Message-ID: <20220909094647.aahohiwtwbbeyzj3@houat>
Date:   Fri, 9 Sep 2022 11:46:47 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Mateusz Kwiatkowski <kfyatek@...il.com>
Cc:     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-kernel@...ts.infradead.org,
        Phil Elwell <phil@...pberrypi.com>,
        intel-gfx@...ts.freedesktop.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        dri-devel@...ts.freedesktop.org, Dom Cobley <dom@...pberrypi.com>,
        linux-kernel@...r.kernel.org, nouveau@...ts.freedesktop.org,
        linux-sunxi@...ts.linux.dev,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v2 09/41] drm/connector: Add TV standard property

On Wed, Sep 07, 2022 at 09:52:09PM +0200, Mateusz Kwiatkowski wrote:
> W dniu 7.09.2022 o 14:10, Maxime Ripard pisze:
> > Hi,
> >
> > On Fri, Sep 02, 2022 at 12:00:33AM +0200, Mateusz Kwiatkowski wrote:
> >> W dniu 29.08.2022 o 15:11, Maxime Ripard pisze:
> >>> 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.
> >>
> >> This is not a bitmask property anymore, you've just changed it to an enum.
> >> The commit message is now misleading.
> >>
> >>> +static const struct drm_prop_enum_list drm_tv_mode_enum_list[] = {
> >>> +    { DRM_MODE_TV_MODE_NTSC_443, "NTSC-443" },
> >>> +    { DRM_MODE_TV_MODE_NTSC_J, "NTSC-J" },
> >>> +    { DRM_MODE_TV_MODE_NTSC_M, "NTSC-M" },
> >>> +    { DRM_MODE_TV_MODE_PAL_60, "PAL-60" },
> >>> +    { DRM_MODE_TV_MODE_PAL_B, "PAL-B" },
> >>> +    { DRM_MODE_TV_MODE_PAL_D, "PAL-D" },
> >>> +    { DRM_MODE_TV_MODE_PAL_G, "PAL-G" },
> >>> +    { DRM_MODE_TV_MODE_PAL_H, "PAL-H" },
> >>> +    { DRM_MODE_TV_MODE_PAL_I, "PAL-I" },
> >>> +    { DRM_MODE_TV_MODE_PAL_M, "PAL-M" },
> >>> +    { DRM_MODE_TV_MODE_PAL_N, "PAL-N" },
> >>> +    { DRM_MODE_TV_MODE_PAL_NC, "PAL-Nc" },
> >>> +    { DRM_MODE_TV_MODE_SECAM_60, "SECAM-60" },
> >>> +    { DRM_MODE_TV_MODE_SECAM_B, "SECAM-B" },
> >>> +    { DRM_MODE_TV_MODE_SECAM_D, "SECAM-D" },
> >>> +    { DRM_MODE_TV_MODE_SECAM_G, "SECAM-G" },
> >>> +    { DRM_MODE_TV_MODE_SECAM_K, "SECAM-K" },
> >>> +    { DRM_MODE_TV_MODE_SECAM_K1, "SECAM-K1" },
> >>> +    { DRM_MODE_TV_MODE_SECAM_L, "SECAM-L" },
> >>> +};
> >>
> >> I did not comment on it the last time, but this list looks a little bit random.
> >>
> >> Compared to the standards defined by V4L2, you also define SECAM-60 (a good
> >> thing to define, because why not), but don't define PAL-B1, PAL-D1, PAL-K,
> >> SECAM-H, SECAM-LC (whatever that is - probably just another name for SECAM-L,
> >> see my comment about PAL-Nc below), or NTSC-M-KR (a Korean variant of NTSC).
> >>
> >> Like I mentioned previously, I'm personally not a fan of including all those
> >> CCIR/ITU system variants, as they don't mean any difference to the output unless
> >> there is an RF modulator involved. But I get it that they have already been used
> >> and regressing probably wouldn't be a very good idea. But in that case keeping
> >> it consistent with the set of values used by V4L2 would be wise, I think.
> >
> > Ack. What would be the list of standards we'd absolutely need? NSTC-M,
> > NTSC-J, PAL-60, PAL-B, PAL-M, SECAM-60 and SECAM-B?
> 
> The "essential list" IMO is NTSC, NTSC-J, NTSC-443, PAL, PAL-M, PAL-N and SECAM.
> Note that:
> 
> - I intentionally propose "NTSC", "PAL" and "SECAM" without an ITU system
>   designation. If we only consider composite signals, there's no difference
>   between e.g. PAL-B, PAL-D and PAL-I, so it's better to label it as a generic
>   mode, IMO.
> 
>   * PAL-M and PAL-N are different, because those unique color encodings were
>     only ever used with Systems M and N, respectively.
> 
>   * NTSC-J is also different, because "System J" doesn't exist anywhere in ITU
>     documents. Japan technically uses System M with a non-standard black level.
>     But "NTSC-J" stuck as a universally recognized name for that variant.
> 
> - I intentionally did not list PAL-60 or SECAM-60. TBH... PAL-60 is just
>   regular PAL paired with 480i60 modeline. Most if not all displays that
>   accept PAL-60 input will just label it as "PAL". If we are not introducing
>   strict modeline validation, then maybe separating PAL and PAL-60 isn't really
>   necessary? Same goes for SECAM vs. SECAM-60.
>  
>   ...and same goes for NTSC vs. NTSC-50 a.k.a NTSC-N, which is a very exotic
>   mode, but known to exist at least in the Atari ST world, see also:
>   https://en.wikipedia.org/wiki/NTSC#NTSC-N/NTSC50
> 
> Combining PAL and PAL-60 into a single setting would complicate the vc4 driver
> a little bit, though, as the registers need to be set up differently for those.
> 
> My feelings about the PAL-60 issue are not that strong, though. Merging PAL
> and PAL-60 in this context is just a loose suggestion, I won't even try to
> argue if you disagree.

Ack

> >>> +/**
> >>> + * drm_mode_create_tv_properties - create TV specific connector properties
> >>> + * @dev: DRM device
> >>> + * @supported_tv_modes: Bitmask of TV modes supported (See DRM_MODE_TV_MODE_*)
> >>> +
> >>> + * Called by a driver's TV initialization routine, this function creates
> >>> + * the TV specific connector properties for a given device.  Caller is
> >>> + * responsible for allocating a list of format names and passing them to
> >>> + * this routine.
> >>> + *
> >>> + * Returns:
> >>> + * 0 on success or a negative error code on failure.
> >>> + */
> >>> +int drm_mode_create_tv_properties(struct drm_device *dev,
> >>> +                  unsigned int supported_tv_modes)
> >>
> >> supported_tv_modes is supposed to be a bitmask of BIT(DRM_MODE_TV_MODE_*)
> >> (or (1<<DRM_MODE_TV_MODE_*)) rather than DRM_MODE_TV_MODE_* directly, but this
> >> is not said explicitly anywhere in this doc comment.
> >
> > The argument doc mentions that it's a "Bitmask of TV modes supported
> > (See DRM_MODE_TV_MODE_*)", how would you improve it?
> 
> Maybe something like "Bitwise OR of BIT(DRM_MODE_TV_MODE_*) values"? Or maybe
> just add a little usage example?

This is the way we're usually documenting it in DRM:
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_plane.c#L357
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_crtc.c#L861
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_blend.c#L546

So I'd rather keep it consistent

Maxime

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