Re: [PATCH v3 02/10] drm: Add drm_atomic_crtc_state_for_encoder helper

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, May 03, 2019 at 04:06:28PM +0200, Daniel Vetter wrote:
> On Fri, May 3, 2019 at 2:47 PM Sean Paul <sean@poorly.run> wrote:
> > On Fri, May 03, 2019 at 10:18:51AM +0200, Daniel Vetter wrote:
> > > On Thu, May 02, 2019 at 03:49:44PM -0400, Sean Paul wrote:
> > > > From: Sean Paul <seanpaul@chromium.org>
> > > >
> > > > This patch adds a helper to tease out the currently connected crtc for
> > > > an encoder, along with its state. This follows the same pattern as the
> > > > drm_atomic_crtc_*_for_* macros in the atomic helpers. Since the
> > > > relationship of crtc:encoder is 1:n, we don't need a loop since there is
> > > > only one crtc per encoder.
> > >
> > > No idea which macros you mean, couldn't find them.
> >
> > No longer relevant with the changes below, but for completeness, I was trying to
> > refer to drm_atomic_crtc_state_for_each_plane and friends. I see now that I
> > wasn't terribly clear :)
> >
> >
> > > >
> > > > Instead of splitting this into 3 functions which all do the same thing,
> > > > this is presented as one function. Perhaps that's too ugly and it should
> > > > be split to:
> > > > struct drm_crtc *drm_atomic_crtc_for_encoder(state, encoder);
> > > > struct drm_crtc_state *drm_atomic_new_crtc_state_for_encoder(state, encoder);
> > > > struct drm_crtc_state *drm_atomic_old_crtc_state_for_encoder(state, encoder);
> > > >
> > > > Suggestions welcome.
> > > >
> > > > Changes in v3:
> > > > - Added to the set
> > > >
> > > > Cc: Daniel Vetter <daniel@ffwll.ch>
> > > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > Signed-off-by: Sean Paul <seanpaul@chromium.org>
> > > > ---
> > > >  drivers/gpu/drm/drm_atomic_helper.c | 48 +++++++++++++++++++++++++++++
> > > >  include/drm/drm_atomic_helper.h     |  6 ++++
> > > >  2 files changed, 54 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > > > index 71cc7d6b0644..1f81ca8daad7 100644
> > > > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > > > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > > > @@ -3591,3 +3591,51 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
> > > >     return ret;
> > > >  }
> > > >  EXPORT_SYMBOL(drm_atomic_helper_legacy_gamma_set);
> > > > +
> > > > +/**
> > > > + * drm_atomic_crtc_state_for_encoder - Get crtc and new/old state for an encoder
> > > > + * @state: Atomic state
> > > > + * @encoder: The encoder to fetch the crtc information for
> > > > + * @crtc: If not NULL, receives the currently connected crtc
> > > > + * @old_crtc_state: If not NULL, receives the crtc's old state
> > > > + * @new_crtc_state: If not NULL, receives the crtc's new state
> > > > + *
> > > > + * This function finds the crtc which is currently connected to @encoder and
> > > > + * returns it as well as its old and new state. If there is no crtc currently
> > > > + * connected, the function will clear @crtc, @old_crtc_state, @new_crtc_state.
> > > > + *
> > > > + * All of @crtc, @old_crtc_state, and @new_crtc_state are optional.
> > > > + */
> > > > +void drm_atomic_crtc_state_for_encoder(struct drm_atomic_state *state,
> > > > +                                  struct drm_encoder *encoder,
> > > > +                                  struct drm_crtc **crtc,
> > > > +                                  struct drm_crtc_state **old_crtc_state,
> > > > +                                  struct drm_crtc_state **new_crtc_state)
> > > > +{
> > > > +   struct drm_crtc *tmp_crtc;
> > > > +   struct drm_crtc_state *tmp_new_crtc_state, *tmp_old_crtc_state;
> > > > +   u32 enc_mask = drm_encoder_mask(encoder);
> > > > +   int i;
> > > > +
> > > > +   for_each_oldnew_crtc_in_state(state, tmp_crtc, tmp_old_crtc_state,
> > > > +                                 tmp_new_crtc_state, i) {
> > >
> > > So there's two ways to do this:
> > >
> > > - Using encoder_mask, which is a helper thing. In that case I'd rename
> > >   this to drm_atomic_helper_crtc_for_encoder.
> > >
> > > - By looping over the connectors, and looking at ->best_encoder and
> > >   ->crtc, see drm_encoder_get_crtc in drm_encoder.c. That's the core way
> > >   of doing things. In that case call it drm_atomic_crtc_for_encoder, and
> > >   put it into drm_atomic.c.
> > >
> > > There's two ways of doing the 2nd one: looping over connectors in a
> > > drm_atomic_state, or the connector list overall. First requires that the
> > > encoder is already in drm_atomic_state (which I think makes sense).
> >
> > Yeah, I wasn't particularly interested in encoders not in state. I had
> > considered going the connector route, but since you can have multiple connectors
> > per encoder, going through crtc seemed a bit more direct.
> 
> You can have multiple possible connectors for a given encoder, and
> multiple possible encoders for a given connector. In both cases the
> driver picks for you. But for active encoders and connectors the
> relationship is 1:1. That's what the helpers exploit by looping over
> connectors to get at encoders.
> 
> > > Even more complications on old/new_crtc_state: Is that the old state for
> > > the old crtc, or the old state for the new crtc (that can switch too).
> > > Same for the new crtc state ...
> > >
> > > tldr; I'd create 2 functions:
> > >
> > > drm_crtc *drm_atomic_encoder_get_new_crtc(drm_atomic_state *state, encoder)
> > > drm_crtc *drm_atomic_encoder_get_old_crtc(drm_atomic_state *state, encoder)
> > >
> > > With the requirement that they'll return NULL if the encder isn't in in
> > > @state, and implemented using looping over connectors in @state.
> >
> > It seems like we could just tweak this function a bit to get the new or old crtc
> > for an encoder. Any particular reason for going through connector instead? Is it
> > to avoid the encoder_mask which is a helper thing? In that case, perhaps this
> > should use connector links and live in drm_atomic.c?
> 
> Well as explained, there's 3 ways you can achieve the same really. I
> do think the "loop over connectors in drm_atomic_state, WARN() if we
> haven't found the encoder you want the crtc for" is probably the most
> solid aproach since it picks up a core atomic concept. But the others
> (looping the connector list, or looping encoder_mask) all work too.
> 
> Aside: plane/encoder_mask was added to go from crtc to
> planes/encoders, not really to go the other way round.
> 
> Another solution would be to pass the connector_state to all atomic
> encoder hooks, then you could just look at connector_state->crtc. Plus
> you can get at all the other interesting bits and pieces of
> information. In a way this is fallout from us keeping encoders as a
> meaningful concept for easier transition of legacy drivers, while
> still keeping them entirely irrelevant for the actual userspace api
> semantics.
> 
> So maybe we want drm_atomic_encoder_get_old/new_connector here. Or
> maybe we even want the full set of functions, i.e.
> drm_atomic_encoder_get_old/new_connector/crtc.

Laurent just asked me on irc how to get from a bridge to connector
information. Bridge knows its encoder (it's static), so a encode2connector
function would already have a 2nd user with this.

I.e. I'd say +1 on that approach, and then you can get at the connector
state and whatever else you feel like from there?

Adding Laurent.
-Daniel

> 
> In all cases I think only returning the object, not it's state is
> simplest, since then you avoid the confusion of old/new state for
> old/new obj.
> -Daniel
> 
> 
> > Thanks for the review!
> >
> > Sean
> >
> > >
> > > tldr; this is a lot more tricky than it looks like ...
> > > -Daniel
> > >
> > >
> > > > +           if (!(tmp_new_crtc_state->encoder_mask & enc_mask))
> > > > +                   continue;
> > > > +
> > > > +           if (new_crtc_state)
> > > > +                   *new_crtc_state = tmp_new_crtc_state;
> > > > +           if (old_crtc_state)
> > > > +                   *old_crtc_state = tmp_old_crtc_state;
> > > > +           if (crtc)
> > > > +                   *crtc = tmp_crtc;
> > > > +           return;
> > > > +   }
> > > > +
> > > > +   if (new_crtc_state)
> > > > +           *new_crtc_state = NULL;
> > > > +   if (old_crtc_state)
> > > > +           *old_crtc_state = NULL;
> > > > +   if (crtc)
> > > > +           *crtc = NULL;
> > > > +}
> > > > +EXPORT_SYMBOL(drm_atomic_crtc_state_for_encoder);
> > > > diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
> > > > index 58214be3bf3d..2383550a0cc8 100644
> > > > --- a/include/drm/drm_atomic_helper.h
> > > > +++ b/include/drm/drm_atomic_helper.h
> > > > @@ -153,6 +153,12 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
> > > >                                    uint32_t size,
> > > >                                    struct drm_modeset_acquire_ctx *ctx);
> > > >
> > > > +void drm_atomic_crtc_state_for_encoder(struct drm_atomic_state *state,
> > > > +                                  struct drm_encoder *encoder,
> > > > +                                  struct drm_crtc **crtc,
> > > > +                                  struct drm_crtc_state **old_crtc_state,
> > > > +                                  struct drm_crtc_state **new_crtc_state);
> > > > +
> > > >  /**
> > > >   * drm_atomic_crtc_for_each_plane - iterate over planes currently attached to CRTC
> > > >   * @plane: the loop cursor
> > > > --
> > > > Sean Paul, Software Engineer, Google / Chromium OS
> > > >
> > >
> > > --
> > > Daniel Vetter
> > > Software Engineer, Intel Corporation
> > > http://blog.ffwll.ch
> >
> > --
> > Sean Paul, Software Engineer, Google / Chromium OS
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch