linux-kernel - Re: [PATCH v2 10/41] drm/modes: Add a function to generate analog display modes

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Message-ID: <CAMuHMdWq3aOO4-2AReDeaC2VBJb=QJF2dTMZP=DGmwCg6ZOffA@mail.gmail.com>
Date:   Wed, 31 Aug 2022 10:14:28 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Mateusz Kwiatkowski <kfyatek@...il.com>
Cc:     Maxime Ripard <maxime@...no.tech>,
        Maxime Ripard <mripard@...nel.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Lyude Paul <lyude@...hat.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Karol Herbst <kherbst@...hat.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        Emma Anholt <emma@...olt.net>, Daniel Vetter <daniel@...ll.ch>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Phil Elwell <phil@...pberrypi.com>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Dom Cobley <dom@...pberrypi.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nouveau Dev <nouveau@...ts.freedesktop.org>,
        linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH v2 10/41] drm/modes: Add a function to generate analog
 display modes

Hi Mateusz,

On Wed, Aug 31, 2022 at 3:44 AM Mateusz Kwiatkowski <kfyatek@...il.com> wrote:
> Wow. That's an enormous amount of effort put into this patch.
>
> But I'm tempted to say that this is actually overengineered quite a bit :D
> Considering that there's no way to access all these calculations from user
> space, and I can't imagine anybody using anything else than those standard
> 480i/576i (and maybe 240p/288p) modes at 13.5 MHz any time soon... I'm not
> sure if we actually need all this.

We'll need it when we get an Amiga DRM driver, which will use
7/14/28 MHz pixel clocks.

> But anyway, I'm not the maintainer of this subsystem, so I'm not the one to
> decide.
>
> > +enum drm_mode_analog {
> > +    DRM_MODE_ANALOG_NTSC,
> > +    DRM_MODE_ANALOG_PAL,
> > +};
>
> Using "NTSC" and "PAL" to describe the 50Hz and 60Hz analog TV modes is common,
> but strictly speaking a misnomer. Those are color encoding systems, and your
> patchset fully supports lesser used, but standard encodings for those (e.g.
> PAL-M for 60Hz and SECAM for 50Hz). I'd propose switching to some more neutral
> naming scheme. Some ideas:
>
> - DRM_MODE_ANALOG_60_HZ / DRM_MODE_ANALOG_50_HZ (after standard refresh rate)
> - DRM_MODE_ANALOG_525_LINES / DRM_MODE_ANALOG_625_LINES (after standard line
>   count)

IMHO these are bad names, as e.g. VGA640x480@60 is also analog, using
60 Hz and 525 lines.  Add "TV" to the name?

> - DRM_MODE_ANALOG_JM / DRM_MODE_ANALOG_BDGHIKLN (after corresponding ITU System
>   Letter Designations)

Or DRM_MODE_ITU_*?
But given the long list of letters, this looks fragile to me.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds