Re: [PATCH v3] backlight: pwm_bl: switch to using "atomic" PWM API

[Daniel Thompson]

On Tue, Aug 14, 2018 at 06:50:59PM +0200, Enric Balletbo i Serra wrote:
> The "atomic" API allows us to configure PWM period and duty_cycle and
> enable it in one call.
> 
> The patch also moves the pwm_init_state just before any use of the
> pwm_state struct, this fixes a potential bug where pwm_get_state
> can be called before pwm_init_state.
> 
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>

Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>

> ---
> 
> Changes in v3:
> - Get rid of duty_cycle variable from pwm_backlight_update_status.
> - Get rid of pb->enabled and use only the status.enabled variable.
> - Make power_on match power_off.
> - Do not share status between ...update_status and ...power_on
> 
> Changes in v2:
> - Do not force the PWM be off in the first call to pwm_apply_state.
> - Delayed applying the state until we know what the period is.
> - Removed pb->period as after the conversion is not needed.
> 
>  drivers/video/backlight/pwm_bl.c | 81 +++++++++++++++++---------------
>  1 file changed, 42 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index bdfcc0a71db1..678b27063198 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -28,10 +28,8 @@
>  struct pwm_bl_data {
>  	struct pwm_device	*pwm;
>  	struct device		*dev;
> -	unsigned int		period;
>  	unsigned int		lth_brightness;
>  	unsigned int		*levels;
> -	bool			enabled;
>  	struct regulator	*power_supply;
>  	struct gpio_desc	*enable_gpio;
>  	unsigned int		scale;
> @@ -46,31 +44,35 @@ struct pwm_bl_data {
>  	void			(*exit)(struct device *);
>  };
>  
> -static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)
> +static void pwm_backlight_power_on(struct pwm_bl_data *pb)
>  {
> +	struct pwm_state state;
>  	int err;
>  
> -	if (pb->enabled)
> +	pwm_get_state(pb->pwm, &state);
> +	if (state.enabled)
>  		return;
>  
>  	err = regulator_enable(pb->power_supply);
>  	if (err < 0)
>  		dev_err(pb->dev, "failed to enable power supply\n");
>  
> -	pwm_enable(pb->pwm);
> +	state.enabled = true;
> +	pwm_apply_state(pb->pwm, &state);
>  
>  	if (pb->post_pwm_on_delay)
>  		msleep(pb->post_pwm_on_delay);
>  
>  	if (pb->enable_gpio)
>  		gpiod_set_value_cansleep(pb->enable_gpio, 1);
> -
> -	pb->enabled = true;
>  }
>  
>  static void pwm_backlight_power_off(struct pwm_bl_data *pb)
>  {
> -	if (!pb->enabled)
> +	struct pwm_state state;
> +
> +	pwm_get_state(pb->pwm, &state);
> +	if (!state.enabled)
>  		return;
>  
>  	if (pb->enable_gpio)
> @@ -79,24 +81,27 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
>  	if (pb->pwm_off_delay)
>  		msleep(pb->pwm_off_delay);
>  
> -	pwm_config(pb->pwm, 0, pb->period);
> -	pwm_disable(pb->pwm);
> +	state.enabled = false;
> +	state.duty_cycle = 0;
> +	pwm_apply_state(pb->pwm, &state);
>  
>  	regulator_disable(pb->power_supply);
> -	pb->enabled = false;
>  }
>  
>  static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
>  {
>  	unsigned int lth = pb->lth_brightness;
> +	struct pwm_state state;
>  	u64 duty_cycle;
>  
> +	pwm_get_state(pb->pwm, &state);
> +
>  	if (pb->levels)
>  		duty_cycle = pb->levels[brightness];
>  	else
>  		duty_cycle = brightness;
>  
> -	duty_cycle *= pb->period - lth;
> +	duty_cycle *= state.period - lth;
>  	do_div(duty_cycle, pb->scale);
>  
>  	return duty_cycle + lth;
> @@ -106,7 +111,7 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
>  {
>  	struct pwm_bl_data *pb = bl_get_data(bl);
>  	int brightness = bl->props.brightness;
> -	int duty_cycle;
> +	struct pwm_state state;
>  
>  	if (bl->props.power != FB_BLANK_UNBLANK ||
>  	    bl->props.fb_blank != FB_BLANK_UNBLANK ||
> @@ -117,9 +122,10 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
>  		brightness = pb->notify(pb->dev, brightness);
>  
>  	if (brightness > 0) {
> -		duty_cycle = compute_duty_cycle(pb, brightness);
> -		pwm_config(pb->pwm, duty_cycle, pb->period);
> -		pwm_backlight_power_on(pb, brightness);
> +		pwm_get_state(pb->pwm, &state);
> +		state.duty_cycle = compute_duty_cycle(pb, brightness);
> +		pwm_apply_state(pb->pwm, &state);
> +		pwm_backlight_power_on(pb);
>  	} else
>  		pwm_backlight_power_off(pb);
>  
> @@ -447,7 +453,6 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  	struct device_node *node = pdev->dev.of_node;
>  	struct pwm_bl_data *pb;
>  	struct pwm_state state;
> -	struct pwm_args pargs;
>  	unsigned int i;
>  	int ret;
>  
> @@ -478,7 +483,6 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  	pb->check_fb = data->check_fb;
>  	pb->exit = data->exit;
>  	pb->dev = &pdev->dev;
> -	pb->enabled = false;
>  	pb->post_pwm_on_delay = data->post_pwm_on_delay;
>  	pb->pwm_off_delay = data->pwm_off_delay;
>  
> @@ -539,10 +543,26 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  
>  	dev_dbg(&pdev->dev, "got pwm for backlight\n");
>  
> -	if (!data->levels) {
> -		/* Get the PWM period (in nanoseconds) */
> -		pwm_get_state(pb->pwm, &state);
> +	/* Sync up PWM state. */
> +	pwm_init_state(pb->pwm, &state);
>  
> +	/*
> +	 * The DT case will set the pwm_period_ns field to 0 and store the
> +	 * period, parsed from the DT, in the PWM device. For the non-DT case,
> +	 * set the period from platform data if it has not already been set
> +	 * via the PWM lookup table.
> +	 */
> +	if (!state.period && (data->pwm_period_ns > 0))
> +		state.period = data->pwm_period_ns;
> +
> +	ret = pwm_apply_state(pb->pwm, &state);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",
> +			ret);
> +		goto err_alloc;
> +	}
> +
> +	if (!data->levels) {
>  		ret = pwm_backlight_brightness_default(&pdev->dev, data,
>  						       state.period);
>  		if (ret < 0) {
> @@ -559,24 +579,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  		pb->levels = data->levels;
>  	}
>  
> -	/*
> -	 * FIXME: pwm_apply_args() should be removed when switching to
> -	 * the atomic PWM API.
> -	 */
> -	pwm_apply_args(pb->pwm);
> -
> -	/*
> -	 * The DT case will set the pwm_period_ns field to 0 and store the
> -	 * period, parsed from the DT, in the PWM device. For the non-DT case,
> -	 * set the period from platform data if it has not already been set
> -	 * via the PWM lookup table.
> -	 */
> -	pwm_get_args(pb->pwm, &pargs);
> -	pb->period = pargs.period;
> -	if (!pb->period && (data->pwm_period_ns > 0))
> -		pb->period = data->pwm_period_ns;
> -
> -	pb->lth_brightness = data->lth_brightness * (pb->period / pb->scale);
> +	pb->lth_brightness = data->lth_brightness * (state.period / pb->scale);
>  
>  	memset(&props, 0, sizeof(struct backlight_properties));
>  	props.type = BACKLIGHT_RAW;
> -- 
> 2.18.0
>