Hi Guenter, On Thu, Jan 30, 2014 at 08:01:02PM -0800, Guenter Roeck wrote: > Hi Sören, > > On Thu, Jan 30, 2014 at 05:13:42PM -0800, Sören Brinkmann wrote: > > Hi Guenther, > > > > I recently became aware of some weird behavior when using the UCD9000 > > driver for voltage monitoring. We use that device on our zc706 Zynq > > platform to generate 5 voltage rails. Observing the voltages in Linux > > showed a correct value for rail 1 but a 2x error in in rails 2-3 and a > > 4x error in rail 5. Digging through specs, docs and sources I could > > track this down to this: > > - The PMBus core assumes one VOUT_MODE register per chip > > - UCD90120 has VOUT_MODE registers per rail > > > > In our setup we have an exponent of -14 for rail 1, -13 for rails 2-4 and > > -14 for rail 5. The PMBus core only reads and uses the first one and > > applies it to all rails. > > > > I'm not sure whether the UCD devices don't comply to spec or whether > > this is a bug in the PMBus core, either way, the reported values from > > the driver are prone to be wrong/scaled by an unknown factor. > > > The PMBus specification is sufficiently vague to ensure that pretty much > any interpretation of it is PMBus compliant. > > > Is this somehow known behavior for which a workaround might be > > available? Otherwise, if you know how an acceptable solution might look > > like, I might find some time and give it a shot. > > > I think we may have to expand the driver to detect and configure the exponent > per rail/page. At least I can not think of another solution right now. > > Can you test the patch below ? Completely untested, but it compiles. > It will likely need some refinement (for example, other chips may not even > have the VOUT_MODE command on non-zero pages), but should be useful for > testing. That was fast, thanks. The patch works. With it, the driver reports the correct voltages. I suspect that the UCD9200 were affected as well. Unfortunately, in our configs for those the exponents across all rails are the same, so I don't see things go wrong. You can add my Tested-by: Sören Brinkmann <soren.brinkmann@xxxxxxxxxx> Let me know if you need a different patch to be tested. Thanks, Sören _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
