linux-kernel - Re: [PATCH v1 00/35] drm: Analog TV Improvements

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Date:   Mon, 8 Aug 2022 15:03:42 +0200
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Maxime Ripard <maxime@...no.tech>,
        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>,
        Maxime Ripard <mripard@...nel.org>
Cc:     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>,
        Noralf Trønnes <noralf@...nnes.org>
Subject: Re: [PATCH v1 00/35] drm: Analog TV Improvements



Den 29.07.2022 18.34, skrev Maxime Ripard:
> Hi,
> 
> Here's a series aiming at improving the command line named modes support,
> and more importantly how we deal with all the analog TV variants.
> 
> The named modes support were initially introduced to allow to specify the
> analog TV mode to be used.
> 
> However, this was causing multiple issues:
> 
>   * The mode name parsed on the command line was passed directly to the
>     driver, which had to figure out which mode it was suppose to match;
> 
>   * Figuring that out wasn't really easy, since the video= argument or what
>     the userspace might not even have a name in the first place, but
>     instead could have passed a mode with the same timings;
> 
>   * The fallback to matching on the timings was mostly working as long as
>     we were supporting one 525 lines (most likely NSTC) and one 625 lines
>     (PAL), but couldn't differentiate between two modes with the same
>     timings (NTSC vs PAL-M vs NSTC-J for example); 
> 
>   * There was also some overlap with the tv mode property registered by 
>     drm_mode_create_tv_properties(), but named modes weren't interacting
>     with that property at all.
> 
>   * Even though that property was generic, its possible values were
>     specific to each drivers, which made some generic support difficult.
> 
> Thus, I chose to tackle in multiple steps:
> 
>   * A new TV norm property was introduced, with generic values, each driver
>     reporting through a bitmask what standard it supports to the userspace;
> 
>   * This option was added to the command line parsing code to be able to
>     specify it on the kernel command line, and new atomic_check and reset
>     helpers were created to integrate properly into atomic KMS;
> 
>   * The named mode parsing code is now creating a proper display mode for
>     the given named mode, and the TV standard will thus be part of the
>     connector state;
> 
>   * Two drivers were converted and tested for now (vc4 and sun4i), with
>     some backward compatibility code to translate the old TV mode to the
>     new TV mode;
> 
> Unit tests were created along the way. Nouveau, ch7006 and gud are
> currently broken for now since I expect that work to be reworked fairly
> significantly. I'm also not entirely sure about how to migrate GUD to the
> new property.
> 

I have looked at gud and I think the future proof solution is to add a
new TV_NORM property to the GUD protocol and add backwards compatibility
for the GUD_TV_MODE property (just for the modes that Raspberry Pi
supports since the gadget driver is out of tree). I don't bother
supporting the tv.mode property in userspace (I haven't seen anything
that uses the property).

I have written up most of the host driver changes but I have to do the
gadget side as well to make sure it works. I'll post some patches when
I'm done. In hindsight I should have used a bitmask for the TV standards
in the first place ;)

Noralf.