[RFC] drm/lcdc: add TI LCD Controller DRM driver

[Thierry Reding]

On Mon, Dec 17, 2012 at 10:36:10AM -0600, Rob Clark wrote:
> On Mon, Dec 17, 2012 at 9:26 AM, Sekhar Nori <nori.sekhar at gmail.com> wrote:
> > Hi Rob,
> >
> >
> > On Monday, December 17, 2012, Rob Clark wrote:
> >>
> >> On Mon, Dec 17, 2012 at 8:39 AM, Rob Clark <robdclark at gmail.com> wrote:
> >> >> I'm not very enthusiastic about adding ti-lcdc specific panel/chip
> >> >> drivers. It's not really a big deal if it's only kernel code, but you
> >> >> add device-tree bindings also, which is an external API that you need
> >> >> to
> >> >> support after adding it.
> >> >>
> >> >> I'd rather see the energy put to common display framework, and get this
> >> >> whole panel/chip driver issue solved in a generic manner.
> >> >
> >> > yeah, I was expecting to migrate to CDF once it exists, but needed
> >> > something for now.  I'm using the exercise to get my thoughts straight
> >> > on how CDF should fit into KMS.  (One thing I plan to add support for
> >> > is an i2c connected hdmi encoder.. which looks like it would fit well
> >> > in drivers/gpu/drm/i2c.. so the drm encoder-slave stuff might be the
> >> > way.)
> >> >
> >> > If you have any suggestions on the DT bindings, I'd like to hear 'em.
> >>
> >> btw, a little bit of-topic, but speaking of DT...
> >>
> >> Anybody have any clue about how backlight devices are supposed to work
> >> in this brave new DT world?
> >
> >
> > See Runtime interpreted power sequences here:
> >  http://lkml.indiana.edu/hypermail/linux/kernel/1208.2/00029.html
> >
> > It is an attempt to address this need.
> 
> hmm, I'm not really sure that is what is needed..  or rather, it might
> perhaps make sense to have a generic backlight driver implementation
> that could be used where appropriate, but I'm a bit suspicious about
> that trying to cover absolutely everything.
> 
> >From the drm/display driver we don't even want to care how the
> backlight is implemented.  You could have (just making something up
> hypothetically) a backlight controlled via a uart or some sort of
> other crazy magic.. and eventually the generic interpreter gets out of
> hand.
> 
> Really I think we just want a way to retrieve a 'struct
> backlight_device *' that is created somewhere else.  We don't care how
> that backlight driver is implemented.  I don't think we want an
> interpreter.. we want a way to lookup backlight device by name or
> phandle or something like that.

I posted a patch for this a while back. It adds a new function called
of_find_backlight_by_node() that does exactly that. The way it is
supposed to be used is somewhat like this:

	panel {
		backlight = <&backlight>;
	};

	backlight: backlight {
		...
	};

Then look up the phandle in the panel/DRM driver and call the new
function on the corresponding struct device_node *.

The patch went into 3.8-rc1.

And by the way, the future of the power-sequences series isn't very
clear. It was initially developed to allow the DT to contain power
sequencing for panels as part of the pwm-backlight driver, but that
idea was more or less killed by the CDF. The latest I know of is that
they could still be used as part of CDF to implement the actual power
sequences for drivers but not use their DT representation because
several people were unhappy about it.

Thierry
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