Re: [PATCH v2 7/8] drm: Use mode_valid() in atomic modeset

[Daniel Vetter]

On Wed, May 10, 2017 at 09:38:00PM +0530, Archit Taneja wrote:
> 
> 
> On 5/9/2017 10:30 PM, Jose Abreu wrote:
> > This patches makes use of the new mode_valid() callbacks introduced
> > previously to validate the full video pipeline when modesetting.
> > 
> > This calls the connector->mode_valid(), encoder->mode_valid(),
> > bridge->mode_valid() and crtc->mode_valid() so that we can
> > make sure that the mode will be accepted in every components.
> > 
> > Signed-off-by: Jose Abreu <joabreu@xxxxxxxxxxxx>
> > Cc: Carlos Palminha <palminha@xxxxxxxxxxxx>
> > Cc: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
> > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > Cc: Dave Airlie <airlied@xxxxxxxx>
> > Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> > Cc: Archit Taneja <architt@xxxxxxxxxxxxxx>
> > ---
> > 
> > Changes v1->v2:
> > 	- Removed call to connector->mode_valid (Ville, Daniel)
> > 	- Change function name (Ville)
> > 	- Use for_each_new_connector_in_state (Ville)
> > 	- Do not validate if connector and mode didn't change (Ville)
> > 	- Use new helpers to call mode_valid
> > 
> >   drivers/gpu/drm/drm_atomic_helper.c | 75 +++++++++++++++++++++++++++++++++++--
> >   1 file changed, 72 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 8be9719..19d0ea1 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -452,6 +452,69 @@ static int handle_conflicting_encoders(struct drm_atomic_state *state,
> >   	return 0;
> >   }
> > +static enum drm_mode_status mode_valid_path(struct drm_connector *connector,
> > +					    struct drm_encoder *encoder,
> > +					    struct drm_crtc *crtc,
> > +					    struct drm_display_mode *mode)
> > +{
> > +	enum drm_mode_status ret;
> > +
> > +	ret = drm_encoder_mode_valid(encoder, mode);
> > +	if (ret != MODE_OK) {
> > +		DRM_DEBUG_ATOMIC("[ENCODER:%d:%s] mode_valid() failed\n",
> > +				encoder->base.id, encoder->name);
> > +		return ret;
> > +	}
> > +
> > +	ret = drm_bridge_mode_valid(encoder->bridge, mode);
> > +	if (ret != MODE_OK) {
> > +		DRM_DEBUG_ATOMIC("[BRIDGE] mode_valid() failed\n");
> > +		return ret;
> > +	}
> > +
> > +	ret = drm_crtc_mode_valid(crtc, mode);
> > +	if (ret != MODE_OK) {
> > +		DRM_DEBUG_ATOMIC("[CRTC:%d:%s] mode_valid() failed\n",
> > +				crtc->base.id, crtc->name);
> > +		return ret;
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> > +static int
> > +mode_valid(struct drm_atomic_state *state)
> > +{
> > +	struct drm_connector_state *conn_state;
> > +	struct drm_connector *connector;
> > +	int i;
> > +
> > +	for_each_new_connector_in_state(state, connector, conn_state, i) {
> > +		struct drm_encoder *encoder = conn_state->best_encoder;
> > +		struct drm_crtc *crtc = conn_state->crtc;
> > +		struct drm_crtc_state *crtc_state;
> > +		enum drm_mode_status mode_status;
> > +		struct drm_display_mode *mode;
> > +
> > +		if (!crtc || !encoder)
> > +			continue;
> > +
> > +		crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
> > +		if (!crtc_state)
> > +			continue;
> > +		if (!crtc_state->mode_changed && !crtc_state->connectors_changed)
> > +			continue;
> > +
> > +		mode = &crtc_state->mode;
> > +
> > +		mode_status = mode_valid_path(connector, encoder, crtc, mode);
> > +		if (mode_status != MODE_OK)
> > +			return -EINVAL;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >   /**
> >    * drm_atomic_helper_check_modeset - validate state object for modeset changes
> >    * @dev: DRM device
> > @@ -466,13 +529,15 @@ static int handle_conflicting_encoders(struct drm_atomic_state *state,
> >    * 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 and &drm_connector_helper_funcs.atomic_check is run on them.
> > - * 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.
> > + * 4. &drm_encoder_helper_funcs.mode_valid, &drm_bridge_funcs.mode_valid and
> > + *    &drm_crtc_helper_funcs.mode_valid are called on the affected components.
> > + * 5. &drm_bridge_funcs.mode_fixup is called on all encoder bridges.
> > + * 6. &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.
> > + * 7. &drm_crtc_helper_funcs.mode_fixup is called last, to fix up the mode with crtc constraints.
> >    *
> >    * &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
> > @@ -617,6 +682,10 @@ static int handle_conflicting_encoders(struct drm_atomic_state *state,
> >   			return ret;
> >   	}
> > +	ret = mode_valid(state);
> > +	if (ret)
> > +		return ret;
> > +
> 
> Since we've ensured that the modes won't fail, can mode_fixup() and
> the mode_fixup() ops for crtc/bridge/encoders be assured to not fail
> too? This is assuming that all drivers have moved to using the new
> mode_valid() ops correctly.

The entire point of re-checking is that userspace can create its own modes
and submit them to the kernel, bypassing the current
connector->mode_valid() check. I think almost all drivers get this wrong
unfortunately :(
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch