Device tree and external RTC

Guennadi Liakhovetski g.liakhovetski at
Fri Oct 5 05:52:19 EST 2007

On Thu, 4 Oct 2007 Bruce_Leonard at wrote:

> Guennadi Liakhovetski <g.liakhovetski at> wrote on 10/04/2007 02:29:06 
> AM:
> > 
> > It shall not hurt, but do you really have this one?
> I turned this on because my clock is a SMT M41T00.  Not sure why it's 
> called a sensor in the .config.

It is the deprecated driver for the same rtc chip. But maybe it is this 
one that makes your RTC work ATM, see below.

> > First, this might be either a userspace or a kernel problem. Do you have 
> > the correct device nodes? Are you using udev? Should be something like 
> Ultimatly it was my own stupididty that did me in.  You are absolutly 
> correct, I didn't have the right device nodes and because we're limited on 
> space we don't want to use udev.  Once I created the rtc0 device and 
> linked rtc to it, hwclock started working correctly.

It shouldn't. It probably does thanks to the m41t00 driver, but you don't 
want it, instead...

> > you need suitable entries in arch/powerpc/sysdev/fsl_soc.c in the 
> > i2c_devices array. I think, patch at 
> > is exactly what you 
> > need. 
> I'll give this a try.  I'd really prefer to be using the device tree for 
> this, but I guess as long as I have it working using configuration options 
> in the kernel it doesn't really matter.  Either way I don't have to write 
> any special board support code for the kernel.

you need this patch to get ds1307 attach to your rtc chip.

And, besides, linuxppc-embedded is deprecated, linuxppc-dev should be used 

Guennadi Liakhovetski

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