linux-kernel - Re: [PATCH 5/5] rtc: at91sam9: add DT bindings documentation

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Date:	Wed, 10 Sep 2014 14:43:15 +0200
From:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Andrew Victor <linux@...im.org.za>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	rtc-linux@...glegroups.com, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] rtc: at91sam9: add DT bindings documentation

Hi Johan,

On Wed, 10 Sep 2014 14:14:24 +0200
Johan Hovold <johan@...nel.org> wrote:

> On Wed, Sep 03, 2014 at 10:45:34AM +0200, Boris BREZILLON wrote:
> > Signed-off-by: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> > ---
> >  .../devicetree/bindings/rtc/atmel,at91sam9-rtc.txt   | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.txt b/Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.txt
> > new file mode 100644
> > index 0000000..9ca455f
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.txt
> > @@ -0,0 +1,20 @@
> > +Atmel AT91SAM9260 Real Time Timer
> > +
> > +Required properties:
> > +- compatible: should be: "atmel,at91sam9260-rtt"
> > +- reg: should contain 2 memory regions
> > +  * the first one encodes the memory region of the RTT controller
> > +  * the second one encodes the GPBR (General Purpose Backup Resgisters)
> > +    memory region used to store the current time
> > +- interrupts: rtc alarm/event interrupt
> > +- clocks: should contain one clock pointing the the slow clk
> > +
> > +Example:
> > +
> > +rtc@...ffe00 {
> > +	compatible = "atmel,at91sam9260-rtt";
> > +	reg = <0xfffffd20 0x10
> > +	       0xfffffd50 0x4>;
> > +	interrupts = <1 4 7>;
> > +	clocks = <&clk32k>;
> > +};
> 
> This does not describe the hardware, but rather a specific software
> configuration.
> 
> The RTT is first of all not an RTC (although it can be used as one in a
> specific software configuration). And the second register resource above
> is not an RTT register, but a general-purpose backup register could be
> used for other purposes (which register to use is currently configurable
> for legacy booting using CONFIG_RTC_DRV_AT91SAM9_GPBR).
> 
> This was discussed in the thread where I posted an RFC for this last
> year (which you linked to in your original submission thread), but no
> conclusion was reached:
> 
> 	http://www.spinics.net/lists/arm-kernel/msg236292.html

Yes, I read this thread.

Please, lets just find a solution, even if it's not a perfect one,
because the situation is unacceptable.
We're missing this features since the move to DT because we were not
able to agree on a DT binding...

I know DT bindings are supposed to represent HW parts and not what
they're used for or how they're configured, but do you see any other
real usage of the RTT block ?

BTW, I don't care which binding/implementation is chosen but we need to
sort this out!

Best Regards,

Boris


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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