[PATCH] drm/atomic: Add connector atomic_check function.

Wed Apr 5 10:06:17 UTC 2017

On Wed, Apr 05, 2017 at 10:41:24AM +0200, Maarten Lankhorst wrote:
> The connector atomic check function may be called multiple times,
> or not at all. It's mostly useful for implementing properties but if you
> call check_modeset twice it can be used for other modeset related checks
> as well.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c      | 25 +++++++++++++++++----
>  include/drm/drm_modeset_helper_vtables.h | 37 ++++++++++++++++++++++++++++++++
>  2 files changed, 58 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index c3994b4d5f32..d550e79e8347 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -459,10 +459,20 @@ mode_fixup(struct drm_atomic_state *state)
>   *
>   * Check the state object to see if the requested state is physically possible.
>   * This does all the crtc and connector related computations for an atomic
> - * update and adds any additional connectors needed for full modesets and calls
> - * down into &drm_crtc_helper_funcs.mode_fixup and
> - * &drm_encoder_helper_funcs.mode_fixup or
> - * &drm_encoder_helper_funcs.atomic_check functions of the driver backend.
> + * update and adds any additional connectors needed for full modesets. It calls
> + * the various per-object callbacks in the follow order:
> + *
> + * 1. &drm_connector_helper_funcs.atomic_best_encoder for determining the new encoder.
> + * 2. &drm_connector_helper_funcs.atomic_check to validate the connector state.
> + * 3. If it's determined a modeset is needed then all connectors on the affected crtc
> + *    crtc are added.
> + * 4. &drm_bridge_funcs.mode_fixup is called on all encoder bridges.
> + * 5. &drm_encoder_helper_funcs.atomic_check is called to validate any encoder state.
> + *    This function is only called when the encoder will be part of a configured crtc,
> + *    it must not be used for implementing connector property validation.
> + *    If this function is NULL, &drm_atomic_encoder_helper_funcs.mode_fixup is called
> + *    instead.
> + * 6. &drm_crtc_helper_funcs.mode_fixup is called last, to fix up the mode with crtc constraints.

Line too I think. And maybe insert empty lines between each item, to make
them stand out more. Shouldn't affect rendering, but better to recheck.

>   *
>   * &drm_crtc_state.mode_changed is set when the input mode is changed.
>   * &drm_crtc_state.connectors_changed is set when a connector is added or
> @@ -522,6 +532,8 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
>  		return ret;
>  
>  	for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i) {
> +		const struct drm_connector_helper_funcs *funcs = connector->helper_private;
> +
>  		/*
>  		 * This only sets crtc->connectors_changed for routing changes,
>  		 * drivers must set crtc->connectors_changed themselves when
> @@ -539,6 +551,11 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
>  			    new_connector_state->link_status)
>  				new_crtc_state->connectors_changed = true;
>  		}
> +
> +		if (funcs->atomic_check)
> +			ret = funcs->atomic_check(connector, new_connector_state);
> +		if (ret)
> +			return ret;
>  	}
>  
>  	/*
> diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> index b304950b402d..7b5dd909f189 100644
> --- a/include/drm/drm_modeset_helper_vtables.h
> +++ b/include/drm/drm_modeset_helper_vtables.h
> @@ -860,6 +860,43 @@ struct drm_connector_helper_funcs {
>  	 */
>  	struct drm_encoder *(*atomic_best_encoder)(struct drm_connector *connector,
>  						   struct drm_connector_state *connector_state);
> +
> +	/**
> +	 * @atomic_check:
> +	 *
> +	 * Drivers should check connector properties in this
> +	 * hook. This function is called from &drm_atomic_helper_check_modeset.
> +	 *
> +	 * This function may not be called at all on a modeset or connector
> +	 * change, so it should only be used to validate properties.
> +	 * If it's required to validate all connectors from there, call
> +	 * &drm_atomic_helper_check_modeset twice. This will result in
> +	 * atomic_check possibly being called twice as well, which the callback
> +	 * should be made to handle correctly.
> +	 *
> +	 * This function is also allowed to inspect any other object's state and
> +	 * can add more state objects to the atomic commit if needed. Care must
> +	 * be taken though to ensure that state check and compute functions for
> +	 * these added states are all called, and derived state in other objects
> +	 * all updated. Again the recommendation is to just call check helpers
> +	 * until a maximal configuration is reached.

I think it'd be good to highlight setting connectors_changed from this
callback:

"If this callback determines that the property change requires a full
modeset, it can set &drm_crtc_state->connectors_changed to steer the
control flow in drm_atomic_helper_check_modeset()."

With those nits addressed, Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Would be good to get DK to r-b the patch too before merging, just for
practice and coordination.

Cheers, Daniel

> +	 *
> +	 * NOTE:
> +	 *
> +	 * This function is called in the check phase of an atomic update. The
> +	 * driver is not allowed to change anything outside of the free-standing
> +	 * state objects passed-in or assembled in the overall &drm_atomic_state
> +	 * update tracking structure.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * 0 on success, -EINVAL if the state or the transition can't be
> +	 * supported, -ENOMEM on memory allocation failure and -EDEADLK if an
> +	 * attempt to obtain another state object ran into a &drm_modeset_lock
> +	 * deadlock.
> +	 */
> +	int (*atomic_check)(struct drm_connector *connector,
> +			    struct drm_connector_state *state);
>  };
>  
>  /**
> -- 
> 2.7.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch