linux-kernel - Re: [PATCH] pwm-backlight: Pinctrl-fy

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Date:	Fri, 9 Nov 2012 09:06:04 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Pantelis Antoniou <panto@...oniou-consulting.com>
Cc:	Richard Purdie <rpurdie@...ys.net>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Koen Kooi <koen@...inion.thruhere.net>,
	Matt Porter <mporter@...com>, Russ Dill <Russ.Dill@...com>,
	linux-omap@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] pwm-backlight: Pinctrl-fy

On Wed, Oct 31, 2012 at 05:57:27PM +0200, Pantelis Antoniou wrote:
> Enable pinctrl for pwm-backlight.
> 
> Signed-off-by: Pantelis Antoniou <panto@...oniou-consulting.com>
> ---
>  drivers/video/backlight/pwm_bl.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index 0c91023..f3b6194 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -20,6 +20,8 @@
>  #include <linux/pwm.h>
>  #include <linux/pwm_backlight.h>
>  #include <linux/slab.h>
> +#include <linux/pinctrl/consumer.h>
> +#include <linux/err.h>
>  
>  struct pwm_bl_data {
>  	struct pwm_device	*pwm;
> @@ -180,9 +182,14 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  	struct backlight_properties props;
>  	struct backlight_device *bl;
>  	struct pwm_bl_data *pb;
> +	struct pinctrl *pinctrl;
>  	unsigned int max;
>  	int ret;
>  
> +	pinctrl = devm_pinctrl_get_select_default(&pdev->dev);
> +	if (IS_ERR(pinctrl))
> +		dev_warn(&pdev->dev, "unable to select pin group\n");
> +

I just saw this done in a similar way in some other driver and then
remembered your patch. When I reviewed this I wasn't sure if a warning
was good enough in this case. I've checked the kernel tree and it seems
like a majority handled this as failure instead of a warning. I took a
look at the pinctrl core and it seems like indeed if neither pinctrl is
enabled or if there isn't actually a pinmux configuration for a device,
then devm_pinctrl_get_select_default() will actually not return an
error, so in those cases where an error is returned it should actually
be handled as a fatal error.

I'm Cc'ing Linus Walleij, maybe he knows what to do.

Thierry

>  	if (!data) {
>  		ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
>  		if (ret < 0) {
> -- 
> 1.7.12
> 
> 
> 

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