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Date: Wed, 10 Sep 2014 17:07:02 +0200
From: Johan Hovold <johan@kernel.org>
To: Boris BREZILLON <boris.brezillon@free-electrons.com>
Cc: Johan Hovold <johan@kernel.org>, Nicolas Ferre <nicolas.ferre@atmel.com>,
        Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
        Alexandre Belloni <alexandre.belloni@free-electrons.com>,
        Andrew Victor <linux@maxim.org.za>,
        Alessandro Zummo <a.zummo@towertech.it>, rtc-linux@googlegroups.com,
        Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] rtc: at91sam9: add DT bindings documentation
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On Wed, Sep 10, 2014 at 03:20:19PM +0200, Boris BREZILLON wrote:
> On Wed, 10 Sep 2014 14:14:24 +0200
> Johan Hovold <johan@kernel.org> wrote:

> > 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).
> 
> We could use a syscon device (which exposes a regmap) for the GPBR
> block.
> 
> rtc@ffffff20 {

rtt

> 	compatible = "atmel,at91sam9260-rtt";
> 	reg = <0xfffffd20 0x10>;
> 	interrupts = <1 4 7>;
> 	clocks = <&clk32k>;
> 	atmel,time-reg = <&gpbr 0x0>;
> };
> 
> gpbr: syscon@fffffd50 {
> 	compatible = "atmel,at91sam9260-gpbr", "syscon";
> 	reg = <0xfffffd50 0x10>;
> 	
> };

Yes, this essentially what I suggested in the thread (and my last reply)
and relying on syscon rather than a custom driver seems like a good
idea. It would allow early access to the registers too with the recently
proposed changes. It would not guarantee any kind of exclusivity,
though, but I guess that's tolerable?

Johan