On Wed, 10 Sep 2014 17:07:02 +0200
Johan Hovold [off-list ref] wrote:

On Wed, Sep 10, 2014 at 03:20:19PM +0200, Boris BREZILLON wrote:

quoted

On Wed, 10 Sep 2014 14:14:24 +0200
Johan Hovold [off-list ref] wrote:

quoted

quoted

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 at ffffff20 {

rtt

quoted

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

gpbr: syscon at 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?

Yep, that's one of the concern I had with the syscon/regmap
approach :-(, but I guess I'll give this solution a try and post a new
version of this series ;-).

Can we just leave the rtt as an rtc problem on the side for now and bind
it to the rtc-at91sam9 driver.

If we ever decide to add a new driver using the RTT for another purpose
we will still be able to reference the RTT block like this (and keep
the existing rtt node definition):


rtt-based-rtc {
	compatible = "atmel,rtt-rtc";
	atmel,rtt = <&rtt>;
	atmel,time-reg = <&gpbr 0x0>;
}

rtt-based-xdev {
	compatible = "atmel,rtt-xdev";
	atmel,rtt = <&rtt>;
	/*...*/
}

Regards,

Boris

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