Re: [PATCH] backlight: lm3630a: convert to atomic PWM API and check for errors

[Daniel Thompson <daniel.thompson@linaro.org>]

On Fri, Jun 18, 2021 at 10:58:44AM +0200, Uwe Kleine-König wrote:
> The practical upside here is that this only needs a single API call to
> program the hardware which (depending on the underlaying hardware) can
> be more effective and prevents glitches.
> 
> Up to now the return value of the pwm functions was ignored. Fix this
> and propagate the error to the caller.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

New code looks OK but these changes reveal just how crazy the return codes
from this driver's update_status() methods are since now the new (PWM) error path is
structured completely differently to the existing (I2C) error path.

update_status() should return 0 on success and a -ve errno otherwise.

Thus the new code to return -errno is correct and so is the I2C success
code path. However the PWM success path and the I2C error path are both
broken.

Are you OK to add a patch *before* this one to fix the existing code
paths before making the PWM changes?


Daniel.

> ---
>  drivers/video/backlight/lm3630a_bl.c | 33 +++++++++++++++-------------
>  1 file changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
> index e88a2b0e5904..24fa7e6938fa 100644
> --- a/drivers/video/backlight/lm3630a_bl.c
> +++ b/drivers/video/backlight/lm3630a_bl.c
> @@ -52,6 +52,7 @@ struct lm3630a_chip {
>  	struct gpio_desc *enable_gpio;
>  	struct regmap *regmap;
>  	struct pwm_device *pwmd;
> +	struct pwm_state pwmd_state;
>  };
>  
>  /* i2c access */
> @@ -167,16 +168,19 @@ static int lm3630a_intr_config(struct lm3630a_chip *pchip)
>  	return rval;
>  }
>  
> -static void lm3630a_pwm_ctrl(struct lm3630a_chip *pchip, int br, int br_max)
> +static int lm3630a_pwm_ctrl(struct lm3630a_chip *pchip, int br, int br_max)
>  {
> -	unsigned int period = pchip->pdata->pwm_period;
> -	unsigned int duty = br * period / br_max;
> +	int err;
>  
> -	pwm_config(pchip->pwmd, duty, period);
> -	if (duty)
> -		pwm_enable(pchip->pwmd);
> -	else
> -		pwm_disable(pchip->pwmd);
> +	pchip->pwmd_state.period = pchip->pdata->pwm_period;
> +
> +	err = pwm_set_relative_duty_cycle(&pchip->pwmd_state, br, br_max);
> +	if (err)
> +		return err;
> +
> +	pchip->pwmd_state.enabled = pchip->pwmd_state.duty_cycle ? true : false;
> +
> +	return pwm_apply_state(pchip->pwmd, &pchip->pwmd_state);
>  }
>  
>  /* update and get brightness */
> @@ -188,8 +192,11 @@ static int lm3630a_bank_a_update_status(struct backlight_device *bl)
>  
>  	/* pwm control */
>  	if ((pwm_ctrl & LM3630A_PWM_BANK_A) != 0) {
> -		lm3630a_pwm_ctrl(pchip, bl->props.brightness,
> -				 bl->props.max_brightness);
> +		ret = lm3630a_pwm_ctrl(pchip, bl->props.brightness,
> +				       bl->props.max_brightness);
> +		if (ret)
> +			return ret;
> +
>  		return bl->props.brightness;
>  	}
>  
> @@ -563,11 +570,7 @@ static int lm3630a_probe(struct i2c_client *client,
>  			return PTR_ERR(pchip->pwmd);
>  		}
>  
> -		/*
> -		 * FIXME: pwm_apply_args() should be removed when switching to
> -		 * the atomic PWM API.
> -		 */
> -		pwm_apply_args(pchip->pwmd);
> +		pwm_init_state(pchip->pwmd, &pchip->pwmd_state);
>  	}
>  
>  	/* interrupt enable  : irq 0 is not allowed */
> -- 
> 2.30.2
>