linux-kernel - Re: [PATCH v4 1/3] Runtime Interpreted Power Sequences

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Date:	Tue, 21 Aug 2012 11:57:45 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
Cc:	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 <leelakrishna.a@...il.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-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] Runtime Interpreted Power Sequences

On Tue, 2012-08-21 at 10:33 +0200, Thierry Reding wrote:

> I suppose power sequences aren't needed if you have a specific driver
> for every panel out there. However that also means that you'd have to
> write drivers for literally every panel that requires support. In the
> end this will just result in discussion down the road how the common
> functionality can be refactored and we may end up with power sequences
> again.
> 
> Also as you mentioned, power sequences are useful for a number of other
> use-cases. Without power sequences you'll have to potentially create
> extra frameworks tha reimplement parts of the power sequence code for
> their specific hardware needs.

Right. I think my main concern is the use of DT data, not power
sequences as such. I've been going back and forth in my mind with this
issue with OMAP also.

The question is: what stuff belongs to DT data and what belongs to the
kernel? I've been trying to go to the direction where DT is used to
describe the HW connections of different IP blocks and to pass board
specific configuration. Everything else is in the driver.

This doesn't mean that we'd have a separate driver for each device. For
example, we have a generic panel driver in OMAP, which contains a kind
of small panel database. The panel database contains the name of the
panel as a key, and panel specific configuration as a value. This
configuration could also contain some kind of generic power sequence.

I'd like to require the board developer to only fill in to the DT data
what panel he is using, and how it's connected on his board. Not panel's
internal functionality.

The one benefit I see with DT based approach is that if we have, say,
10000 panels, we'd have quite a big database in kernel memory and a
board may only need one or two of those. But perhaps that could be
helped with the use of __initdata.

 Tomi

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