[PATCH 1/7] Make for_each_child_of_node() reference its args when CONFIG_OF=n

[PATCH 1/7] Make for_each_child_of_node() reference its args when CONFIG_OF=n

[David Howells]

Make for_each_child_of_node() reference its args when CONFIG_OF=n to avoid
warnings like:

	drivers/leds/leds-pwm.c:88:22: warning: unused variable 'node' [-Wunused-variable]
	  struct device_node *node = pdev->dev.of_node;
			      ^

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Grant Likely <grant.likely@linaro.org>
cc: Rob Herring <robh+dt@kernel.org>
cc: devicetree@vger.kernel.org
---

 include/linux/of.h |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/of.h b/include/linux/of.h
index 276c546980d8..70c64ba17fa5 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -377,8 +377,13 @@ static inline bool of_have_populated_dt(void)
 	return false;
 }
 
+/* Kill an unused variable warning on a device_node pointer */
+static inline void __of_use_dn(const struct device_node *np)
+{
+}
+
 #define for_each_child_of_node(parent, child) \
-	while (0)
+	while (__of_use_dn(parent), __of_use_dn(child), 0)
 
 #define for_each_available_child_of_node(parent, child) \
 	while (0)

Re: [PATCH 1/7] Make for_each_child_of_node() reference its args when CONFIG_OF=n

[Andrew Morton]

> Subject: [PATCH 1/7] Make for_each_child_of_node() reference its args when CONFIG_OF=n

Nit: Documentation/SubmittingPatches, section 15.  "subsystem: " is
missing from all patche titles.

On Fri, 03 Jan 2014 16:07:23 +0000 David Howells <dhowells@redhat.com> wrote:

> Make for_each_child_of_node() reference its args when CONFIG_OF=n to avoid
> warnings like:
> 
> 	drivers/leds/leds-pwm.c:88:22: warning: unused variable 'node' [-Wunused-variable]
> 	  struct device_node *node = pdev->dev.of_node;
> 			      ^
> ...
>
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -377,8 +377,13 @@ static inline bool of_have_populated_dt(void)
>  	return false;
>  }
>  
> +/* Kill an unused variable warning on a device_node pointer */
> +static inline void __of_use_dn(const struct device_node *np)
> +{
> +}
> +
>  #define for_each_child_of_node(parent, child) \
> -	while (0)
> +	while (__of_use_dn(parent), __of_use_dn(child), 0)
>  
>  #define for_each_available_child_of_node(parent, child) \
>  	while (0)

That's a bit ugly.  __maybe_unused fixes it appropriately but can't be
placed into the macro.


I wonder if we should instead generalise it to

static inline void reference_var_to_squish_gcc_warning(const void *p)
{
}

I guess not, until/unless we find other macros which need the same
treatment.


Yes, passing a var to an empty function suppresses the warning.  But is
this intentional or a happy accident?  Future gcc's could quite
legitimately be enhanced to detect that the arg is still unused and
then we'd need to find a new way of suppressing the warning, if such
exists.