linux-kernel - Re: [PATCH v6 16/23] drm/probe-helper: Provide a TV get

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Date:   Mon, 7 Nov 2022 11:21:26 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Noralf Trønnes <noralf@...nnes.org>
Cc:     Karol Herbst <kherbst@...hat.com>, Emma Anholt <emma@...olt.net>,
        Ben Skeggs <bskeggs@...hat.com>, Chen-Yu Tsai <wens@...e.org>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Samuel Holland <samuel@...lland.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Lyude Paul <lyude@...hat.com>, linux-sunxi@...ts.linux.dev,
        intel-gfx@...ts.freedesktop.org,
        Phil Elwell <phil@...pberrypi.com>,
        linux-arm-kernel@...ts.infradead.org,
        nouveau@...ts.freedesktop.org, Hans de Goede <hdegoede@...hat.com>,
        Dom Cobley <dom@...pberrypi.com>,
        Mateusz Kwiatkowski <kfyatek+publicgit@...il.com>,
        dri-devel@...ts.freedesktop.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v6 16/23] drm/probe-helper: Provide a TV get_modes helper

Hi Noralf,

I'll leave aside your comments on the code, since we'll use your implementation.

On Sun, Nov 06, 2022 at 05:33:48PM +0100, Noralf Trønnes wrote:
> Den 26.10.2022 17.33, skrev maxime@...no.tech:
> > +
> > +	if (cmdline->tv_mode_specified)
> > +		default_mode = cmdline->tv_mode;
> 
> I realised that we don't verify tv_mode coming from the command line,
> not here and not in the reset helper. Should we do that? A driver should
> be programmed defensively to handle an illegal/unsupported value, but it
> doesn't feel right to allow an illegal enum value coming through the
> core/helpers.

I don't think we can end up with an invalid value here if it's been
specified.

We parse the command line through drm_mode_parse_tv_mode() (introduced
in patch 13 "drm/modes: Introduce the tv_mode property as a command-line
option") that will pick the tv mode part of the command line, and call
drm_get_tv_mode_from_name() using it.

drm_get_tv_mode_from_name() will return a EINVAL if it's not a value we
expect, and mode->tv_mode is only set on success. And AFAIK, there's no
other path that will set tv_mode.

Maxime

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