linux-kernel - Re: [PATCH v1 23/35] drm/vc4: vec: Convert to the new TV mode property

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Date:   Mon, 29 Aug 2022 14:13:53 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Noralf Trønnes <noralf@...nnes.org>
Cc:     Jernej Skrabec <jernej.skrabec@...il.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jerome Brunet <jbrunet@...libre.com>,
        Samuel Holland <samuel@...lland.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel@...ll.ch>, Emma Anholt <emma@...olt.net>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Phil Elwell <phil@...pberrypi.com>,
        Mateusz Kwiatkowski <kfyatek+publicgit@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-amlogic@...ts.infradead.org, dri-devel@...ts.freedesktop.org,
        Dom Cobley <dom@...pberrypi.com>
Subject: Re: [PATCH v1 23/35] drm/vc4: vec: Convert to the new TV mode
 property

Hi Noralf,

On Thu, Aug 25, 2022 at 03:14:01PM +0200, Noralf Trønnes wrote:
> Den 24.08.2022 17.26, skrev Maxime Ripard:
> > On Sat, Aug 20, 2022 at 07:22:48PM +0200, Noralf Trønnes wrote:
> >> Den 29.07.2022 18.35, skrev Maxime Ripard:
> >>> Now that the core can deal fine with analog TV modes, let's convert the vc4
> >>> VEC driver to leverage those new features.
> >>>
> >>> We've added some backward compatibility to support the old TV mode property
> >>> and translate it into the new TV norm property.
> >>>
> >>> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> >>>
> >>> diff --git a/drivers/gpu/drm/vc4/vc4_vec.c b/drivers/gpu/drm/vc4/vc4_vec.c
> >>
> >>>  static int vc4_vec_connector_get_modes(struct drm_connector *connector)
> >>>  {
> >>> -	struct drm_connector_state *state = connector->state;
> >>>  	struct drm_display_mode *mode;
> >>>  
> >>> -	mode = drm_mode_duplicate(connector->dev,
> >>> -				  vc4_vec_tv_modes[state->tv.mode].mode);
> >>> +	mode = drm_mode_duplicate(connector->dev, &drm_mode_480i);
> >>> +	if (!mode) {
> >>> +		DRM_ERROR("Failed to create a new display mode\n");
> >>> +		return -ENOMEM;
> >>> +	}
> >>> +
> >>> +	drm_mode_probed_add(connector, mode);
> >>> +
> >>> +	mode = drm_mode_duplicate(connector->dev, &drm_mode_576i);
> >>
> >> Maybe the mode that matches tv.norm should be marked as preferred so
> >> userspace knows which one to pick?
> > 
> > I'm not sure how realistic that would be. Doing this based on the driver
> > / cmdline preference is going to be fairly easy, but then it's a
> > property, it's going to be updated, and we probably don't want to mess
> > around the mode flags based on new property values?
> > 
> 
> Strictly speaking we need to fire an event to userspace if the mode
> changes, and this is probably not straightforward to do underneath
> modeset locks, would probably need a worker.

I'm not sure this would work in all cases. Kodi for example doesn't
handle hotplug events at all, so we might end up in situations where the
state is not consistent anymore.

Even if we were to only expose one mode to the userspace, depending on
the current TV mode, userspace could still end up trying to push a mode
into KMS that isn't the one we expose anymore, so I'm not sure we can
solve this entirely.

> Clever userspace like GNOME will try to use the active mode, so it will
> handle this that way. If someone has set up the pipeline first that is.
> drm_client/fbdev and plymouth can do that because they honour userdef modes.
> 
> Other userspace that don't know the userdef flag will fallback to the
> first mode which is NTSC which is also the default tvmode, so maybe this
> is good enough. PAL users will have to specify the mode, or teach their
> program about the userdef flag.
> 
> But ofc relying on the userdef flag depends on the fact that there's a
> mode on the kernel command line, but maybe there's no way to avoid that
> since much/most? userspace treat "unknown" connector status as
> disconnected so many will have to force the connector to "connected"
> anyway. At least I don't know any way to permanetly force the connector
> status other than using video=.

You can do it through sysfs as well, in .../status

Maxime

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