linux-kernel - Re: [PATCH 0/3] pwm-backlight: add subdrivers & Tegra support

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Date:	Tue, 22 Jan 2013 08:17:26 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Mark Zhang <markz@...dia.com>,
	"gnurou@...il.com" <gnurou@...il.com>
Subject: Re: [PATCH 0/3] pwm-backlight: add subdrivers & Tegra support

On Mon, Jan 21, 2013 at 05:18:11PM +0900, Alex Courbot wrote:
> Hi Thierry,
> 
> On Monday 21 January 2013 15:49:28 Thierry Reding wrote:
> > Eventually this should all be covered by the CDF, but since that's not
> > ready yet we want something ad-hoc to get the hardware supported. As
> > such I would like to see this go into some sort of minimalistic, Tegra-
> > specific display/panel framework. I'd prefer to keep the pwm-backlight
> > driver as simple and generic as possible, that is, a driver for a PWM-
> > controlled backlight.
> > 
> > Another advantage of moving this into a sort of display framework is
> > that it may help in defining the requirements for a CDF and that moving
> > the code to the CDF should be easier once it is done.
> > 
> > Last but not least, abstracting away the panel allows other things such
> > as physical dimensions and display modes to be properly encapsulated. I
> > think that power-on/off timing requirements for panels also belong to
> > this set since they are usually specific to a given panel.
> > 
> > Maybe adding these drivers to tegra-drm for now would be a good option.
> > That way the corresponding glue can be added without a need for inter-
> > tree dependencies.
> 
> IIRC (because that was a while ago already) having a Tegra-only display 
> framework is exactly what we wanted to avoid in the first place. This series 
> does nothing but leverage the callbacks mechanism that already exists in pwm-
> backlight and make it available to DT systems. If we start making a Tegra-
> specific solution, then other architectures will have to reinvent the wheel 
> again. I really don't think we want to go that way.
> 
> These patches only makes slight changes to pwm_bl.c and do not extend its 
> capabilities. I agree that a suitable solution will require the CDF, but by 
> the meantime, let's go for the practical route instead of repeating the same 
> mistakes (i.e. architecture-specific frameworks) again.
> 
> There are certainly better ways to do this, but I'm not convinced at all that 
> a Tegra-only solution is one of them.

Well, your proposal is a Tegra-only solution as well. Anything we come
up with now will be Tegra-only because it will eventually be integrated
with the CDF.

Trying to come up with something generic would be counter-productive.
CDF *is* the generic solution. All we would be doing is add a competing
framework.

Thierry

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