Re: [PATCH v5 2/7] drm/panel: simple: Add ability to override typical timing

From: Sam Ravnborg <sam@ravnborg.org>
To: Doug Anderson <dianders@chromium.org>
Cc: "Thierry Reding" <thierry.reding@gmail.com>,
	"Heiko Stuebner" <heiko@sntech.de>,
	"Sean Paul" <seanpaul@chromium.org>,
	devicetree@vger.kernel.org, "Rob Herring" <robh+dt@kernel.org>,
	"David Airlie" <airlied@linux.ie>,
	"Jeffy Chen" <jeffy.chen@rock-chips.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	"Boris Brezillon" <boris.brezillon@collabora.com>,
	"Laurent Pinchart" <laurent.pinchart@ideasonboard.com>,
	"Enric Balletbò" <enric.balletbo@collabora.com>,
	"Stéphane Marchesin" <marcheu@chromium.org>,
	"Ezequiel Garcia" <ezequiel@collabora.com>,
	"Matthias Kaehlcke" <mka@chromium.org>
Subject: Re: [PATCH v5 2/7] drm/panel: simple: Add ability to override typical timing
Date: Mon, 8 Jul 2019 19:50:08 +0200	[thread overview]
Message-ID: <20190708175007.GA3511@ravnborg.org> (raw)
In-Reply-To: <CAD=FV=V_wTD1xpkXRe-z2HsZ8QXKq7jmq8CsfhMnFxi-5XDJjw@mail.gmail.com>

Hi Dough.

On Mon, Jul 01, 2019 at 09:39:24AM -0700, Doug Anderson wrote:
> Hi,
> 
> On Sun, Jun 30, 2019 at 1:22 PM Sam Ravnborg <sam@ravnborg.org> wrote:
> >
> > > @@ -91,6 +92,8 @@ struct panel_simple {
> > >       struct i2c_adapter *ddc;
> > >
> > >       struct gpio_desc *enable_gpio;
> > > +
> > > +     struct drm_display_mode override_mode;
> > I fail to see where this poiter is assigned.
> 
> In panel_simple_parse_override_mode().  Specifically:
> 
> drm_display_mode_from_videomode(&vm, &panel->override_mode);

The above code-snippet is only called in the panel has specified display
timings using display_timings - it is not called when display_mode is
used.
So override_mode is only assigned in some cases and not all cases.
This needs to be fixed so we do not reference override_mode unless
it is set.

> 
> 
> > @@ -152,6 +162,44 @@ static int panel_simple_get_fixed_modes(struct panel_simple *panel)
> > >               num++;
> > >       }
> > >
> > > +     return num;
> > > +}
> > > +
> > > +static int panel_simple_get_non_edid_modes(struct panel_simple *panel)
> > > +{
> > > +     struct drm_connector *connector = panel->base.connector;
> > > +     struct drm_device *drm = panel->base.drm;
> > > +     struct drm_display_mode *mode;
> > > +     bool has_override = panel->override_mode.type;
> > This looks suspicious.
> > panel->override_mode.type is an unsigned int that may have a number of
> > bits set.
> > So the above code implicitly convert a .type != 0 to a true.
> > This can be expressed in a much more reader friendly way.
> 
> You would suggest that I add a boolean field to a structure to
> indicate whether an override mode is present?
A simple  bool has_override = panel->override_mode.type != 0;
would do the trick here.
Then there is no hidden conversion from int to a bool.

But as override_mode can be NULL something more needs to be done.

	Sam