linux-kernel - Re: [PATCH v3 08/10] drm/display: bridge-connector: handle CEC adapters

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Message-ID: <abbyf3h4weoshu63mrdwy4vmm3z4t3vb74ikvcnk3lhptlxhm7@bdcj4a3cxpzu>
Date: Wed, 29 Jan 2025 20:32:46 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Neil Armstrong <neil.armstrong@...aro.org>
Cc: Maxime Ripard <mripard@...nel.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Dave Stevenson <dave.stevenson@...pberrypi.com>, Maíra Canal <mcanal@...lia.com>, 
	Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Robert Foss <rfoss@...nel.org>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
	Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 08/10] drm/display: bridge-connector: handle CEC
 adapters

On Wed, Jan 29, 2025 at 05:44:31PM +0100, Neil Armstrong wrote:
> On 29/01/2025 00:44, Dmitry Baryshkov wrote:
> > On Tue, Jan 28, 2025 at 05:14:06PM +0100, Maxime Ripard wrote:
> > > On Sun, Jan 26, 2025 at 03:29:13PM +0200, Dmitry Baryshkov wrote:
> > > >   /* -----------------------------------------------------------------------------
> > > >    * Bridge Connector Initialisation
> > > >    */
> > > > @@ -633,6 +711,21 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
> > > >   			if (ret)
> > > >   				return ERR_PTR(ret);
> > > >   		}
> > > > +
> > > > +		if (bridge->hdmi_cec_adapter_name) {
> > > > +			if (!bridge->funcs->hdmi_cec_enable ||
> > > > +			    !bridge->funcs->hdmi_cec_log_addr ||
> > > > +			    !bridge->funcs->hdmi_cec_transmit)
> > > > +				return ERR_PTR(-EINVAL);
> > > > +
> > > > +			ret = drm_connector_hdmi_cec_register(connector,
> > > > +							      &drm_bridge_connector_hdmi_cec_ops,
> > > > +							      bridge->hdmi_cec_adapter_name,
> > > > +							      bridge->hdmi_cec_available_las,
> > > > +							      bridge->hdmi_dev);
> > > > +			if (ret)
> > > > +				return ERR_PTR(ret);
> > > > +		}
> > > 
> > > Maybe we can use a different bridge feature flag to trigger the CEC code
> > > support instead?
> > 
> > it is possible, but what is the possible usecase? DP drivers should be
> > using DP_AUX CEC instead. And I think there are no other kinds of
> > bridges which implement CEC support. Meson driver does something strange
> > by registering CEC notifier from meson_encoder_hdmi. I think instead
> > this should be moved to the DW HDMI bridge itself
> 
> It was done before bridge_connector has any support for CEC to keep the
> functionnality, I'll be happy to switch to this.

Well... Converting dw-hdmi to use all HDMI API is going to be
interesting anyway:

- iMX8, iMX6 attach with flags=0, so dw-hdmi creates connector (with all
  its fanciness).
- Ingenic and RCAR-DU use simple drm_bridge_connector, so they will just
  get all new features.
- Meson uses drm_bridge_connector + additional bits on top of it (like
  CEC, max_bpc, HDR).

Either we end up with a monstruous commit that reworks dw-hdmi _and_
drop extra bits from meson driver at the same time or we need some
well-thought plan. For example, first make some of the features of Meson
optional and dependent on their generic counterparts being registered by
drm_bridge_connector, then convert dw-hdmi _and_ use
drm_bridge_connector internally, finally drop extra meson features now
consumed by the core.


-- 
With best wishes
Dmitry