linux-kernel - Re: [PATCH] video: ARM CLCD: Added dt support to set tim2 register

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Date:	Tue, 03 Mar 2015 10:22:07 +0000
From:	Pawel Moll <pawel.moll@....com>
To:	Arun Ramamurthy <arun.ramamurthy@...adcom.com>
Cc:	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazau <anatol@...gle.com>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	Ray Jui <rjui@...adcom.com>,
	"bcm-kernel-feedback-list@...adcom.com" 
	<bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH] video: ARM CLCD: Added dt support to set tim2 register

On Tue, 2015-03-03 at 10:02 +0000, Pawel Moll wrote:
> On Mon, 2015-03-02 at 19:09 +0000, Arun Ramamurthy wrote:
> > > The existing bindings intentionally avoided quoting internal registers -
> > > they are supposed to describe how the hardware is wired up...
> > >
> > > So how about something like "arm,pl11x,tft-invert-clac"? Then the driver
> > > sets the bit or not, depending on the property existance?
> > >
> > Sure, I can change it to two properties called arm,pl11x,tft-invert-clac 
> > and arm,pl11x,tft-clksel. Would that be acceptable?
> 
> That would be fine by me :-)

Or (after having a look at the TRM) I should rather say: the invert-clac
is fine by me :-) but the tft-clksel doesn't work, I afraid.

If I'm not mistaken, there are two problems with it.

Number one: it's not TFT-specific, is it? So it certainly should not
have the "tft-" bit.

Number two: setting this bit says "do not use CLCDCLK for the logic; use
HCLK instead", correct? If so, have a look at the clock properties. They
say:

- clock-names: should contain "clcdclk" and "apb_pclk"

- clocks: contains phandle and clock specifier pairs for the entries
        in the clock-names property. See

So if your hardware has the reference clock wired to HCLK, and you
defining the clocks as "clcdclk", you are (no offence meant ;-)
lying :-)

So how about solving the problem by extending the clock-names definition
like this (feel free to use own wording):

- clock-names: should contain two clocks, either "clcdclk" or "hclk"
               (depending on which input is to be used as a reference
               clock by the controller logic) and "apb_pclk"

That way you're precisely describing the way the hardware is wired up.
And the driver simply tries to get clcdclk first, if it's defined -
cool, set clksel to 1, if not - try hclk and set clksel to 0. If neither
of them is present - bail out.

Does this make any sense?

Pawel

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