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

[Daniel Vetter]

On Fri, May 12, 2017 at 12:53:56PM +0300, Laurent Pinchart wrote:
> Hi Daniel,
> 
> On Wednesday 10 May 2017 19:55:56 Daniel Vetter wrote:
> > 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 :(
> 
> How about documenting the expected driver behaviour in details ? I won't 
> volunteer as I have to confess it's not clear to me what we expect from 
> drivers.

It already is? Or where exactly is it lacking in the docs?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch