Re: [PATCH v3 2/5] drm/plane: Expose function to create format/modifier blob

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Jan 27, 2025 at 07:25:31AM +0000, Borah, Chaitanya Kumar wrote:
> Hello Ville,
> 
> > -----Original Message-----
> > From: Intel-xe <intel-xe-bounces@lists.freedesktop.org> On Behalf Of Murthy,
> > Arun R
> > Sent: Saturday, January 25, 2025 12:25 PM
> > To: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: dri-devel@lists.freedesktop.org; intel-gfx@lists.freedesktop.org; intel-
> > xe@lists.freedesktop.org
> > Subject: RE: [PATCH v3 2/5] drm/plane: Expose function to create
> > format/modifier blob
> > 
> > > On Thu, Jan 23, 2025 at 07:47:14AM +0000, Murthy, Arun R wrote:
> > > > > > On Wed, Jan 08, 2025 at 11:09:00AM +0530, Arun R Murthy wrote:
> > > > > > > Expose drm plane function to create formats/modifiers blob.
> > > > > > > This function can be used to expose list of supported
> > > > > > > formats/modifiers for sync/async flips.
> > > > > > >
> > > > > > > Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> > > > > > > ---
> > > > > > >  drivers/gpu/drm/drm_plane.c | 44
> > > > > > > +++++++++++++++++++++++++++++-------
> > > > > > --------
> > > > > > >  include/drm/drm_plane.h     |  4 ++++
> > > > > > >  2 files changed, 33 insertions(+), 15 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/gpu/drm/drm_plane.c
> > > > > > > b/drivers/gpu/drm/drm_plane.c index
> > > > > > >
> > > > > >
> > > > >
> > >
> > 416818e54ccffcf3d3aada2723e96ce8ccf1dd97..4f35eec2b7770fcc90c3e07a90
> > > > > 6
> > > > > > 8
> > > > > > > b31c0563a4c0 100644
> > > > > > > --- a/drivers/gpu/drm/drm_plane.c
> > > > > > > +++ b/drivers/gpu/drm/drm_plane.c
> > > > > > > @@ -191,7 +191,10 @@ modifiers_ptr(struct
> > > > > > > drm_format_modifier_blob
> > > > > > *blob)
> > > > > > >  	return (struct drm_format_modifier *)(((char *)blob) +
> > > > > > > blob->modifiers_offset);  }
> > > > > > >
> > > > > > > -static int create_in_format_blob(struct drm_device *dev,
> > > > > > > struct drm_plane *plane)
> > > > > > > +int drm_plane_create_format_blob(struct drm_device *dev,
> > > > > > > +				 struct drm_plane *plane, u64
> > > *modifiers,
> > > > > > > +				 unsigned int modifier_count, u32
> > > *formats,
> > > > > > > +				 unsigned int format_count, bool
> > > is_async)
> > > > > > >  {
> > > > > > >  	const struct drm_mode_config *config = &dev->mode_config;
> > > > > > >  	struct drm_property_blob *blob; @@ -200,14 +203,14 @@
> > static
> > > > > > > int create_in_format_blob(struct drm_device
> > > > > > *dev, struct drm_plane *plane
> > > > > > >  	struct drm_format_modifier_blob *blob_data;
> > > > > > >  	unsigned int i, j;
> > > > > > >
> > > > > > > -	formats_size = sizeof(__u32) * plane->format_count;
> > > > > > > +	formats_size = sizeof(__u32) * format_count;
> > > > > > >  	if (WARN_ON(!formats_size)) {
> > > > > > >  		/* 0 formats are never expected */
> > > > > > >  		return 0;
> > > > > > >  	}
> > > > > > >
> > > > > > >  	modifiers_size =
> > > > > > > -		sizeof(struct drm_format_modifier) * plane-
> > >modifier_count;
> > > > > > > +		sizeof(struct drm_format_modifier) * modifier_count;
> > > > > > >
> > > > > > >  	blob_size = sizeof(struct drm_format_modifier_blob);
> > > > > > >  	/* Modifiers offset is a pointer to a struct with a 64 bit
> > > > > > > field so it @@ -223,37 +226,45 @@ static int
> > > > > > > create_in_format_blob(struct drm_device *dev, struct drm_plane
> > > > > > > *plane
> > > > > > >
> > > > > > >  	blob_data = blob->data;
> > > > > > >  	blob_data->version = FORMAT_BLOB_CURRENT;
> > > > > > > -	blob_data->count_formats = plane->format_count;
> > > > > > > +	blob_data->count_formats = format_count;
> > > > > > >  	blob_data->formats_offset = sizeof(struct
> > drm_format_modifier_blob);
> > > > > > > -	blob_data->count_modifiers = plane->modifier_count;
> > > > > > > +	blob_data->count_modifiers = modifier_count;
> > > > > > >
> > > > > > >  	blob_data->modifiers_offset =
> > > > > > >  		ALIGN(blob_data->formats_offset + formats_size, 8);
> > > > > > >
> > > > > > > -	memcpy(formats_ptr(blob_data), plane->format_types,
> > formats_size);
> > > > > > > +	memcpy(formats_ptr(blob_data), formats, formats_size);
> > > > > > >
> > > > > > >  	mod = modifiers_ptr(blob_data);
> > > > > > > -	for (i = 0; i < plane->modifier_count; i++) {
> > > > > > > -		for (j = 0; j < plane->format_count; j++) {
> > > > > > > -			if (!plane->funcs->format_mod_supported ||
> > > > > > > +	for (i = 0; i < modifier_count; i++) {
> > > > > > > +		for (j = 0; j < format_count; j++) {
> > > > > > > +			if (is_async ||
> > > > > > > +			    !plane->funcs->format_mod_supported ||
> > > > > > >  			    plane->funcs-
> > >format_mod_supported(plane,
> > > > > > > -							       plane-
> > > > > > >format_types[j],
> > > > > > > -							       plane-
> > > > > > >modifiers[i])) {
> > > > > > > +							       formats[j],
> > > > > > > +
> > > modifiers[i])) {
> > > > > > >  				mod->formats |= 1ULL << j;
> > > > > > >  			}
> > > > > > >  		}
> > > > > > >
> > > > > > > -		mod->modifier = plane->modifiers[i];
> > > > > > > +		mod->modifier = modifiers[i];
> > > > > > >  		mod->offset = 0;
> > > > > > >  		mod->pad = 0;
> > > > > > >  		mod++;
> > > > > > >  	}
> > > > > > >
> > > > > > > -	drm_object_attach_property(&plane->base, config-
> > > > > > >modifiers_property,
> > > > > > > -				   blob->base.id);
> > > > > > > +	if (is_async)
> > > > > > > +		drm_object_attach_property(&plane->base,
> > > > > > > +					   config-
> > > >async_modifiers_property,
> > > > > > > +					   blob->base.id);
> > > > > > > +	else
> > > > > > > +		drm_object_attach_property(&plane->base,
> > > > > > > +					   config->modifiers_property,
> > > > > > > +					   blob->base.id);
> > > > > >
> > > > > > IMO the function should only create the blob. Leave it to the
> > > > > > caller to attach
> > > > > it.
> > > > > >
> > > > > Prior to this change for sync formats/modifiers the property
> > > > > attach was also done in the same function. So retained it as it.
> > > > >
> > > > > > The 'is_async' parameter could also be replaced with with a
> > > > > > function pointer to the appropriate format_mod_supported()
> > > > > > function. That makes the implementation entirely generic.
> > > > > >
> > > > > If the list of formats/modifiers for sync and async is passed to
> > > > > this function, then based on the list the corresponding function
> > > > > pointer can
> > > be called.
> > > > > This was done in the earlier patchset.
> > > > >
> > > > > > >
> > > > > > >  	return 0;
> > > > > > >  }
> > > > > > > +EXPORT_SYMBOL(drm_plane_create_format_blob);
> > > > > > >
> > > > > > >  /**
> > > > > > >   * DOC: hotspot properties
> > > > > > > @@ -476,7 +487,10 @@ static int
> > > > > > > __drm_universal_plane_init(struct
> > > > > > drm_device *dev,
> > > > > > >  	}
> > > > > > >
> > > > > > >  	if (format_modifier_count)
> > > > > > > -		create_in_format_blob(dev, plane);
> > > > > > > +		drm_plane_create_format_blob(dev, plane, plane-
> > > >modifiers,
> > > > > > > +					     format_modifier_count,
> > > > > > > +					     plane->format_types,
> > > > > > format_count,
> > > > > > > +					     false);
> > > > > > >
> > > > > > >  	return 0;
> > > > > > >  }
> > > > > > > diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> > > > > > > index
> > > > > > >
> > > > > >
> > > > >
> > >
> > e8749e6fc3bc0acfc73bbd8401f85c3126e86759..eb84830fbb723e39436bfbadf
> > > > > > 369
> > > > > > > 894a5657cd45 100644
> > > > > > > --- a/include/drm/drm_plane.h
> > > > > > > +++ b/include/drm/drm_plane.h
> > > > > > > @@ -1008,5 +1008,9 @@ int
> > > > > > > drm_plane_create_scaling_filter_property(struct drm_plane
> > > > > > > *plane, int
> > > > > > drm_plane_add_size_hints_property(struct drm_plane *plane,
> > > > > > >  				      const struct drm_plane_size_hint
> > *hints,
> > > > > > >  				      int num_hints);
> > > > > > > +int drm_plane_create_format_blob(struct drm_device *dev,
> > > > > > > +				 struct drm_plane *plane, u64
> > > *modifiers,
> > > > > > > +				 unsigned int modifier_count, u32
> > > *formats,
> > > > > > > +				 unsigned int format_count, bool
> > > is_async);
> > > > > >
> > > > > > I don't think this needs to be exposed to anyone.
> > > > > > __drm_universal_plane_init() should just populate both the
> > > > > > normal blob, and and the async blob (iff
> > > > > > .format_mod_supported_async() is provided).
> > > > > >
> > > > > Ok!
> > > > >
> > > > For __drm_universal_plane_init() to have both the sync/async
> > > format/modifiers list we will have to add new elements to struct
> > > drm_plane to hold the async formats/modifiers.
> > >
> > > No, you can just use the already existing format/modifier lists.
> > > .format_mod_supported_async() will filter out what's not wanted.
> > >
> > Agree, to populate the struct drm_format_modifier
> > .format_mod_supported_async along with the existing formats/modifier list
> > should be sufficient.
> > In case of async for the struct drm_format_modifier_blob the elements
> > format_offset includes the list of formats supported by async only. For this we
> > will need to have the static list. So can passing this list be done by adding new
> > elements in drm_plane specifically for async.
> 
> Just to add to Arun's point. We had this discussion on thread [1].
> 
> If we populate struct drm_format_modifier_blob for async using just the existing format/modifier lists in struct drm_plane,
> We will be mis-representing the following members of the structure to the user space
> 
> struct drm_format_modifier_blob {
>         /* Number of fourcc formats supported */
>         __u32 count_formats;
> 
>        /* Number of drm_format_modifiers */
>         __u32 count_modifiers;
> };

Nothing is misrepresentd. Those things just tell you what the bits in
the bimask mean.

> 
> However, as you correctly point out, it should still work because of the format-modifier bit mask.
> But it leaves the overall blob unnecessarily bloated (for example, with unnecessary entries in the format list).
> 
> We could however change the function in such a way that the loop
> 
> for (i = 0; i < modifier_count; i++) {
>                 for (j = 0; j < format_count; j++)
> 
> runs before filling up these members.
> 
> I am not sure how much juggling that would take but it could be a solution.
> 
> Anything you would suggest?

You're complicating things needlessly. The slightly bloated blob
should make no practical difference anywhere.

-- 
Ville Syrjälä
Intel