linux-kernel - Re: [PATCH v3 2/4] leds: leds-pwm: Preparing the driver for device tree support

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Date:	Tue, 11 Dec 2012 08:12:53 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	Bryan Wu <cooloney@...il.com>, Richard Purdie <rpurdie@...ys.net>,
	Grant Likely <grant.likely@...retlab.ca>,
	linux-kernel@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-doc@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: [PATCH v3 2/4] leds: leds-pwm: Preparing the driver for device
 tree support

On Mon, Dec 10, 2012 at 11:00:35AM +0100, Peter Ujfalusi wrote:
> In order to be able to add device tree support for leds-pwm driver we need
> to rearrange the data structures used by the drivers.
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> ---
>  drivers/leds/leds-pwm.c | 39 +++++++++++++++++++++++----------------
>  1 file changed, 23 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
> index 351257c..02f0c0c 100644
> --- a/drivers/leds/leds-pwm.c
> +++ b/drivers/leds/leds-pwm.c
> @@ -30,6 +30,11 @@ struct led_pwm_data {
>  	unsigned int		period;
>  };
>  
> +struct led_pwm_priv {
> +	int num_leds;
> +	struct led_pwm_data leds[];
> +};

I think you want leds[0] here. Otherwise your structure is too large by
sizeof(struct led_pwm_data *).

> +
>  static void led_pwm_set(struct led_classdev *led_cdev,
>  	enum led_brightness brightness)
>  {
> @@ -47,25 +52,29 @@ static void led_pwm_set(struct led_classdev *led_cdev,
>  	}
>  }
>  
> +static inline int sizeof_pwm_leds_priv(int num_leds)

Perhaps this should return size_t?

> +{
> +	return sizeof(struct led_pwm_priv) +
> +		      (sizeof(struct led_pwm_data) * num_leds);
> +}
> +
>  static int led_pwm_probe(struct platform_device *pdev)
>  {
>  	struct led_pwm_platform_data *pdata = pdev->dev.platform_data;
> -	struct led_pwm *cur_led;
> -	struct led_pwm_data *leds_data, *led_dat;
> +	struct led_pwm_priv *priv;
>  	int i, ret = 0;
>  
>  	if (!pdata)
>  		return -EBUSY;
>  
> -	leds_data = devm_kzalloc(&pdev->dev,
> -			sizeof(struct led_pwm_data) * pdata->num_leds,
> -				GFP_KERNEL);
> -	if (!leds_data)
> +	priv = devm_kzalloc(&pdev->dev, sizeof_pwm_leds_priv(pdata->num_leds),
> +			    GFP_KERNEL);

I'm not sure if sizeof_pwm_leds_priv() requires to be a separate
function. You could make it shorter by doing something like:

	size_t extra = sizeof(*led_dat) * pdata->num_leds;

	priv = devm_kzalloc(&pdev->dev, sizeof(*priv) + extra, GFP_KERNEL);

But that's really just a matter of taste, so no further objections if
you want to keep the inline function.

Thierry

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