linux-kernel - Re: [PATCH v2] video: simplefb: add mode parsing function

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Message-ID: <20130601051223.GB5189@quad.lixom.net>
Date:	Fri, 31 May 2013 22:12:23 -0700
From:	Olof Johansson <olof@...om.net>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>, Rob Clark <robclark@...il.com>,
	linux-fbdev@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rpi-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	gnurou@...il.com
Subject: Re: [PATCH v2] video: simplefb: add mode parsing function

On Mon, May 27, 2013 at 10:13:09PM -0600, Stephen Warren wrote:
> On 05/26/2013 09:53 PM, Alexandre Courbot wrote:
> > The naming scheme of simplefb's mode is precise enough to allow building
> > the mode structure from it instead of using a static list of modes. This
> > patch introduces a function that does this. In case exotic modes that
> > cannot be represented from their name alone are needed, the static list
> > of modes is still available as a backup.
> > 
> > It also changes the order in which colors are declared from MSB first to
> > the more standard LSB first.
> > 
> > Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> > ---
> > Changes from v1:
> > - amended documentation following Stephen's suggestion
> > - allow parsing of bitfields larger than 9 bits
> > - made it clear that the parsing order of bits is changed with respect
> >   to the original patch
> > 
> > Andrew, since this patch introduces a (small) change in the DT bindings,
> > could we try to merge it during the -rc cycle so we don't have to come
> > with a more complex solution in the future?
> 
> So, I think we shouldn't change the DT binding at all now. The original
> driver is now merged for 3.10, and I think it's far too late to take
> code that implements new features for 3.10. This means that we couldn't
> merge this patch until 3.11. However, by then, we shouldn't be changing
> the DT binding in incompatible ways. Olof has already published some
> U-Boot binaries that use the current binding, and on IRC indicated he'd
> prefer not to change the binding because of that.
> 
> As such, we should either:
> 
> a) Just add new entries into the format array that already exists in the
> driver. Given David's response, this might be simplest.

I think so too. Is this even needed? Do we have any users of the newer formats
or is it just someone trying to feature-creep this driver to make the "simple"
part of the name inaccurate? :)

> b) Extend the DT binding in a 100% backwards-compatible way, which would
> mean defaulting the bit-order to match the existing 1 format, and adding
> a new Boolean property to indicate that the format string is specified
> in the other order.

Or just add a new property that has higher priority for the newer format
strings, and make the driver use that if it exists, otherwise fall back.


-Olof
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