linux-kernel - Re: [PATCH] of/platform: Avoid compilation warning

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Date:   Wed, 27 May 2020 12:35:55 -0600
From:   Rob Herring <robh@...nel.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of/platform: Avoid compilation warning

On Thu, May 14, 2020 at 07:07:07PM +0200, Miquel Raynal wrote:
> The of_find_device_by_node() helper has its dummy counterpart for when
> CONFIG_OF is not enabled. However, it is clearly stated in the kernel
> documentation that it "takes a reference to the embedded struct device
> which needs to be dropped after use". Which means the of_dev_put()
> helper might have to be called afterwards. Unfortunately, there is no
> of_dev_put() dummy function if OF_CONFIG is not enabled which seems
> odd in this case. The of_dev_put() helper is pretty simple, it just
> checks the validity of the single argument and calls put_device() on
> it. One can just call put_device() directly to avoid any build issue
> but I find much more accurate in this case to create the dummy
> helper.
> 
> With this helper, a file using of_find_device_by_node() can also call
> of_dev_put() without triggering the following:

IMO, you should use platform_device_put() instead. It has the NULL check 
too.

I imagine of_dev_put() is left over from when OF devices were not 
platform devices. 
 
> error: implicit declaration of function ‘of_dev_put’; did you mean ‘of_node_put’? [-Werror=implicit-function-declaration]
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
>  include/linux/of_platform.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/of_platform.h b/include/linux/of_platform.h
> index 84a966623e78..84d9e60e517e 100644
> --- a/include/linux/of_platform.h
> +++ b/include/linux/of_platform.h
> @@ -54,11 +54,13 @@ extern struct platform_device *of_device_alloc(struct device_node *np,
>  					 struct device *parent);
>  #ifdef CONFIG_OF
>  extern struct platform_device *of_find_device_by_node(struct device_node *np);
> +extern void of_dev_put(struct platform_device *dev);
>  #else
>  static inline struct platform_device *of_find_device_by_node(struct device_node *np)
>  {
>  	return NULL;
>  }
> +static inline void of_dev_put(struct platform_device *dev) { }
>  #endif
>  
>  /* Platform devices and busses creation */
> -- 
> 2.20.1
>