[PATCH] drm/panel: st7703: Avoid full proxy f_ops for st7703 debug attributes

[PATCH] drm/panel: st7703: Avoid full proxy f_ops for st7703 debug attributes

[Deepak R Varma]

Using DEFINE_SIMPLE_ATTRIBUTE macro with the debugfs_create_file()
function adds the overhead of introducing a proxy file operation
functions to wrap the original read/write inside file removal protection
functions. This adds significant overhead in terms of introducing and
managing the proxy factory file operations structure and function
wrapping at runtime.
As a replacement, a combination of DEFINE_DEBUGFS_ATTRIBUTE macro paired
with debugfs_create_file_unsafe() is suggested to be used instead.  The
DEFINE_DEBUGFS_ATTRIBUTE utilises debugfs_file_get() and
debugfs_file_put() wrappers to protect the original read and write
function calls for the debug attributes. There is no need for any
runtime proxy file operations to be managed by the debugfs core.
Following coccicheck make command helped identify this change:

make coccicheck M=drivers/gpu/drm/i915/ MODE=patch COCCI=./scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci

Signed-off-by: Deepak R Varma <drv@mailo.com>
---
Note: Patch compile tested only.

 drivers/gpu/drm/panel/panel-sitronix-st7703.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-sitronix-st7703.c b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
index 86a472b01360..22ed7e2b0e00 100644
--- a/drivers/gpu/drm/panel/panel-sitronix-st7703.c
+++ b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
@@ -510,15 +510,14 @@ static int allpixelson_set(void *data, u64 val)
 	return 0;
 }
 
-DEFINE_SIMPLE_ATTRIBUTE(allpixelson_fops, NULL,
-			allpixelson_set, "%llu\n");
+DEFINE_DEBUGFS_ATTRIBUTE(allpixelson_fops, NULL, allpixelson_set, "%llu\n");
 
 static void st7703_debugfs_init(struct st7703 *ctx)
 {
 	ctx->debugfs = debugfs_create_dir(DRV_NAME, NULL);
 
-	debugfs_create_file("allpixelson", 0600, ctx->debugfs, ctx,
-			    &allpixelson_fops);
+	debugfs_create_file_unsafe("allpixelson", 0600, ctx->debugfs, ctx,
+				   &allpixelson_fops);
 }
 
 static void st7703_debugfs_remove(struct st7703 *ctx)
-- 
2.34.1

Re: [PATCH] drm/panel: st7703: Avoid full proxy f_ops for st7703 debug attributes

[Sam Ravnborg]

On Wed, Jan 11, 2023 at 01:53:34AM +0530, Deepak R Varma wrote:
> Using DEFINE_SIMPLE_ATTRIBUTE macro with the debugfs_create_file()
> function adds the overhead of introducing a proxy file operation
> functions to wrap the original read/write inside file removal protection
> functions. This adds significant overhead in terms of introducing and
> managing the proxy factory file operations structure and function
> wrapping at runtime.
> As a replacement, a combination of DEFINE_DEBUGFS_ATTRIBUTE macro paired
> with debugfs_create_file_unsafe() is suggested to be used instead.  The
> DEFINE_DEBUGFS_ATTRIBUTE utilises debugfs_file_get() and
> debugfs_file_put() wrappers to protect the original read and write
> function calls for the debug attributes. There is no need for any
> runtime proxy file operations to be managed by the debugfs core.
> Following coccicheck make command helped identify this change:
> 
> make coccicheck M=drivers/gpu/drm/i915/ MODE=patch COCCI=./scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
> 
> Signed-off-by: Deepak R Varma <drv@mailo.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>

Anyone up for testing this change?
I have never dealt with debugfs so dunno if the chnage will work or not.

	Sam

> ---
> Note: Patch compile tested only.
> 
>  drivers/gpu/drm/panel/panel-sitronix-st7703.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-sitronix-st7703.c b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> index 86a472b01360..22ed7e2b0e00 100644
> --- a/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> +++ b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> @@ -510,15 +510,14 @@ static int allpixelson_set(void *data, u64 val)
>  	return 0;
>  }
>  
> -DEFINE_SIMPLE_ATTRIBUTE(allpixelson_fops, NULL,
> -			allpixelson_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(allpixelson_fops, NULL, allpixelson_set, "%llu\n");
>  
>  static void st7703_debugfs_init(struct st7703 *ctx)
>  {
>  	ctx->debugfs = debugfs_create_dir(DRV_NAME, NULL);
>  
> -	debugfs_create_file("allpixelson", 0600, ctx->debugfs, ctx,
> -			    &allpixelson_fops);
> +	debugfs_create_file_unsafe("allpixelson", 0600, ctx->debugfs, ctx,
> +				   &allpixelson_fops);
>  }
>  
>  static void st7703_debugfs_remove(struct st7703 *ctx)
> -- 
> 2.34.1
> 
>