linux-kernel - Re: [PATCH] drm/panel: st7703: Avoid full proxy f

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Message-ID: <Y8F2AQdzVEdmeWGU@ravnborg.org>
Date:   Fri, 13 Jan 2023 16:17:21 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Deepak R Varma <drv@...lo.com>
Cc:     Guido Günther <agx@...xcpu.org>,
        Purism Kernel Team <kernel@...i.sm>,
        Ondrej Jirman <megous@...ous.com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>
Subject: Re: [PATCH] drm/panel: st7703: Avoid full proxy f_ops for st7703
 debug attributes

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@...lo.com>
Acked-by: Sam Ravnborg <sam@...nborg.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
> 
>