linux-kernel - Re: [PATCH v6 1/4] Runtime Interpreted Power Sequences

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Date:	Thu, 13 Sep 2012 10:32:38 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
Cc:	Sascha Hauer <s.hauer@...gutronix.de>,
	Alex Courbot <acourbot@...dia.com>,
	Stephen Warren <swarren@...dia.com>,
	Simon Glass <sjg@...omium.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Anton Vorontsov <cbou@...l.ru>,
	David Woodhouse <dwmw2@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	Leela Krishna Amudala <l.krishna@...sung.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v6 1/4] Runtime Interpreted Power Sequences

On Thu, Sep 13, 2012 at 11:00:18AM +0300, Tomi Valkeinen wrote:
> Yes, I think the backlight and the panel should be considered separate
> devices. Just like, say, a touch screen and a panel may happen to be in
> the same display module, a backlight and a panel can be in the same
> display module. They are still separate, independent things, although
> they are, of course, used together.

Still, as Alex mentioned, there may be some dependency between the panel
and the backlight, so we may need to have some kind of connection. I
haven't had much time to look at the panel subsystem, but perhaps it
should provide for this.

I obviously don't know every panel and backlight combination out there,
but isn't the dependency more of a usability nature. What I mean is that
the panel will work even if you switch the backlight on immediately,
just that the panel might take some time to properly display data and
therefore the backlight should remain powered off so the user doesn't
see garbage. Or are there really any functional dependencies?

Thierry

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