>
>  #include <linux/pwm.h>
>  #include <linux/regmap.h>
> @@ -38,7 +39,22 @@
>  #define PERIP_PWM_PDM_CONTROL_CH_MASK		0x1
>  #define PERIP_PWM_PDM_CONTROL_CH_SHIFT(ch)	((ch) * 4)
>  
> -#define MAX_TMBASE_STEPS			65536
> +/*
> + * PWM period is specified with a timebase register,
> + * in number of step periods. The PWM duty cycle is also
> + * specified in step periods, in the [0, $timebase] range.
> + * In other words, the timebase imposes the duty cycle
> + * resolution. Therefore, let's constraint the timebase to
> + * a minimum value to allow a sane range of duty cycle values.
> + * Imposing a minimum timebase, will impose a maximum PWM frequency.
> + *
> + * The value chosen is completely arbitrary.
> + */
> +#define MIN_TMBASE_STEPS			16
> +
> +struct img_pwm_soc_data {
> +	u32 max_timebase;
> +};
>  
>  struct img_pwm_chip {
>  	struct device	*dev;
> @@ -47,6 +63,9 @@ struct img_pwm_chip {
>  	struct clk	*sys_clk;
>  	void __iomem	*base;
>  	struct regmap	*periph_regs;
> +	int		max_period_ns;
> +	int		min_period_ns;
> +	const struct img_pwm_soc_data   *data;
>  };
>  
>  static inline struct img_pwm_chip *to_img_pwm_chip(struct pwm_chip *chip)
> @@ -72,24 +91,31 @@ static int img_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  	u32 val, div, duty, timebase;
>  	unsigned long mul, output_clk_hz, input_clk_hz;
>  	struct img_pwm_chip *pwm_chip = to_img_pwm_chip(chip);
> +	unsigned int max_timebase = pwm_chip->data->max_timebase;
> +
> +	if (period_ns < pwm_chip->min_period_ns ||
> +	    period_ns > pwm_chip->max_period_ns) {
> +		dev_err(chip->dev, "configured period not in range\n");
> +		return -ERANGE;
> +	}
>  
>  	input_clk_hz = clk_get_rate(pwm_chip->pwm_clk);
>  	output_clk_hz = DIV_ROUND_UP(NSEC_PER_SEC, period_ns);
>  
>  	mul = DIV_ROUND_UP(input_clk_hz, output_clk_hz);
> -	if (mul <= MAX_TMBASE_STEPS) {
> +	if (mul <= max_timebase) {
>  		div = PWM_CTRL_CFG_NO_SUB_DIV;
>  		timebase = DIV_ROUND_UP(mul, 1);
> -	} else if (mul <= MAX_TMBASE_STEPS * 8) {
> +	} else if (mul <= max_timebase * 8) {
>  		div = PWM_CTRL_CFG_SUB_DIV0;
>  		timebase = DIV_ROUND_UP(mul, 8);
> -	} else if (mul <= MAX_TMBASE_STEPS * 64) {
> +	} else if (mul <= max_timebase * 64) {
>  		div = PWM_CTRL_CFG_SUB_DIV1;
>  		timebase = DIV_ROUND_UP(mul, 64);
> -	} else if (mul <= MAX_TMBASE_STEPS * 512) {
> +	} else if (mul <= max_timebase * 512) {
>  		div = PWM_CTRL_CFG_SUB_DIV0_DIV1;
>  		timebase = DIV_ROUND_UP(mul, 512);
> -	} else if (mul > MAX_TMBASE_STEPS * 512) {
> +	} else if (mul > max_timebase * 512) {
>  		dev_err(chip->dev,
>  			"failed to configure timebase steps/divider value\n");
>  		return -EINVAL;
> @@ -143,11 +169,27 @@ static const struct pwm_ops img_pwm_ops = {
>  	.owner = THIS_MODULE,
>  };
>  
> +static const struct img_pwm_soc_data pistachio_pwm = {
> +	.max_timebase = 255,
> +};
> +
> +static const struct of_device_id img_pwm_of_match[] = {
> +	{
> +		.compatible = "img,pistachio-pwm",
> +		.data = &pistachio_pwm,
> +	},
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, img_pwm_of_match);
> +
>  static int img_pwm_probe(struct platform_device *pdev)
>  {
>  	int ret;
> +	u64 val;
> +	unsigned long clk_rate;
>  	struct resource *res;
>  	struct img_pwm_chip *pwm;
> +	const struct of_device_id *of_dev_id;
>  
>  	pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
>  	if (!pwm)
> @@ -160,6 +202,11 @@ static int img_pwm_probe(struct platform_device *pdev)
>  	if (IS_ERR(pwm->base))
>  		return PTR_ERR(pwm->base);
>  
> +	of_dev_id = of_match_device(img_pwm_of_match, &pdev->dev);
> +	if (!of_dev_id)
> +		return -ENODEV;
> +	pwm->data = of_dev_id->data;
> +
>  	pwm->periph_regs = syscon_regmap_lookup_by_phandle(pdev->dev.of_node,
>  							   "img,cr-periph");
>  	if (IS_ERR(pwm->periph_regs))
> @@ -189,6 +236,17 @@ static int img_pwm_probe(struct platform_device *pdev)
>  		goto disable_sysclk;
>  	}
>  
> +	clk_rate = clk_get_rate(pwm->pwm_clk);
> +
> +	/* The maximum input clock divider is 512 */
> +	val = (u64)NSEC_PER_SEC * 512 * pwm->data->max_timebase;
> +	do_div(val, clk_rate);
> +	pwm->max_period_ns = val;
> +
> +	val = (u64)NSEC_PER_SEC * MIN_TMBASE_STEPS;
> +	do_div(val, clk_rate);
> +	pwm->min_period_ns = val;
> +
>  	pwm->chip.dev = &pdev->dev;
>  	pwm->chip.ops = &img_pwm_ops;
>  	pwm->chip.base = -1;
> @@ -228,12 +286,6 @@ static int img_pwm_remove(struct platform_device *pdev)
>  	return pwmchip_remove(&pwm_chip->chip);
>  }
>  
> -static const struct of_device_id img_pwm_of_match[] = {
> -	{ .compatible = "img,pistachio-pwm", },
> -	{ }
> -};
> -MODULE_DEVICE_TABLE(of, img_pwm_of_match);
> -
>  static struct platform_driver img_pwm_driver = {
>  	.driver = {
>  		.name = "img-pwm",
> 

-- 
Ezequiel