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

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Message-ID: <20120913071829.GE6180@pengutronix.de>
Date:	Thu, 13 Sep 2012 09:18:29 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
Cc:	Alex Courbot <acourbot@...dia.com>,
	Stephen Warren <swarren@...dia.com>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	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 10:03:27AM +0300, Tomi Valkeinen wrote:
> On Thu, 2012-09-13 at 09:00 +0200, Sascha Hauer wrote:
> > On Thu, Sep 13, 2012 at 09:54:09AM +0300, Tomi Valkeinen wrote:
> > > On Thu, 2012-09-13 at 15:36 +0900, Alex Courbot wrote:
> > > > On Thursday 13 September 2012 14:22:57 Tomi Valkeinen wrote:
> > > >  
> > > > > However, I fear these board specific things may be quite a bit anything,
> > > > > so it may well be pwm, gpios and regulators are not enough for them. For
> > > > > example, there could be an FPGA on the board which requires some
> > > > > configuration to accomplish the task at hand. It could be rather
> > > > > difficult to handle it with a generic power sequence.
> > > > 
> > > > Right. Note that this framework is supposed to be extended - I would like to 
> > > > at least add regulator voltage setting, and maybe even support for clocks and 
> > > > pinmux (but that might be out of place).
> > > 
> > > Yes, that's one concern of mine... I already can imagine someone
> > > suggesting adding conditionals to the power sequence data. Perhaps also
> > > direct memory read/writes so you can twiddle registers directly.

These memory writes can be avoided when these registers are abstracted
as a regular gpio/regulator/pwm driver.

> > > And so
> > > on. Where's the limit what it should contain? Can we soon write full
> > > drivers with the DT data? =)
> > 
> > I have this concern aswell, that's why I'm sceptical about this patch
> > set. But what are the alternatives? Adding power code to the drivers and
> > thus adding board specific code to them is backwards.
> 
> As was pointed out in earlier posts in this thread, these are almost
> always device specific, not board specific.
> 
> Do you have examples of board specific power sequences or such?

Sure, tons of. One board needs a gpio to be set high to enable backlight,
the next one to low, a regulator has to be enabled, and to avoid
flickering a certain timing has to be ensured. This is all highly board
specific.

Sascha

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