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Accessing ls1021a-twr SNVS RTC in linux

Question asked by Jason Hendrix on Feb 19, 2016
Latest reply on Feb 22, 2016 by Jason Hendrix

Hi,  our custom board will use the on-board battery backed RTC on the LS1020a processor.  In the meantime, I'm trying to use that (on-chip) RTC on the LS1021ATWR dev board.  Eventually I would like to configure it as RTC0 and link it to hwclock.  I can't seem to get my system to link the driver and the device (if the device is even recognized).

Can anyone help me configure Linux to use the on-chip LP RTC as RTC0?

 

Here is what I've done:

  • I enabled the snvs_rtc in the config file (using menuconfig)
  • I added data to the device tree files ls1021a.dtsi and ls1021atwr.dts
  • Build, load, run

 

To ls1021a.dtsi I added the following node under "soc":

sec_mon: sec_mon@1e90000 {

     compatible = "fsl,sec-v4.0-mon";

     #address-cells = <1>;

     #size_cells = <1>;

     ranges = <0 0x01e90000 0x10000>;

     interrupts = <GIC_SPI 110 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 111 IRQ_TYPE_LEVEL_HIGH>;

 

     snvs_rtc: snvc_rtc_lp@34 {

          compatible = "fsl, sec-v4.0-mon-rtc-lp";

          reg = <0x34 0x58>;

     };

};

 

To ls1021atwr.dts I added the following node at the end of the file:

&svns_rtc {

     status = "okay";

};

 

--------------------------------------------------------------------------------

Now, when I load and run, I see:

  • /proc/device-tree/soc/sec_mon@1e90000/snvs_rtc_lp@34
  • /sys/bus/platform/drivers/snvs_rtc (containing only bind, unbind, uevent)
  • /sys/bus/platfrom/devices/sec_mon.3
  • /sys/devices/soc.2/sec_mon.3

But, the driver doesn't seem to be bound to the device.  I actually tried:

echo -n "sec_mon.3" > /sys/bus/platform/drivers/snvs_rtc/bind

but the OS returned "No such device"

 

Some things I think might be wrong:

  • device tree configuration not correct - should I put it under soc, as I did?
  • In some support posts for this RTC on the imx6 platform, there is some discussion of having to blow a fuse.  Is that required on this chip?

 

Thanks in advance.

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