Re: [PATCH 25/29] drm/bridge: Provide pointers to the connector and crtc in bridge state

[Maxime Ripard <mripard@kernel.org>]

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Hi,

On Thu, Jan 16, 2025 at 03:04:19AM +0200, Dmitry Baryshkov wrote:
> On Wed, Jan 15, 2025 at 10:05:32PM +0100, Maxime Ripard wrote:
> > Now that connectors are no longer necessarily created by the bridges
> > drivers themselves but might be created by drm_bridge_connector, it's
> > pretty hard for bridge drivers to retrieve pointers to the connector and
> > CRTC they are attached to.
> > 
> > Indeed, the only way to retrieve the CRTC is to follow the drm_bridge
> > encoder field, and then the drm_encoder crtc field, both of them being
> > deprecated.
> > 
> > And for the connector, since we can have multiple connectors attached to
> > a CRTC, we don't really have a reliable way to get it.
> > 
> > Let's provide both pointers in the drm_bridge_state structure so we
> > don't have to follow deprecated, non-atomic, pointers, and be more
> > consistent with the other KMS entities.
> > 
> > Signed-off-by: Maxime Ripard <mripard@kernel.org>
> > ---
> >  drivers/gpu/drm/drm_atomic_state_helper.c |  5 +++++
> >  drivers/gpu/drm/drm_bridge.c              | 21 +++++++++++++--------
> >  include/drm/drm_atomic.h                  | 14 ++++++++++++++
> >  3 files changed, 32 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> > index 519228eb109533d2596e899a57b571fa0995824f..66661dca077215b78dffca7bc1712f56d35e3918 100644
> > --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> > @@ -777,10 +777,15 @@ EXPORT_SYMBOL(drm_atomic_helper_bridge_duplicate_state);
> >   * that don't subclass the bridge state.
> >   */
> >  void drm_atomic_helper_bridge_destroy_state(struct drm_bridge *bridge,
> >  					    struct drm_bridge_state *state)
> >  {
> > +	if (state->connector) {
> > +		drm_connector_put(state->connector);
> > +		state->connector = NULL;
> > +	}
> > +
> >  	kfree(state);
> >  }
> >  EXPORT_SYMBOL(drm_atomic_helper_bridge_destroy_state);
> >  
> >  /**
> > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > index c937980d6591fd98e33e37d799ebf84e7e6c5529..069c105aa59636c64caffbefcf482133b0db97d9 100644
> > --- a/drivers/gpu/drm/drm_bridge.c
> > +++ b/drivers/gpu/drm/drm_bridge.c
> > @@ -829,19 +829,24 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_enable);
> >  
> >  static int drm_atomic_bridge_check(struct drm_bridge *bridge,
> >  				   struct drm_crtc_state *crtc_state,
> >  				   struct drm_connector_state *conn_state)
> >  {
> > +	struct drm_bridge_state *bridge_state;
> > +	int ret;
> > +
> > +	bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state,
> > +						       bridge);
> 
> It felt like an error to me to call this function for a non-atomic
> bridges, until I fully followed the code path to find that it will
> return NULL if the bridge isn't registered as a private object.

Yeah.. I wasn't too sure what to do about this one either. I think it
would be more consistent to always have a state properly filled, even if
we have !atomic drivers. It's what happens with the rest of the
framework.

But also, I have no idea what the side-effects might be.

One thing though: a driver having an atomic_check callback is not an
indication of whether it supports atomic mode-setting or not.
atomic_check is optional, so we can have atomic drivers without
atomic_check.

> BTW: if my grep-foo isn't deceiving me, we currently have 34 non-atomic
> bridges out of 90. Should we start forcebly updating them to use atomic
> interface in attempt to drop the mode_fixup() and other non-atomic
> callbacks?

Maybe? I'm not sure forcing anyone to anything really helps. sii8620 for
example is going to be a fun one, and I'd rather stay away from it :)

Maxime

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