Re: [RFC PATCH v3 2/3] drm: add support modifiers for drivers whose planes only support linear layout

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hello Esaki-san,

Thank you for the patch.

On Fri, Jan 14, 2022 at 07:17:52PM +0900, Tomohito Esaki wrote:
> The LINEAR modifier is advertised as default if a driver doesn't specify
> modifiers.
> 
> Signed-off-by: Tomohito Esaki <etom@igel.co.jp>
> ---
>  drivers/gpu/drm/drm_plane.c | 15 ++++++++++++---
>  include/drm/drm_plane.h     |  3 +++
>  2 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> index deeec60a3315..5aa7e241971e 100644
> --- a/drivers/gpu/drm/drm_plane.c
> +++ b/drivers/gpu/drm/drm_plane.c
> @@ -237,6 +237,10 @@ 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[] = {

This can be static.

> +		DRM_FORMAT_MOD_LINEAR,
> +		DRM_FORMAT_MOD_INVALID

No need for a terminator here. The terminator is needed in the
format_modifiers array passed to this function, to count the number of
elements, but the default_modifiers is used with a hard-coded count.

> +	};
>  	unsigned int format_modifier_count = 0;
>  	int ret;
>  
> @@ -277,6 +281,11 @@ 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;

You can use

			format_modifier_count = ARRAY_SIZE(default_modifiers);

> +		}
>  	}
>  
>  	/* autoset the cap and check for consistency across all planes */
> @@ -341,7 +350,7 @@ 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;
> @@ -368,8 +377,8 @@ 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.

I'd write this a bit differently:

 * Drivers that only support the DRM_FORMAT_MOD_LINEAR modifier support may set
 * @format_modifiers to NULL. The plane will advertise the linear modifier.

As fb_modifiers_not_supported is only for a few legacy drivers, I
wouldn't even mention it here, it would only obfuscate things.

>   *
>   * Returns:
>   * Zero on success, error code on failure.
> 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.

Same here.

With these small issues addressed,

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> + *
>   * Returns:
>   * Pointer to new plane, or ERR_PTR on failure.
>   */

-- 
Regards,

Laurent Pinchart