linux-kernel - Re: [PATCH v2 2/2] drm/i915/fbc: Avoid full proxy f

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Message-ID: <Y77P3Qt7P9BRMlco@ubun2204.myguest.virtualbox.org>
Date:   Wed, 11 Jan 2023 20:33:57 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>,
        Saurabh Singh Sengar <ssengar@...rosoft.com>
Subject: Re: [PATCH v2 2/2] drm/i915/fbc: Avoid full proxy f_ops for FBC
 debug attributes

On Tue, Jan 10, 2023 at 01:52:05PM -0500, Rodrigo Vivi wrote:
> On Tue, Jan 10, 2023 at 11:45:40PM +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>
> 
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@...el.com>
> 
> (Are you planning to send the one for pxp file?)

Hello Rodrigo,
The pxp file is implemented differently using a common function for another SHOW
attribute file. I am exploring how to best handle that and would send in a patch
if feasible. See the simplified code snip below:

	static const struct intel_gt_debugfs_file files[] = {
		{ "info", &pxp_info_fops, NULL },
		{ "terminate_state", &pxp_terminate_fops, NULL },
	};
	...
	intel_gt_debugfs_register_files(root, files, ARRAY_SIZE(files), pxp);

Thank you.
./drv

> 
> > ---
> > Changes in v2:
> >    - Include coccicheck make command in the patch log message for clarity.
> >      Suggested by Rodrigo Vivi <rodrigo.vivi@...el.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 5e69d3c11d21..c508dcf415b4 100644
> > --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> > +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> > @@ -1807,10 +1807,10 @@ 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)
> > @@ -1819,8 +1819,8 @@ 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
> > 
> > 
> >