Re: [PATCH v3 07/10] drm: rcar-du: Skip LVDS1 output on Gen3 when using dual-link LVDS mode

From: Sam Ravnborg <sam@ravnborg.org>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: linux-renesas-soc@vger.kernel.org,
	Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
	Jacopo Mondi <jacopo+renesas@jmondi.org>,
	Kieran Bingham <kieran.bingham@ideasonboard.com>,
	dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v3 07/10] drm: rcar-du: Skip LVDS1 output on Gen3 when using dual-link LVDS mode
Date: Thu, 6 Jun 2019 11:29:59 +0200	[thread overview]
Message-ID: <20190606092959.GB17442@ravnborg.org> (raw)
In-Reply-To: <20190606075750.GE4931@pendragon.ideasonboard.com>

Hi Laurent.

> > > Gen3 is the newest generation :-) We thus use >= through the DU and LVDS
> > > drivers to prepare for support of Gen4, just in case.
> >
> > OK, but I guess we agree that the comment needs a small update them.
> > 
> > Actually I implicitly reads that it is only from Gen3 onwards that the
> > LVDS1 encoder can be used as a companion.
> > My initial understanding reading the comment was that this implmented a
> > workaround for Gen3 - but it is a workarounf for missing features in
> > older than Gen3.
> 
> I wouldn't say workaround, it just makes sure that we don't try to
> support LVDS dual-mode on older SoCs as the feature was added in Gen3
> hardware.
> 
> > So, assuming this is correct, when trying to specify a companion on
> > older then Gen3 should result in some kind of error/warning?
> > (Maybe it does).
> 
> The property is ignored in that case. I could add an error message, but
> I'm not sure I should, as we don't usually check that DT nodes don't
> contain any other property than the ones specified in the DT bindings
> (an automatic DT runtime validator based on the YAML bindings could be
> interesting ;-)).
Again, thanks for taking your time.
This clarifies it nicely.

	Sam