Re: [RFC PATH 1/3] drm: add support modifiers for drivers whose planes only support linear layout

[Esaki Tomohito <etom@xxxxxxxxxx>]

Thank you for your reviews.

On 2022/01/15 1:50, Daniel Vetter wrote:
> On Wed, Dec 22, 2021 at 02:27:25PM +0900, Tomohito Esaki wrote:
> > The LINEAR modifier is advertised as default if a driver doesn't specify
> > modifiers. However, there are legacy drivers such as radeon that do not
> > support modifiers but infer the actual layout of the underlying buffer.
> > Therefore, a new flag not_support_fb_modifires is introduced for these
> > legacy drivers. Allow_fb_modifiers will be replaced with this new flag.
> >
> > Signed-off-by: Tomohito Esaki <etom@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/drm_plane.c   | 34 ++++++++++++++++++++++++++--------
> >   include/drm/drm_mode_config.h | 10 ++++++++++
> >   include/drm/drm_plane.h       |  3 +++
> >   3 files changed, 39 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> > index 82afb854141b..75308ee240c0 100644
> > --- a/drivers/gpu/drm/drm_plane.c
> > +++ b/drivers/gpu/drm/drm_plane.c
> > @@ -161,6 +161,16 @@ modifiers_ptr(struct drm_format_modifier_blob *blob)
> >   	return (struct drm_format_modifier *)(((char *)blob) + blob->modifiers_offset);
> >   }
> >   
> > +static bool check_format_modifier(struct drm_plane *plane, uint32_t format,
> > +				  uint64_t modifier)
> > +{
> > +	if (plane->funcs->format_mod_supported)
> > +		return plane->funcs->format_mod_supported(plane, format,
> > +							  modifier);
> > +
> > +	return modifier == DRM_FORMAT_MOD_LINEAR;
> > +}
> > +
> >   static int create_in_format_blob(struct drm_device *dev, struct drm_plane *plane)
> >   {
> >   	const struct drm_mode_config *config = &dev->mode_config;
> > @@ -203,16 +213,15 @@ static int create_in_format_blob(struct drm_device *dev, struct drm_plane *plane
> >   	memcpy(formats_ptr(blob_data), plane->format_types, formats_size);
> >   
> >   	/* If we can't determine support, just bail */
> > -	if (!plane->funcs->format_mod_supported)
> > +	if (config->fb_modifiers_not_supported)
> >   		goto done;
> >   
> >   	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(plane,
> > -							       plane->format_types[j],
> > -							       plane->modifiers[i])) {
> > -
> > +			if (check_format_modifier(plane,
> > +						  plane->format_types[j],
> > +						  plane->modifiers[i])) {
> >   				mod->formats |= 1ULL << j;
> >   			}
> >   		}
> > @@ -242,6 +251,10 @@ static int __drm_universal_plane_init(struct drm_device *dev,
> >   				      const char *name, va_list ap)
> >   {
> >   	struct drm_mode_config *config = &dev->mode_config;
> > +	const uint64_t default_modifiers[] = {
> > +		DRM_FORMAT_MOD_LINEAR,
> > +		DRM_FORMAT_MOD_INVALID
> > +	};
> >   	unsigned int format_modifier_count = 0;
> >   	int ret;
> >   
> > @@ -282,6 +295,11 @@ static int __drm_universal_plane_init(struct drm_device *dev,
> >   
> >   		while (*temp_modifiers++ != DRM_FORMAT_MOD_INVALID)
> >   			format_modifier_count++;
> > +	} else {
> > +		if (!dev->mode_config.fb_modifiers_not_supported) {
> > +			format_modifiers = default_modifiers;
> > +			format_modifier_count = 1;
> > +		}
> >   	}
> >   
> >   	/* autoset the cap and check for consistency across all planes */
> > @@ -346,7 +364,7 @@ static int __drm_universal_plane_init(struct drm_device *dev,
> >   		drm_object_attach_property(&plane->base, config->prop_src_h, 0);
> >   	}
> >   
> > -	if (config->allow_fb_modifiers)
> > +	if (format_modifier_count)
> >   		create_in_format_blob(dev, plane);
> >   
> >   	return 0;
> > @@ -373,8 +391,8 @@ static int __drm_universal_plane_init(struct drm_device *dev,
> >    * drm_universal_plane_init() to let the DRM managed resource infrastructure
> >    * take care of cleanup and deallocation.
> >    *
> > - * Drivers supporting modifiers must set @format_modifiers on all their planes,
> > - * even those that only support DRM_FORMAT_MOD_LINEAR.
> > + * For drivers supporting modifiers, all planes will advertise
> > + * DRM_FORMAT_MOD_LINEAR support, if @format_modifiers is not set.
> >    *
> >    * Returns:
> >    * Zero on success, error code on failure.
> > diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> > index 48b7de80daf5..c56f298c55bd 100644
> > --- a/include/drm/drm_mode_config.h
> > +++ b/include/drm/drm_mode_config.h
> > @@ -920,6 +920,16 @@ struct drm_mode_config {
> >   	 */
> >   	bool allow_fb_modifiers;
> >   
> > +	/**
> > +	 * @fb_modifiers_not_supported:
> > +	 *
> > +	 * This flag is for legacy drivers such as radeon that do not support
>
> Maybe don't put specific driver names into kerneldoc (in commit message to
> motivate your changes it's fine). It's unlikely radeon ever changes on
> this, but also no one will update this in the docs if we ever do that.
>
> Perhaps also add that new driver should never set this, just to hammer it
> home that modifiers really should work everywhere.

I agree with you.
I'll modify this docs.

Thanks,
Tomohito Esaki

> Otherwise I think this series is the right thing to do.
> -Daniel
>
> > +	 * modifiers but infer the actual layout of the underlying buffer.
> > +	 * Generally, each drivers must support modifiers, this flag should not
> > +	 * be set.
> > +	 */
> > +	bool fb_modifiers_not_supported;
> > +
> >   	/**
> >   	 * @normalize_zpos:
> >   	 *
> > diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> > index 0c1102dc4d88..cad641b1f797 100644
> > --- a/include/drm/drm_plane.h
> > +++ b/include/drm/drm_plane.h
> > @@ -803,6 +803,9 @@ void *__drmm_universal_plane_alloc(struct drm_device *dev,
> >    *
> >    * The @drm_plane_funcs.destroy hook must be NULL.
> >    *
> > + * For drivers supporting modifiers, all planes will advertise
> > + * DRM_FORMAT_MOD_LINEAR support, if @format_modifiers is not set.
> > + *
> >    * Returns:
> >    * Pointer to new plane, or ERR_PTR on failure.
> >    */
> > --
> > 2.17.1