[PATCH] powermac: Call of_node_put(bk_node) only once in pmac_has_backlight_type()

[PATCH] powermac: Call of_node_put(bk_node) only once in pmac_has_backlight_type()

[Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Wed, 2 Oct 2024 21:50:27 +0200

An of_node_put(bk_node) call was immediately used after a pointer check
for an of_get_property() call in this function implementation.
Thus call such a function only once instead directly before the check.

This issue was transformed by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 arch/powerpc/platforms/powermac/backlight.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/platforms/powermac/backlight.c b/arch/powerpc/platforms/powermac/backlight.c
index 12bc01353bd3..d3666595a62e 100644
--- a/arch/powerpc/platforms/powermac/backlight.c
+++ b/arch/powerpc/platforms/powermac/backlight.c
@@ -61,11 +61,9 @@ int pmac_has_backlight_type(const char *type)
 	if (bk_node) {
 		const char *prop = of_get_property(bk_node,
 				"backlight-control", NULL);
-		if (prop && strncmp(prop, type, strlen(type)) == 0) {
-			of_node_put(bk_node);
-			return 1;
-		}
 		of_node_put(bk_node);
+		if (prop && strncmp(prop, type, strlen(type)) == 0)
+			return 1;
 	}

 	return 0;
--
2.46.1

Re: [PATCH] powermac: Call of_node_put(bk_node) only once in pmac_has_backlight_type()

[Christophe Leroy]

Le 02/10/2024 à 22:02, Markus Elfring a écrit :
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Wed, 2 Oct 2024 21:50:27 +0200
> 
> An of_node_put(bk_node) call was immediately used after a pointer check
> for an of_get_property() call in this function implementation.
> Thus call such a function only once instead directly before the check.

It seems pointless to perform a put immediately after a get. Shouldn't 
of_find_property() be used instead ? And then of_property_read_string() 
would probably be better.

Maybe you can even use of_property_match_string().

> 
> This issue was transformed by using the Coccinelle software.
> 
> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>   arch/powerpc/platforms/powermac/backlight.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powermac/backlight.c b/arch/powerpc/platforms/powermac/backlight.c
> index 12bc01353bd3..d3666595a62e 100644
> --- a/arch/powerpc/platforms/powermac/backlight.c
> +++ b/arch/powerpc/platforms/powermac/backlight.c
> @@ -61,11 +61,9 @@ int pmac_has_backlight_type(const char *type)
>   	if (bk_node) {
>   		const char *prop = of_get_property(bk_node,
>   				"backlight-control", NULL);
> -		if (prop && strncmp(prop, type, strlen(type)) == 0) {
> -			of_node_put(bk_node);
> -			return 1;
> -		}
>   		of_node_put(bk_node);
> +		if (prop && strncmp(prop, type, strlen(type)) == 0)
> +			return 1;
>   	}
> 
>   	return 0;
> --
> 2.46.1
> 

Re: [PATCH] powermac: Call of_node_put(bk_node) only once in pmac_has_backlight_type()

[Dan Carpenter]

First of all, the change is wrong.  We can't dereference "prop" after calling
of_node_put().  You have to be a bit extra careful reviewing Markus's patches
because a lot of the rest of us have blocked these messages so you're on your
own in that way.

On Wed, Oct 02, 2024 at 10:43:46PM +0200, Christophe Leroy wrote:
> 
> 
> Le 02/10/2024 à 22:02, Markus Elfring a écrit :
> > From: Markus Elfring <elfring@users.sourceforge.net>
> > Date: Wed, 2 Oct 2024 21:50:27 +0200
> > 
> > An of_node_put(bk_node) call was immediately used after a pointer check
> > for an of_get_property() call in this function implementation.
> > Thus call such a function only once instead directly before the check.
> 
> It seems pointless to perform a put immediately after a get. Shouldn't
> of_find_property() be used instead ? And then of_property_read_string()
> would probably be better.
> 
> Maybe you can even use of_property_match_string().

The of_get_property() function doesn't do a get as in get/put, it just finds
the property and returns it.  It doesn't bump the reference count.  It's a
confusing name in that way.  The The of_node_put() pairs with
of_find_node_by_name().

regards,
dan carpenter

Re: [PATCH] powermac: Call of_node_put(bk_node) only once in pmac_has_backlight_type()

[Krzysztof Kozlowski]

On 03/10/2024 07:56, Dan Carpenter wrote:
> First of all, the change is wrong.  We can't dereference "prop" after calling
> of_node_put().  You have to be a bit extra careful reviewing Markus's patches
> because a lot of the rest of us have blocked these messages so you're on your
> own in that way.

Yep, I plonked him some time ago and everything is in spam.

The code looks just incorrect and I think Markus did not understand it
before transforming.

Best regards,
Krzysztof

Re: powermac: Call of_node_put(bk_node) only once in pmac_has_backlight_type()

[Markus Elfring]

> First of all, the change is wrong.  We can't dereference "prop" after calling
> of_node_put().
…
> The of_get_property() function doesn't do a get as in get/put, it just finds
> the property and returns it.  It doesn't bump the reference count.  It's a
> confusing name in that way.  The The of_node_put() pairs with
> of_find_node_by_name().
Thanks for your information.

* Do you see opportunities for improving the software documentation accordingly?

* How much can source code analysis tools influence development efforts?


Regards,
Markus

Re: [PATCH] powermac: Call of_node_put(bk_node) only once in pmac_has_backlight_type()

[Michael Ellerman]

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Le 02/10/2024 à 22:02, Markus Elfring a écrit :
>> From: Markus Elfring <elfring@users.sourceforge.net>
>> Date: Wed, 2 Oct 2024 21:50:27 +0200
>> 
>> An of_node_put(bk_node) call was immediately used after a pointer check
>> for an of_get_property() call in this function implementation.
>> Thus call such a function only once instead directly before the check.
>
> It seems pointless to perform a put immediately after a get. Shouldn't 
> of_find_property() be used instead ? And then of_property_read_string() 
> would probably be better.
>
> Maybe you can even use of_property_match_string().

Yes that would clean it up nicely I think, eg:

int pmac_has_backlight_type(const char *type)
{
        struct device_node* bk_node = of_find_node_by_name(NULL, "backlight");
        int i;

        i = of_property_match_string(bk_node, "backlight-control", type);
        of_node_put(bk_node);

        return i >= 0;
}

cheers

[PATCH] powermac: Use of_property_match_string() in pmac_has_backlight_type()

[Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Fri, 11 Oct 2024 18:10:06 +0200

Replace an of_get_property() call by of_property_match_string()
so that this function implementation can be simplified.

Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/linuxppc-dev/d9bdc1b6-ea7e-47aa-80aa-02ae649abf72@csgroup.eu/
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/linuxppc-dev/87cyk97ufp.fsf@mail.lhotse/
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 arch/powerpc/platforms/powermac/backlight.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/platforms/powermac/backlight.c b/arch/powerpc/platforms/powermac/backlight.c
index 12bc01353bd3..79741370c40c 100644
--- a/arch/powerpc/platforms/powermac/backlight.c
+++ b/arch/powerpc/platforms/powermac/backlight.c
@@ -57,18 +57,10 @@ struct backlight_device *pmac_backlight;
 int pmac_has_backlight_type(const char *type)
 {
 	struct device_node* bk_node = of_find_node_by_name(NULL, "backlight");
+	int i = of_property_match_string(bk_node, "backlight-control", type);

-	if (bk_node) {
-		const char *prop = of_get_property(bk_node,
-				"backlight-control", NULL);
-		if (prop && strncmp(prop, type, strlen(type)) == 0) {
-			of_node_put(bk_node);
-			return 1;
-		}
-		of_node_put(bk_node);
-	}
-
-	return 0;
+	of_node_put(bk_node);
+	return i >= 0;
 }

 static void pmac_backlight_key_worker(struct work_struct *work)
--
2.46.1

Re: [PATCH] powermac: Use of_property_match_string() in pmac_has_backlight_type()

[Christophe Leroy]

Le 11/10/2024 à 18:18, Markus Elfring a écrit :
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Fri, 11 Oct 2024 18:10:06 +0200
> 
> Replace an of_get_property() call by of_property_match_string()
> so that this function implementation can be simplified.
> 
> Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Link: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flinuxppc-dev%2Fd9bdc1b6-ea7e-47aa-80aa-02ae649abf72%40csgroup.eu%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cf278e44683c04b931b9c08dcea106447%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638642603333398766%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=6byvgvuGiBSVu8F6kLA2OozUuHZunJRH%2BU%2Bq9q7osmM%3D&reserved=0
> Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
> Link: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flinuxppc-dev%2F87cyk97ufp.fsf%40mail.lhotse%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cf278e44683c04b931b9c08dcea106447%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638642603333422636%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=IDuYfe3UoaIEmedJ07H67zvzrPnzbQ2g8EeTtbJ%2BbZ8%3D&reserved=0
> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>   arch/powerpc/platforms/powermac/backlight.c | 14 +++-----------
>   1 file changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powermac/backlight.c b/arch/powerpc/platforms/powermac/backlight.c
> index 12bc01353bd3..79741370c40c 100644
> --- a/arch/powerpc/platforms/powermac/backlight.c
> +++ b/arch/powerpc/platforms/powermac/backlight.c
> @@ -57,18 +57,10 @@ struct backlight_device *pmac_backlight;
>   int pmac_has_backlight_type(const char *type)
>   {
>   	struct device_node* bk_node = of_find_node_by_name(NULL, "backlight");
> +	int i = of_property_match_string(bk_node, "backlight-control", type);
> 
> -	if (bk_node) {
> -		const char *prop = of_get_property(bk_node,
> -				"backlight-control", NULL);
> -		if (prop && strncmp(prop, type, strlen(type)) == 0) {
> -			of_node_put(bk_node);
> -			return 1;
> -		}
> -		of_node_put(bk_node);
> -	}
> -
> -	return 0;
> +	of_node_put(bk_node);
> +	return i >= 0;

Could have been:

	return !IS_ERR_VALUE(i);


Never mind,

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>

>   }
> 
>   static void pmac_backlight_key_worker(struct work_struct *work)
> --
> 2.46.1
> 

Re: [PATCH] powermac: Use of_property_match_string() in pmac_has_backlight_type()

[Dan Carpenter]

On Fri, Oct 11, 2024 at 06:25:45PM +0200, Christophe Leroy wrote:
> > diff --git a/arch/powerpc/platforms/powermac/backlight.c b/arch/powerpc/platforms/powermac/backlight.c
> > index 12bc01353bd3..79741370c40c 100644
> > --- a/arch/powerpc/platforms/powermac/backlight.c
> > +++ b/arch/powerpc/platforms/powermac/backlight.c
> > @@ -57,18 +57,10 @@ struct backlight_device *pmac_backlight;
> >   int pmac_has_backlight_type(const char *type)
> >   {
> >   	struct device_node* bk_node = of_find_node_by_name(NULL, "backlight");
> > +	int i = of_property_match_string(bk_node, "backlight-control", type);
> > 
> > -	if (bk_node) {
> > -		const char *prop = of_get_property(bk_node,
> > -				"backlight-control", NULL);
> > -		if (prop && strncmp(prop, type, strlen(type)) == 0) {
> > -			of_node_put(bk_node);
> > -			return 1;
> > -		}
> > -		of_node_put(bk_node);
> > -	}
> > -
> > -	return 0;
> > +	of_node_put(bk_node);
> > +	return i >= 0;
> 
> Could have been:
> 
> 	return !IS_ERR_VALUE(i);
> 

IS_ERR_VALUE() macro should only be used when you're dealing with memory
addresses.  What I mean is there places in mm/ where we pass addresses as
unsigned long values instead of pointers.  For example, get_unmapped_area()
returns unsigned long.  The IS_ERR_VALUE() macro is necessary for that.

For regular error codes, we can just check for negatives.  we don't have do
anything fancy.

Of course, you can find counter examples, like msm_iommu_attach_dev() or
st_fdma_of_xlate().  <small joke>But in those cases, it's done to deliberately
to ensure that the code will never accidentally get built on 64bit systems.
</small joke>

regards,
dan carpenter

Re: [PATCH] powermac: Use of_property_match_string() in pmac_has_backlight_type()

[Michael Ellerman]

On Fri, 11 Oct 2024 18:18:42 +0200, Markus Elfring wrote:
> Replace an of_get_property() call by of_property_match_string()
> so that this function implementation can be simplified.
> 
> 

Applied to powerpc/next.

[1/1] powermac: Use of_property_match_string() in pmac_has_backlight_type()
      https://git.kernel.org/powerpc/c/2e716f5cdebed2fb98cafffaf626645c2e922dbb

cheers