[lm-sensors] Problem with detection or PMBus devices

Guenter Roeck guenter.roeck at ericsson.com
Tue Oct 12 17:47:18 CEST 2010

On Tue, Oct 12, 2010 at 05:06:09AM -0400, Jean Delvare wrote:
> Hi Guenter,
> On Mon, 11 Oct 2010 16:47:57 -0700, Guenter Roeck wrote:
> > I have been trying to add device detection for PMBus devices to sensors-detect.
> > It works fine for LTC2978.
> > 
> > Problem is that BMR45x chips do not support QUICK commands. As a result, detection
> > code fails early on.
> > 
> > Would it make sense to extend the detection code to also try other commands
> > (eg BYTE_DATA) if QUICK does not work, or would that be too risky ?
> The SMBus quick write command isn't better or worse than a few other
> SMBus commands as far as device detection is concerned. We are using it
> extensively for historical reasons: read commands used to lock up the
> SMBus on some systems when ran on clock devices. But we no longer probe
> the problematic addresses (0x69 and 0x69 mainly) anyway.
> We already have a number of workarounds in place for specific cases
> (see sub i2c_probe). Depending on the address at which your BMR45x chip
> lives, a similar trick might be suitable.
Valid address range is [0x03..0x0a, 0x0d..0x3f]. So it is quite a broad range.

> We may progressively move to using SMBus byte reads as the default
> probing method. After all, the actual device identification routines
> all use this command type. If this would cause any trouble, we would
> know by now. As long as i2c_safety_check() is called first, I can't
> think of any problem resulting from this change, and this would avoid
> the problem of adapters not supporting quick commands.
Ok, I'll try that. Note the problem here is not the adapter - apparently
it is the bmr chips which don't support quick commands. Other chips on the
same adapter (such as the ltc2978 and max6696) are detected fine with
quick commands.


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