Re: [PATCH v3 102/108] leds: qcom-lpg: Make use of devm_pwmchip_alloc() function

[Lee Jones <lee@kernel.org>]

On Wed, 22 Nov 2023, Uwe Kleine-König wrote:

> Hello Lee,
> 
> On Wed, Nov 22, 2023 at 11:56:21AM +0000, Lee Jones wrote:
> > On Tue, 21 Nov 2023, Uwe Kleine-König wrote:
> > 
> > > This prepares the pwm sub-driver to further changes of the pwm core
> > > outlined in the commit introducing devm_pwmchip_alloc(). There is no
> > > intended semantical change and the driver should behave as before.
> > > 
> > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > > ---
> > >  drivers/leds/rgb/leds-qcom-lpg.c | 30 +++++++++++++++++++++---------
> > >  1 file changed, 21 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
> > > index 68d82a682bf6..283227e02df6 100644
> > > --- a/drivers/leds/rgb/leds-qcom-lpg.c
> > > +++ b/drivers/leds/rgb/leds-qcom-lpg.c
> > > @@ -77,7 +77,7 @@ struct lpg {
> > >  
> > >  	struct mutex lock;
> > >  
> > > -	struct pwm_chip pwm;
> > > +	struct pwm_chip *pwm;
> > >  
> > >  	const struct lpg_data *data;
> > >  
> > > @@ -977,9 +977,15 @@ static int lpg_pattern_mc_clear(struct led_classdev *cdev)
> > >  	return lpg_pattern_clear(led);
> > >  }
> > >  
> > > +static inline struct lpg *lpg_pwm_from_chip(struct pwm_chip *chip)
> > > +{
> > > +	struct lpg **lpg = pwmchip_priv(chip);
> > > +	return *lpg;
> > > +}
> > 
> > I don't have easy-vis into the other patches, but if this is a common
> > pattern, perhaps add a generic helper in <linux/pwm.h>?
> > 
> > >  static int lpg_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
> > >  {
> > > -	struct lpg *lpg = container_of(chip, struct lpg, pwm);
> > > +	struct lpg *lpg = lpg_pwm_from_chip(chip);
> > >  	struct lpg_channel *chan = &lpg->channels[pwm->hwpwm];
> > >  
> > >  	return chan->in_use ? -EBUSY : 0;
> > > [...]
> > > @@ -1089,13 +1095,19 @@ static const struct pwm_ops lpg_pwm_ops = {
> > >  
> > >  static int lpg_add_pwm(struct lpg *lpg)
> > >  {
> > > +	struct pwm_chip *chip;
> > >  	int ret;
> > >  
> > > -	lpg->pwm.dev = lpg->dev;
> > > -	lpg->pwm.npwm = lpg->num_channels;
> > > -	lpg->pwm.ops = &lpg_pwm_ops;
> > > +	lpg->pwm = chip = devm_pwmchip_alloc(lpg->dev, lpg->num_channels,
> > > +					     sizeof(&lpg));
> > > +	if (IS_ERR(chip))
> > > +		return PTR_ERR(chip);
> > >  
> > > -	ret = pwmchip_add(&lpg->pwm);
> > > +	*(struct lpg **)pwmchip_priv(chip) = lpg;
> > 
> > This is vile!
> 
> This is indeed one of the uglier conversions. It gets a bit prettier
> with the following addon patch:
> 
> diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
> index 283227e02df6..e09eba823057 100644
> --- a/drivers/leds/rgb/leds-qcom-lpg.c
> +++ b/drivers/leds/rgb/leds-qcom-lpg.c
> @@ -206,6 +206,10 @@ struct lpg_data {
>  	const struct lpg_channel_data *channels;
>  };
>  
> +struct lpg_pwm_data {
> +	struct lpg *lpg;
> +};
> +
>  static int triled_set(struct lpg *lpg, unsigned int mask, unsigned int enable)
>  {
>  	/* Skip if we don't have a triled block */
> @@ -979,8 +983,9 @@ static int lpg_pattern_mc_clear(struct led_classdev *cdev)
>  
>  static inline struct lpg *lpg_pwm_from_chip(struct pwm_chip *chip)
>  {
> -	struct lpg **lpg = pwmchip_priv(chip);
> -	return *lpg;
> +	struct lpg_pwm_data *lpg_pwm_data = pwmchip_priv(chip);
> +
> +	return lpg_pwm_data->lpg;
>  }
>  
>  static int lpg_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
> @@ -1096,14 +1101,16 @@ static const struct pwm_ops lpg_pwm_ops = {
>  static int lpg_add_pwm(struct lpg *lpg)
>  {
>  	struct pwm_chip *chip;
> +	struct lpg_pwm_data *lpg_pwm_data;
>  	int ret;
>  
>  	lpg->pwm = chip = devm_pwmchip_alloc(lpg->dev, lpg->num_channels,
> -					     sizeof(&lpg));
> +					     sizeof(*lpg_pwm_data));
>  	if (IS_ERR(chip))
>  		return PTR_ERR(chip);
>  
> -	*(struct lpg **)pwmchip_priv(chip) = lpg;
> +	lpg_pwm_data = pwmchip_priv(chip);
> +	lpg_pwm_data->lpg = lpg;
>  
>  	chip->ops = &lpg_pwm_ops;
>  
> Would you like it better then?

It's definitely nicer to read and more in-line with the style I expect,
but the additional wrapper/abstraction layer is still bothersome.

-- 
Lee Jones [李琼斯]