Den 17.08.2022 13.46, skrev Maxime Ripard:

On Tue, Aug 16, 2022 at 09:35:24PM +0200, Noralf Trønnes wrote:

quoted

Den 16.08.2022 11.49, skrev Maxime Ripard:

quoted

On Tue, Aug 16, 2022 at 11:42:20AM +0200, Noralf Trønnes wrote:

quoted

Den 16.08.2022 10.26, skrev Maxime Ripard:

quoted

Hi,

On Mon, Aug 08, 2022 at 02:44:56PM +0200, Noralf Trønnes wrote:

quoted

Den 29.07.2022 18.34, skrev Maxime Ripard:

quoted

The TV mode property has been around for a while now to select and get the
current TV mode output on an analog TV connector.

Despite that property name being generic, its content isn't and has been
driver-specific which makes it hard to build any generic behaviour on top
of it, both in kernel and user-space.

Let's create a new bitmask tv norm property, that can contain any of the
analog TV standards currently supported by kernel drivers. Each driver can
then pass in a bitmask of the modes it supports.

We'll then be able to phase out the older tv mode property.

Signed-off-by: Maxime Ripard <redacted>

Please also update Documentation/gpu/kms-properties.csv

Requirements for adding a new property is found in
Documentation/gpu/drm-kms.rst

I knew this was going to be raised at some point, so I'm glad it's that
early :)

I really don't know what to do there. If we stick by our usual rules,
then we can't have any of that work merged.

However, I think the status quo is not really satisfactory either.
Indeed, we have a property, that doesn't follow those requirements
either, with a driver-specific content, and that stands in the way of
fixes and further improvements at both the core framework and driver
levels.

So having that new property still seems like a net improvement at the
driver, framework and uAPI levels, even if it's not entirely following
the requirements we have in place.

Even more so since, realistically, those kind of interfaces will never
get any new development on the user-space side of things, it's
considered by everyone as legacy.

This also is something we need to support at some point if we want to
completely deprecate the fbdev drivers and provide decent alternatives
in KMS.

So yeah, strictly speaking, we would not qualify for our requirements
there. I still think we have a strong case for an exception though.

Which requirements would that be? The only one I can see is the
documentation and maybe an IGT test.

This is the one I had in mind
https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#open-source-userspace-requirements

Oh right, I had forgotten about that one.

One benefit of having a userspace implementation is that it increases
the chance of widespread adoption having a working implementation to
look at. I don't think the reason tv.mode is not used anywhere (that I
know of) is because the driver picks the enum values resulting in no
standard names.

It probably doesn't help, but it's not what I was implying.

quoted

It's a niche thing and way down on the todo list. nouveau and ch7006
has a tv_norm module parameter which certainly doesn't help in moving
people/projects over to the DRM property (downstream rpi also has it
now).

Yeah, the RPi version is part of the reason I started working on this.
We should also consider the named modes used by vc4 and sun4i. All these
ad-hoc solutions are limited and (I think) come from the fact that we
don't have a solution easy enough to use for drivers (and to discover).

nouveau, ch7006, i915 and vc4 are using the tv.mode property for
example, but sun4i and meson don't.

sun4i relies on named modes to reimplement TV modes, but meson doesn't
at all.

And then nouveau has that extra command line parameter to set it up at
boot time.

It doesn't really make much sense to me, when all drivers have very
similar needs, that none of them behave in the same way. And I think the
non-standard property is partly to blame for this, since without some
generic content we can't share code.

This is what this series is about: every driver having similar
capabilities and as trivially as possible.

quoted

mpv[1] is a commandline media player that after a quick look might be a
candidate for implementing the property without too much effort.

Kodi might be another one. I can try to hack something around, but I'm
really skeptical about whether a PR would be merged or not.

You can ask first before wasting time ofc.

But this baffles me, if you don't think projects like Kodi which is TV
centered want this, what kind of projects do you think want to use this
property?

quoted

How do you test the property? I've used modetest but I can only change
to a tv.mode that matches the current display mode. I can't switch from
ntsc to pal for instance.

Yep, if you want to change from PAL to NTSC, it will require a new mode.

So userspace has to check tv.mode first and then create a display mode
the driver will accept if switching to a different display mode is
necessary? In other words, userspace can't discover from the kernel
which display modes a certain tv.mode/norm provides before it is
selected? If so, maybe libdrm should have some function(s) to deal with
switching between modes that require a different display mode since
knowledge about which display modes a tv.mode supports is needed before
hand.

Noralf.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel