linux-kernel - Re: [PATCH v1 04/35] drm/modes: Introduce 480i and 576i modes

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Date:   Fri, 12 Aug 2022 15:18:58 +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>,
        Maxime Ripard <mripard@...nel.org>,
        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 04/35] drm/modes: Introduce 480i and 576i modes

Hi Maxime,

Thanks for your patch!

On Fri, Jul 29, 2022 at 6:35 PM Maxime Ripard <maxime@...no.tech> wrote:
> Multiple drivers (meson, vc4) define the analog TV 525-lines and 625-lines
> modes in the drivers.

Nit: strictly speaking these are not analog modes, but the digital
variants (ITU-R BT.656 and DVD-Video D1) of NTSC and PAL, using a
13.5 MHz sampling frequency for pixels.

In analog modes, the only discrete values are the number of lines, and
the frame/field rate (fixing the horizontal sync rate when combined).

The number of (in)visible pixels per line depends on the available
bandwidth.  In a digital variant (which is anything generated by a
digital computer system), the latter depends on the pixel clock, which
can wildly differ from the 13.5 MHz used in the BT.656 standard. (e.g.
Amiga uses 7.09/14.19/28.38 MHz (PAL) or 7.16/14.32/28.64 MHz (NTSC)).

So I think we probably need some way to generate a PAL/NTSC-compatible
mode based not only on resolution, but also on pixel clock.

>
> Since those modes are fairly standards, and that we'll need to use them in
> more places in the future, let's move the meson definition into the
> framework.
>
> The meson one was chosen because vc4's isn't accurate and doesn't amount to
> 525 and 625 lines.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -48,6 +48,24 @@
>
>  #include "drm_crtc_internal.h"
>
> +const struct drm_display_mode drm_mode_480i = {
> +       DRM_MODE("720x480i", DRM_MODE_TYPE_DRIVER, 13500,
> +                720, 739, 801, 858, 0,
> +                480, 488, 494, 525, 0,
> +                DRM_MODE_FLAG_INTERLACE),
> +       .picture_aspect_ratio = HDMI_PICTURE_ASPECT_4_3,
> +};
> +EXPORT_SYMBOL_GPL(drm_mode_480i);
> +
> +const struct drm_display_mode drm_mode_576i = {
> +       DRM_MODE("720x576i", DRM_MODE_TYPE_DRIVER, 13500,
> +                720, 732, 795, 864, 0,
> +                576, 580, 586, 625, 0,
> +                DRM_MODE_FLAG_INTERLACE),
> +       .picture_aspect_ratio = HDMI_PICTURE_ASPECT_4_3,
> +};
> +EXPORT_SYMBOL_GPL(drm_mode_576i);
> +
>  /**

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