RTC woes

RTC woes

[Marc LeFevre]

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Hi:

I'm new to the list.  I have an e500-based embedded Linux system running a
2.6.22 kernel.  I have a PCF8563T i2c based RTC chip attached to the PPC i2c
bus.  In my kernel config file I have selected CONFIG_RTC_INTF_DEV=y and
CONFIG_RTC_DRV_PCF8563=y.  I do a mknod  for /dev/rtc as c 10 135 (standard
Linux) and link /dev/rtc0 to it.

 

When I boot, get the following message:

 

drivers/rtc/hctosys.c: unable to open rtc device (rtc0)

 

and, of course I cannot access /dev/rtc after booting.  I can, however, talk
to the rtc if I use /dev/i2c and a generic i2c read and write utility.

 

When I look in /proc/devices, I see that rtc has taken major number 254
which puzzles me. RTC should not need a dynamic major number, right?  I have
perused the drivers in linux/drivers/rtc and don't find any of them calling
register_chrdev() to get a dynamic major number.  So here are my questions:

 

1)       Shouldn't rtc automagically use major/minor 10/135?

2)       How can I find where in the source it asks for a dynamic major
number?

3)       Does the PPC have some quirks regarding i2c operation that are at
the root of this problem?

 

BYW, I tried making the rtc device file as c 254 0 to match what's in
/proc/devices and that gives me the same bejavior.

 

Thanks in advance for any help you can offer.

 

Marc

 


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Re: RTC woes

[Clemens Koller]

Marc LeFevre schrieb:
> I’m new to the list.

Welcome! :-)

 > I have an e500-based embedded Linux system running
> a 2.6.22 kernel.  I have a PCF8563T i2c based RTC chip attached to the 
> PPC i2c bus.  In my kernel config file I have selected 
> CONFIG_RTC_INTF_DEV=y and CONFIG_RTC_DRV_PCF8563=y.  I do a mknod  for 
> /dev/rtc as c 10 135 (standard Linux) and link /dev/rtc0 to it.
> 
  > When I boot, get the following message:
> 
> drivers/rtc/hctosys.c: unable to open rtc device (rtc0)

2.6.22.x and 2.6.23.x i2c rtc code was quite messy around PCF8563.

> 3)       Does the PPC have some quirks regarding i2c operation that are 
> at the root of this problem?

The RTC subsystem was improved quite a bit lately. Try 2.6.24' powerpc
architecture with a proper device tree instead. It works over here on
mpc8540 / mpc8548 whereas the older ones were just a waste of time.

Regards,

Clemens