[RFC/PATCH] lost arbitration detection for PCF8584

[Eric Brower]

Attached is a patch for detecting lost arbitration via the PCF8584 
algorithm adapter.  The documentation from Philips is not clear on the 
topic, and it seems I could be checking the LAB bit more frequently, but 
this seems to do the trick on a system for which I am developing I2C 
support-- any comments on these modifications for multi-master friendliness?

The result of this patch is that callers of the master_xfer function 
pointer will receive -EINTR when work has been interrupted by a detected 
lost arbitration.  Checking the lost arbitration (LAB) bit is done only 
in wait_for_pin().  This -EINTR bubbles-up all the way to the callers of 
the i2c library functions for accessing the bus and smarter callers 
should be able to retry as appropriate for their task-- this does, 
however, prevent the master_xfer routine from returning the number of 
messages successfully sent; I'm not sure where the best tradeoff could 
be made, given the API (and the fact that I seem to be the only person 
who would find this useful) but I suppose lost arbitration could just 
become another anonymous failure mode and we continue to report back the 
number of successful messages sent.

Any comments?

Many thanks,
E
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