linux-kernel - Re: [RFT][PATCH v2] backlight: 88pm860x_bl: Add missing of_node

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Date:	Mon, 4 Feb 2013 21:42:42 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	Axel Lin <axel.lin@...ics.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Purdie <rpurdie@...ys.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFT][PATCH v2] backlight: 88pm860x_bl: Add missing of_node_put()

On Sun, Jan 27, 2013 at 8:58 PM, Axel Lin <axel.lin@...ics.com> wrote:
> of_find_node_by_name() returns a node pointer with refcount incremented, use
> of_node_put() on it when done.
>
> of_find_node_by_name() will call of_node_put() against the node pass to from
> parameter, thus we also need to call of_node_get(from) before calling
> of_find_node_by_name().
>
> Signed-off-by: Axel Lin <axel.lin@...ics.com>
> ---
> v2:
> need to call of_node_get(pdev->dev.parent->of_node) before calling
> of_find_node_by_name().
>
>  drivers/video/backlight/88pm860x_bl.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/video/backlight/88pm860x_bl.c b/drivers/video/backlight/88pm860x_bl.c
> index c072ed9..2cd6350 100644
> --- a/drivers/video/backlight/88pm860x_bl.c
> +++ b/drivers/video/backlight/88pm860x_bl.c
> @@ -165,8 +165,10 @@ static int pm860x_backlight_dt_init(struct platform_device *pdev,
>                                     struct pm860x_backlight_data *data,
>                                     char *name)
>  {
> -       struct device_node *nproot = pdev->dev.parent->of_node, *np;
> +       struct device_node *nproot, *np;
>         int iset = 0;
> +
> +       nproot = of_node_get(pdev->dev.parent->of_node);
>         if (!nproot)
>                 return -ENODEV;
>         nproot = of_find_node_by_name(nproot, "backlights");
> @@ -184,6 +186,7 @@ static int pm860x_backlight_dt_init(struct platform_device *pdev,
>                         break;
>                 }
>         }
> +       of_node_put(nproot);
>         return 0;
>  }
>  #else

Don't agree on this. If we want to protect it, we should use the logic in below.
1. of_node_get() in parent 88pm860x-core driver.
2. of_node_put() in child backlight driver or anything else.

The reference is used to prevent of_node releasing before some usage.
At here, we need
to prevent parent driver to release of_node. I can't see any benefit
from of_node_get()
in the child backlight driver.

Regards
Haojian
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