linux-kernel - Re: [PATCH v5] video: add OpenCores VGA/LCD framebuffer driver

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Message-ID: <20140113111508.GB30877@chokladfabriken.org>
Date:	Mon, 13 Jan 2014 13:15:10 +0200
From:	Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Tomi Valkeinen <tomi.valkeinen@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
Subject: Re: [PATCH v5] video: add OpenCores VGA/LCD framebuffer driver

On Mon, Jan 13, 2014 at 11:54:30AM +0100, Geert Uytterhoeven wrote:
> On Mon, Jan 13, 2014 at 11:43 AM, Tomi Valkeinen <tomi.valkeinen@...com> wrote:
> > On 2014-01-13 12:20, Stefan Kristiansson wrote:
OB> >> The VGA/LCD in the subject comes from the name of the core,
> >> the core itself presents a "vga-type" interface, but it can basically
> >> be hooked up to any type of display (with a bit of glue-logic in some cases).
> >>
> >> That said - the reason why I went for the mode_options solution in the
> >> first place, is that when I initially wrote this driver
> >> (>2 years ago, time flies...) the display-timing device-tree bindings weren't
> >> invented yet, so it seemed like the most viable option without coming up
> >> with custom device-tree bindings.
> >>
> >> It's completely possible that this design choice should be revised now,
> >> and I wouldn't mind converting this driver to make use of the display-timing
> >> dt properties if you think that's a good idea?
> >
> > I don't have a strong opinion on this. It looks to me that even if the
> > current driver is merged, it would be easy to add device tree
> > display-timing later, and still keep full backward compatibility.
> >
> > Then again, you already have DT support in the driver, and if it's clear
> > that the DT based videomode selection is better, then I'd just go
> > straight to that one without intermediate steps.
> 
> With a VGA connector, it's handy to be able to specify the video mode on
> the kernel command line, instead of having to put it in the DT.
> 
> With hardwired LCDs with fixed timing, it's different.
> 

Right, so either way, we probably want to keep the kernel command line option.
I think the main motivation for switching to the dt based video mode
selection at this stage would be to avoid having the kernel command line
option around, so I think I would like to move forward with the current
implementation with the possibility to improve it with display-timing bindings
later on.

Stefan
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