linux-kernel - Re: [PATCH v1 09/35] drm/modes: Move named modes parsing to a separate function

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Date:   Tue, 16 Aug 2022 15:46:24 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
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 09/35] drm/modes: Move named modes parsing to a
 separate function

On Fri, Aug 12, 2022 at 03:27:17PM +0200, Geert Uytterhoeven wrote:
> Hi Maxime,
> 
> On Fri, Jul 29, 2022 at 6:36 PM Maxime Ripard <maxime@...no.tech> wrote:
> > The current construction of the named mode parsing doesn't allow to extend
> > it easily. Let's move it to a separate function so we can add more
> > parameters and modes.
> >
> > Signed-off-by: Maxime Ripard <maxime@...no.tech>
> 
> Thanks for your patch, which looks similar to my "[PATCH v2 2/5]
> drm/modes: Extract drm_mode_parse_cmdline_named_mode()"
> (https://lore.kernel.org/dri-devel/1371554419ae63cb54c2a377db0c1016fcf200bb.1657788997.git.geert@linux-m68k.org
> ;-)

Indeed, I forgot about that one, sorry :/

I think I'd still prefer to have the check for refresh + named mode
outside of the function, since I see them as an "integration" issue, not
a parsing one.

It's not the named mode parsing that fails, but the fact that we both
have a valid refresh and a valid named mode.

> 
> > --- a/drivers/gpu/drm/drm_modes.c
> > +++ b/drivers/gpu/drm/drm_modes.c
> > @@ -1773,6 +1773,28 @@ static const char * const drm_named_modes_whitelist[] = {
> >         "PAL",
> >  };
> >
> > +static bool drm_mode_parse_cmdline_named_mode(const char *name,
> > +                                             unsigned int name_end,
> > +                                             struct drm_cmdline_mode *cmdline_mode)
> > +{
> > +       unsigned int i;
> > +
> > +       for (i = 0; i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
> > +               int ret;
> > +
> > +               ret = str_has_prefix(name, drm_named_modes_whitelist[i]);
> > +               if (ret != name_end)
> > +                       continue;
> > +
> > +               strcpy(cmdline_mode->name, drm_named_modes_whitelist[i]);
> > +               cmdline_mode->specified = true;
> > +
> > +               return true;
> > +       }
> > +
> > +       return false;
> 
> What's the point in returning a value, if it is never checked?
> Just make this function return void?

Yeah, it's something I went back and forth to between the dev, and it's
an artifact.

I'll drop that patch, take your version and move the refresh check to
drm_mode_parse_command_line_for_connector if that's alright for you?

Maxime

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