linux-kernel - Re: [PATCH 23/29] drm/bridge: Provide a helper to retrieve current bridge state

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Message-ID: <20250116-steady-masterful-basilisk-6defca@houat>
Date: Thu, 16 Jan 2025 09:30:58 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Douglas Anderson <dianders@...omium.org>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 23/29] drm/bridge: Provide a helper to retrieve current
 bridge state

Hi,

On Thu, Jan 16, 2025 at 02:43:37AM +0200, Dmitry Baryshkov wrote:
> On Wed, Jan 15, 2025 at 10:05:30PM +0100, Maxime Ripard wrote:
> > The current bridge state is accessible from the drm_bridge structure,
> > but since it's fairly indirect it's not easy to figure out.
> > 
> > Provide a helper to retrieve it.
> > 
> > Signed-off-by: Maxime Ripard <mripard@...nel.org>
> > ---
> >  include/drm/drm_bridge.h | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> > index 8e18130be8bb85fc2463917dde9bf1d281934184..95c5037a6335e4c1be511e6c31308202015c7754 100644
> > --- a/include/drm/drm_bridge.h
> > +++ b/include/drm/drm_bridge.h
> > @@ -955,10 +955,27 @@ static inline struct drm_bridge *of_drm_find_bridge(struct device_node *np)
> >  {
> >  	return NULL;
> >  }
> >  #endif
> >  
> > +/**
> > + * @drm_bridge_get_current_state() - Get the current bridge state
> > + * @bridge: bridge object
> > + *
> > + * RETURNS:
> > + *
> > + * The current bridge state, or NULL if there is none.
> 
> Are there any kind of limitations on when and how this function can be
> used? I don't think we can be accessing the state randomly, as the
> framework can change it at some points. E.g. what if the driver uses
> this state from audio or cec callbacks, while the DRM framework performs
> atomic commit and changes / frees the state right concurrently?

The semantics are equivalent to drm_connector->state, drm_crtc->state,
etc, but I'm not sure we ever defined it clearly.

Also, it looks like I can never remember what the locking rules are :)
It looks like a good occasion to ask Sima and write some more
documentation.

Thanks!
Maxime

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