linux-kernel - Re: [PATCH v4] backlight: lp855x: Switch to atomic PWM API

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Date:   Tue, 2 Nov 2021 16:00:00 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Maíra Canal <maira.canal@....br>
Cc:     lee.jones@...aro.org, jingoohan1@...il.com,
        thierry.reding@...il.com, u.kleine-koenig@...gutronix.de,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v4] backlight: lp855x: Switch to atomic PWM API

On Mon, Nov 01, 2021 at 10:19:21AM -0300, Maíra Canal wrote:
> Remove legacy PWM interface (pwm_config, pwm_enable, pwm_disable) and
> replace it for the atomic PWM API.
> 
> Signed-off-by: Maíra Canal <maira.canal@....br>
> ---
> V1 -> V2: Initialize variable and simply conditional loop
> V2 -> V3: Fix assignment of NULL variable
> V3 -> V4: Replace division for pwm_set_relative_duty_cycle
> ---
>  drivers/video/backlight/lp855x_bl.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/video/backlight/lp855x_bl.c b/drivers/video/backlight/lp855x_bl.c
> index e94932c69f54..bbf24564082a 100644
> --- a/drivers/video/backlight/lp855x_bl.c
> +++ b/drivers/video/backlight/lp855x_bl.c
> @@ -233,9 +233,8 @@ static int lp855x_configure(struct lp855x *lp)
>  
>  static void lp855x_pwm_ctrl(struct lp855x *lp, int br, int max_br)
>  {
> -	unsigned int period = lp->pdata->period_ns;
> -	unsigned int duty = br * period / max_br;
>  	struct pwm_device *pwm;
> +	struct pwm_state state;
>  
>  	/* request pwm device with the consumer name */
>  	if (!lp->pwm) {
> @@ -245,18 +244,15 @@ static void lp855x_pwm_ctrl(struct lp855x *lp, int br, int max_br)
>  
>  		lp->pwm = pwm;
>  
> -		/*
> -		 * FIXME: pwm_apply_args() should be removed when switching to
> -		 * the atomic PWM API.
> -		 */
> -		pwm_apply_args(pwm);
> +		pwm_init_state(lp->pwm, &state);
> +		state.period = lp->pdata->period_ns;
>  	}
>  
> -	pwm_config(lp->pwm, duty, period);
> -	if (duty)
> -		pwm_enable(lp->pwm);
> -	else
> -		pwm_disable(lp->pwm);
> +	pwm_get_state(lp->pwm, &state);

Should this be:

	} else {
		pwm_get_state(lp->pwm, &state);
	}

As currently written this will clobber the state.period that was set
above.


Daniel.


> +	pwm_set_relative_duty_cycle(&state, br, max_br);
> +	state.enabled = state.duty_cycle;
> +
> +	pwm_apply_state(lp->pwm, &state);
>  }
>  
>  static int lp855x_bl_update_status(struct backlight_device *bl)
> -- 
> 2.31.1
>