[PATCH 0/2] fbdev: Adjustments for fb_alloc_cmap_gfp()

[PATCH 0/2] fbdev: Adjustments for fb_alloc_cmap_gfp()

[Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Tue, 23 May 2023 22:04:33 +0200

A few update suggestions were taken into account
from static source code analysis.

Markus Elfring (2):
  Move two variable assignments
  Convert a variable initialisation into a later assignment

 drivers/video/fbdev/core/fbcmap.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--
2.40.1

[PATCH 1/2] fbdev: Move two variable assignments in fb_alloc_cmap_gfp()

[Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Tue, 23 May 2023 21:30:29 +0200

Move the assignment for the local variables “size” and “flags”
because the computed values were only used in a single if branch.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/video/fbdev/core/fbcmap.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcmap.c b/drivers/video/fbdev/core/fbcmap.c
index ff09e57f3c38..5c1075ed28ab 100644
--- a/drivers/video/fbdev/core/fbcmap.c
+++ b/drivers/video/fbdev/core/fbcmap.c
@@ -91,16 +91,17 @@ static const struct fb_cmap default_16_colors = {

 int fb_alloc_cmap_gfp(struct fb_cmap *cmap, int len, int transp, gfp_t flags)
 {
-	int size = len * sizeof(u16);
 	int ret = -ENOMEM;

-	flags |= __GFP_NOWARN;
-
 	if (cmap->len != len) {
+		int size;
+
 		fb_dealloc_cmap(cmap);
 		if (!len)
 			return 0;

+		size = len * sizeof(u16);
+		flags |= __GFP_NOWARN;
 		cmap->red = kzalloc(size, flags);
 		if (!cmap->red)
 			goto fail;
--
2.40.1

[PATCH 2/2] fbdev: Convert a variable initialisation into a later assignment in fb_alloc_cmap_gfp()

[Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Tue, 23 May 2023 21:56:55 +0200

* Assign the value “-ENOMEM” to the local variable “ret” only for
  the exception handling.

* Use an additional label.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/video/fbdev/core/fbcmap.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcmap.c b/drivers/video/fbdev/core/fbcmap.c
index 5c1075ed28ab..fbe82a64cf73 100644
--- a/drivers/video/fbdev/core/fbcmap.c
+++ b/drivers/video/fbdev/core/fbcmap.c
@@ -91,7 +91,7 @@ static const struct fb_cmap default_16_colors = {

 int fb_alloc_cmap_gfp(struct fb_cmap *cmap, int len, int transp, gfp_t flags)
 {
-	int ret = -ENOMEM;
+	int ret;

 	if (cmap->len != len) {
 		int size;
@@ -104,17 +104,20 @@ int fb_alloc_cmap_gfp(struct fb_cmap *cmap, int len, int transp, gfp_t flags)
 		flags |= __GFP_NOWARN;
 		cmap->red = kzalloc(size, flags);
 		if (!cmap->red)
-			goto fail;
+			goto e_nomem;
+
 		cmap->green = kzalloc(size, flags);
 		if (!cmap->green)
-			goto fail;
+			goto e_nomem;
+
 		cmap->blue = kzalloc(size, flags);
 		if (!cmap->blue)
-			goto fail;
+			goto e_nomem;
+
 		if (transp) {
 			cmap->transp = kzalloc(size, flags);
 			if (!cmap->transp)
-				goto fail;
+				goto e_nomem;
 		} else {
 			cmap->transp = NULL;
 		}
@@ -126,6 +129,8 @@ int fb_alloc_cmap_gfp(struct fb_cmap *cmap, int len, int transp, gfp_t flags)
 		goto fail;
 	return 0;

+e_nomem:
+	ret = -ENOMEM;
 fail:
 	fb_dealloc_cmap(cmap);
 	return ret;
--
2.40.1

Re: [PATCH 1/2] fbdev: Move two variable assignments in fb_alloc_cmap_gfp()

[Helge Deller]

On 5/23/23 22:15, Markus Elfring wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Tue, 23 May 2023 21:30:29 +0200
>
> Move the assignment for the local variables “size” and “flags”
> because the computed values were only used in a single if branch.

Please do not move such variables without real need.
It makes backporting (of this and maybe follow-up patches) much more
complicated and the compiler will optimize it anyway.

Thanks!
Helge


> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>   drivers/video/fbdev/core/fbcmap.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/video/fbdev/core/fbcmap.c b/drivers/video/fbdev/core/fbcmap.c
> index ff09e57f3c38..5c1075ed28ab 100644
> --- a/drivers/video/fbdev/core/fbcmap.c
> +++ b/drivers/video/fbdev/core/fbcmap.c
> @@ -91,16 +91,17 @@ static const struct fb_cmap default_16_colors = {
>
>   int fb_alloc_cmap_gfp(struct fb_cmap *cmap, int len, int transp, gfp_t flags)
>   {
> -	int size = len * sizeof(u16);
>   	int ret = -ENOMEM;
>
> -	flags |= __GFP_NOWARN;
> -
>   	if (cmap->len != len) {
> +		int size;
> +
>   		fb_dealloc_cmap(cmap);
>   		if (!len)
>   			return 0;
>
> +		size = len * sizeof(u16);
> +		flags |= __GFP_NOWARN;
>   		cmap->red = kzalloc(size, flags);
>   		if (!cmap->red)
>   			goto fail;
> --
> 2.40.1
>

Re: [PATCH 1/2] fbdev: Move two variable assignments in fb_alloc_cmap_gfp()

[Markus Elfring]

>> Move the assignment for the local variables “size” and “flags”
>> because the computed values were only used in a single if branch.
>
> Please do not move such variables without real need.

Is there a need to explain desirable effects better?


> It makes backporting (of this and maybe follow-up patches) much more complicated

I suggest to reconsider such development concerns a bit more.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/drivers/video/fbdev/core/fbcmap.c?h=v6.4-rc3


> and the compiler will optimize it anyway.

How much do expectations fit to supported and documented software optimisations?

Regards,
Markus