linux-kernel - Re: [PATCH v1 05/35] drm/connector: Add TV standard property

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Message-ID: <CAMuHMdUNYErf4PJLbSFFdB1EhvzbscqxHE74FnsjYQXLy8DLZA@mail.gmail.com>
Date:   Fri, 19 Aug 2022 11:35:42 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Maxime Ripard <maxime@...no.tech>
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>,
        Noralf Trønnes <noralf@...nnes.org>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-sunxi@...ts.linux.dev,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Phil Elwell <phil@...pberrypi.com>,
        Mateusz Kwiatkowski <kfyatek+publicgit@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Dom Cobley <dom@...pberrypi.com>
Subject: Re: [PATCH v1 05/35] drm/connector: Add TV standard property

Hi Maxime,

On Thu, Aug 18, 2022 at 5:34 PM Maxime Ripard <maxime@...no.tech> wrote:
> On Thu, Aug 18, 2022 at 05:20:42PM +0200, Geert Uytterhoeven wrote:
> > On Thu, Aug 18, 2022 at 4:54 PM Maxime Ripard <maxime@...no.tech> wrote:
> > > On Wed, Aug 17, 2022 at 04:04:24PM +0200, Geert Uytterhoeven wrote:
> > > > On Wed, Aug 17, 2022 at 3:19 PM Maxime Ripard <maxime@...no.tech> wrote:
> > > > > On Wed, Aug 17, 2022 at 03:05:52PM +0200, Geert Uytterhoeven wrote:
> > > > > > On Wed, Aug 17, 2022 at 1:15 PM Maxime Ripard <maxime@...no.tech> wrote:
> > > > > > > On Wed, Aug 17, 2022 at 10:35:07AM +0200, Geert Uytterhoeven wrote:
> > > > > > > > On Wed, Aug 17, 2022 at 9:47 AM Maxime Ripard <maxime@...no.tech> wrote:
> > > > > > > > > On Wed, Aug 17, 2022 at 09:31:18AM +0200, Geert Uytterhoeven wrote:
> > > > > > > > > > On Tue, Aug 16, 2022 at 5:50 PM Maxime Ripard <maxime@...no.tech> wrote:
> > > > > > > > > > > On Tue, Aug 16, 2022 at 04:43:44PM +0200, Geert Uytterhoeven wrote:
> > > > > > > > > > > > > > > > Either you have to add them here (e.g. "hd720p50" and "hd720p60"), or
> > > > > > > > > > > > > > > > handle them through "@<refresh>".  The latter would impact "[PATCH v1
> > > > > > > > > > > > > > > > 09/35] drm/modes: Move named modes parsing to a separate function", as
> > > > > > > > > > > > > > > > currently a named mode and a refresh rate can't be specified both.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > I think the former would make more sense. It simplifies a bit the
> > > > > > > > > > > > > > > parser, and we're going to use a named mode anyway.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > As "[PATCH v1 34/35] drm/modes: Introduce the tv_mode property as a
> > > > > > > > > > > > > > > > command-line option" uses a separate "tv_mode" option, and not the main
> > > > > > > > > > > > > > > > mode name, I think you want to add them here.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > It's a separate story I think, we could have a named mode hd720p50,
> > > > > > > > > > > > > > > which would be equivalent to 1280x720,tv_mode=hd720p
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > So where's the field rate in "1280x720,tv_mode=hd720p"?
> > > > > > > > > > > > >
> > > > > > > > > > > > > Yeah, sorry I meant 1280x720@50,tv_mode=hd720p
> > > > > > > > > > > >
> > > > > > > > > > > > Above you said "I think the former would make more sense", so that
> > > > > > > > > > > > should be "1280x720,tv_mode=hd720p50"?
> > > > > > > > > > >
> > > > > > > > > > > No, 720p at 50Hz would be either hd720p50 or 1280x720@50,tv_mode=hd720p
> > > > > > > > > > > and 60Hz would be hd720p60 or 1280x720@60,tv_mode=hd720p
> > > > > > > > > >
> > > > > > > > > > I disagree: hd720p50 and hd720p60 are different TV modes.
> > > > > > > > >
> > > > > > > > > I agree, and I don't see how that command-line doesn't express that?
> > > > > > > >
> > > > > > > > Oh, I see what you mean: yes, it expresses that.
> > > > > > > > But it is inconsistent with the NTSC/PAL/SECAM/hd{480,576}[ip] modes,
> > > > > > > > where the TV mode specifies both number of lines and frame rate.
> > > > > > >
> > > > > > > Only if we're using a named mode, and naming is hard :)
> > > > > >
> > > > > > That's not true: "640x480,tv_mode=PAL-N" would give me a mode with
> > > > > > 625 lines and 25 frames/s, "640x480,tv_mode=PAL-M" would give me a
> > > > > > mode with 525 lines and 30 frames/s.
> > > > >
> > > > > In that series, "640x480,tv_mode=PAL-N" would be rejected as invalid:
> > > > >
> > > > > https://lore.kernel.org/dri-devel/20220728-rpi-analog-tv-properties-v1-14-3d53ae722097@cerno.tech/
> > > >
> > > > It would become supported once the ideas from thread "[PATCH v1 04/35]
> > > > drm/modes: Introduce 480i and 576i modes" are implemented...
> > >
> > > Indeed, but I'm still not sure what your concern is here.
> > > "640x480,tv_mode=PAL-N" and "640x480,tv_mode=PAL-M" are both fairly
> > > obvious.
> > >
> > > You were initially saying that you had concern over the inconsistency of
> > > NTSC/PAL/SECAM where the TV mode would specify a number of lines and
> > > frame rate, but hd720p50 also specifies a number of line and frame rate?
> >
> > My concern is that you want to call the TV mode "hd720p", which
> > does not dictate the frame rate.
> > I would like to have both "720p50" and "720p60", as they do dictate
> > the frame rate, like all the non-hd modes.
>
> But they don't?
>
> The refresh rate is part of the drm_display_mode, whereas that property
> is metadata and entirely separate from the display mode.
>
> You can even change it without changing the mode at all

Yes, the refresh rate is part of drm_display_mode.  Vdisplay also
is, but that doesn't mean you can set it to e.g. 700 when using
"tv_mode=PAL-B". Some (combination of) parameters in drm_display_mode
are dictated by the tv_mode.

Perhaps the meaning of "tv_mode" should be clarified? What does it
really mean, and what parameters does it (not) constrain?

For e.g. "PAL-B", I know it's a mode with 625 lines and 30 frames/s
(60 fields/s).
For "hd720p" I know it is an analog mode with 750 lines, but it's still
ambiguous, as I don't know if it is the variant with 60 or 50 frames/s.

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