[PATCH] of/platform: Avoid compilation warning

[PATCH] of/platform: Avoid compilation warning

[Miquel Raynal]

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:

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@bootlin.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

Re: [PATCH] of/platform: Avoid compilation warning

[Rob Herring]

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@bootlin.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
> 

Re: [PATCH] of/platform: Avoid compilation warning

[Miquel Raynal]

Hi Rob,

Rob Herring <robh@kernel.org> wrote on Wed, 27 May 2020 12:35:55 -0600:

> 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. 

Ok, makes sense. Perhaps we should entirely get rid of it, I don't see
a lot of users left. Or at least update the comment I was mentioning.

Cheers,
Miquèl