[PATCH] drm/i915/fbc: Avoid full proxy f_ops for FBC debug attributes

[Rodrigo Vivi]

On Tue, Dec 27, 2022 at 01:30:53PM +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.
> 
> This Change is reported by the debugfs_simple_attr.cocci Coccinelle
> semantic patch.

I just checked here with
$ make coccicheck M=drivers/gpu/drm/i915/ MODE=context COCCI=./scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci

The part reported by the this script is the s/SIMPLE/DEBUGFS
but the change to the unsafe option is not.

This commit message is not explaining why the unsafe is the suggested
or who suggested it.

If you remove the unsafe part feel free to resend adding:

Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
(to both patches, this and the drrs one.

Also, it looks like you could contribute with other 2 patches:
drivers/gpu/drm/i915/pxp/intel_pxp_debugfs.c:64:0-23: WARNING: pxp_terminate_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE
drivers/gpu/drm/i915/gvt/debugfs.c:150:0-23: WARNING: vgpu_scan_nonprivbb_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE

> 
> Signed-off-by: Deepak R Varma <drv at mailo.com>
> ---
>  drivers/gpu/drm/i915/display/intel_fbc.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> index b5ee5ea0d010..4b481e2f908b 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> @@ -1809,10 +1809,10 @@ static int intel_fbc_debugfs_false_color_set(void *data, u64 val)
>  	return 0;
>  }
> 
> -DEFINE_SIMPLE_ATTRIBUTE(intel_fbc_debugfs_false_color_fops,
> -			intel_fbc_debugfs_false_color_get,
> -			intel_fbc_debugfs_false_color_set,
> -			"%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(intel_fbc_debugfs_false_color_fops,
> +			 intel_fbc_debugfs_false_color_get,
> +			 intel_fbc_debugfs_false_color_set,
> +			 "%llu\n");
> 
>  static void intel_fbc_debugfs_add(struct intel_fbc *fbc,
>  				  struct dentry *parent)
> @@ -1821,8 +1821,8 @@ static void intel_fbc_debugfs_add(struct intel_fbc *fbc,
>  			    fbc, &intel_fbc_debugfs_status_fops);
> 
>  	if (fbc->funcs->set_false_color)
> -		debugfs_create_file("i915_fbc_false_color", 0644, parent,
> -				    fbc, &intel_fbc_debugfs_false_color_fops);
> +		debugfs_create_file_unsafe("i915_fbc_false_color", 0644, parent,
> +					   fbc, &intel_fbc_debugfs_false_color_fops);
>  }
> 
>  void intel_fbc_crtc_debugfs_add(struct intel_crtc *crtc)
> --
> 2.34.1
> 
> 
>