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

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Message-ID: <6871054.sK10m5bePf@percival>
Date:	Mon, 21 Jan 2013 17:18:11 +0900
From:	Alex Courbot <acourbot@...dia.com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
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

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.

Alex.

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