Re: [PATCH 4/4] vgaswitcheroo: do not check for NULL debugfs dentry

[Lukas Wunner <lukas@wunner.de>]

On Mon, Oct 11, 2021 at 09:06:07PM +0200, Nirmoy Das wrote:
> Debugfs APIs returns encoded error on failure so use
> debugfs_lookup() instead of checking for NULL.
[...]
> --- a/drivers/gpu/vga/vga_switcheroo.c
> +++ b/drivers/gpu/vga/vga_switcheroo.c
> @@ -914,7 +914,7 @@ static void vga_switcheroo_debugfs_fini(struct vgasr_priv *priv)
>  static void vga_switcheroo_debugfs_init(struct vgasr_priv *priv)
>  {
>  	/* already initialised */
> -	if (priv->debugfs_root)
> +	if (debugfs_lookup("vgaswitcheroo", NULL))
>  		return;
> 
>  	priv->debugfs_root = debugfs_create_dir("vgaswitcheroo", NULL);

If debugfs_create_dir() returns an error code, it does make sense to
retry the call when another vga_switcheroo client registers later.
I like that.

However I'd prefer simply changing this to explicitly check for NULL, i.e.:

-	if (priv->debugfs_root)
+	if (priv->debugfs_root == NULL)

It's just as clear as calling debugfs_lookup() and it has way less
overhead.  Granted, this isn't a hot path, but it's called on boot,
and the less code we execute, the faster the machine boots.

Thanks,

Lukas