[Voyage-linux] RE: [lm-sensors] scx200_acb: unexpected ACBCTL2 readback

BGardner at Wabtec.com BGardner at Wabtec.com
Tue Jan 3 23:49:52 HKT 2006

Hi Mike, Joe -

It looks like the scx200_acb driver scans two IO addresses by default
(0x820, 0x840).
One of them doesn't exist. That explains the ACBCTL2 readback problem.
You should be able to get rid of that message by using the 'base' module
Here's a guess at the format.
$ modprobe scx200_acb base=0x820,0

In [1], Joe mentioned a 15 second delay.

The scx200_acb driver has a flaw where it misses the NACK indication
when it tries to write to an address that doesn't exist. This causes it
to timeout instead of immediately returning a failure.  Likely, your
hardware is 'scanning' for around 15 devices that don't exist. 

Refer to this patch for a possible fix: 

Another thing to do is to add 'ignore' parameters to modprobe so that
the chip drivers don't scan for devices that don't exist.

For example, I use this for my lm83:
$ modprobe lm83 force=0,0x4c


> -----Original Message-----
> From: lm-sensors-bounces at lm-sensors.org 
> [mailto:lm-sensors-bounces at lm-sensors.org] On Behalf Of 
> Michael Renzmann
> Sent: Tuesday, January 03, 2006 1:53 AM
> To: lm-sensors
> Subject: [lm-sensors] scx200_acb: unexpected ACBCTL2 readback
> Hi.
> On the voyage-linux mailing list there recently has been a 
> report about
> a problem related to scx200_acb in 2.6.x kernels. The 
> original report is
> at [1], a short but more detailed analysis of the problem is at [2]. 
> The problem seems to be that loading scx200_acb fails during 
> the probing
> phase, but loading and using LM77 after that still works fine. Quoting
> [2]:
> === cut ===
> Same here with a non-voyage 2.6.11 kernel. I enabled 
> debugging and added
> a bit more info into the relevant message and I get:
> i2c /dev entries driver
> scx200_acb: ACBCTL2 readback failed, got 0xff
>   : probe failed
> The driver write 0x70 to ACBCTL2 and expects to read 0x70 back, but it
> gets 0xff instead. Looked into the manual briefly, but seems too
> complicated to figure out quickly. As you mention, lm77 works fine
> thereafter. Weird...
> === cut ===
> Comments?
> Bye, Mike
> [1]
> http://list.voyage.hk/pipermail/voyage-linux/2005-December/000548.html
> [2]
> http://list.voyage.hk/pipermail/voyage-linux/2006-January/000565.html
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