Re: [PATCH v4 11/30] drm/modes: Add a function to generate analog display modes

From: Maxime Ripard <maxime@cerno.tech>
To: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Jernej Skrabec <jernej.skrabec@gmail.com>,
	Chen-Yu Tsai <wens@csie.org>, Karol Herbst <kherbst@redhat.com>,
	Samuel Holland <samuel@sholland.org>,
	Lyude Paul <lyude@redhat.com>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	Daniel Vetter <daniel@ffwll.ch>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Emma Anholt <emma@anholt.net>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Ben Skeggs <bskeggs@redhat.com>, David Airlie <airlied@linux.ie>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	linux-arm-kernel@lists.infradead.org,
	dri-devel@lists.freedesktop.org,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	intel-gfx@lists.freedesktop.org, linux-sunxi@lists.linux.dev,
	Hans de Goede <hdegoede@redhat.com>,
	nouveau@lists.freedesktop.org,
	Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>,
	Dave Stevenson <dave.stevenson@raspberrypi.com>,
	linux-kernel@vger.kernel.org, Dom Cobley <dom@raspberrypi.com>,
	Phil Elwell <phil@raspberrypi.com>
Subject: Re: [PATCH v4 11/30] drm/modes: Add a function to generate analog display modes
Date: Thu, 13 Oct 2022 10:36:38 +0200	[thread overview]
Message-ID: <20221013083638.kloiaxervnhii7ew@houat> (raw)
In-Reply-To: <0aa690b8-988a-878f-4d4f-d391295bc591@tronnes.org>

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Hi Noralf,

On Sat, Oct 01, 2022 at 02:52:06PM +0200, Noralf Trønnes wrote:
> Den 29.09.2022 18.31, skrev Maxime Ripard:
> > Multiple drivers (meson, vc4, sun4i) define analog TV 525-lines and
> > 625-lines modes in their drivers.
> > 
> > Since those modes are fairly standard, and that we'll need to use them
> > in more places in the future, it makes sense to move their definition
> > into the core framework.
> > 
> > However, analog display usually have fairly loose timings requirements,
> > the only discrete parameters being the total number of lines and pixel
> > clock frequency. Thus, we created a function that will create a display
> > mode from the standard, the pixel frequency and the active area.
> > 
> > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > 
> > ---
> > 
> > Changes in v4:
> > - Reworded the line length check comment
> > - Switch to HZ_PER_KHZ in tests
> > - Use previous timing to fill our mode
> > - Move the number of lines check earlier
> > ---
> >  drivers/gpu/drm/drm_modes.c            | 474 +++++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/tests/Makefile         |   1 +
> >  drivers/gpu/drm/tests/drm_modes_test.c | 144 ++++++++++
> >  include/drm/drm_modes.h                |  17 ++
> >  4 files changed, 636 insertions(+)
> > 
> 
> I haven't followed the discussion on this patch, but it seems rather
> excessive to add over 600 lines of code (including tests) to add 2 fixed
> modes. And it's very difficult to see from the code what the actual
> display mode timings really are, which would be useful for other
> developers down the road wanting to use them.
> 
> Why not just hardcode the modes?

Yeah, I have kind of the same feeling tbh, but it was asked back on the
v1 to ease the transition of old fbdev drivers, since they will need
such a function:
https://lore.kernel.org/dri-devel/CAMuHMdUrwzPYjA0wdR7ADj5Ov6+m03JbnY8fBYzRYyWDuNm5=g@mail.gmail.com/

Maxime

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