Hello all, I am currently working on a hwmon/pmbus driver for a PMBus capable 3Y Power/FSP power supply (YH5301-1EAR).
The datasheet has limited information. But with the help of some online sources, other datasheets from the vendor and the pmbus sub-system I could figure out most of it. However, I did run in some troubles with the VOUT values. To my understanding (and from what I could validate) the device does encode _all_ values as "LINEAR11". Meaning all values have a mantissa of 11 bit and the exponent in the other 5 bits of the register word. This causes some troubles with the read out of the VOUT registers (e.g. READ_VOUT). The pmbus subsystem expects these values to be in "LINEAR16" encoding. Hence the full word register is the mantissa and the exponent is supposed to be in VOUT_MODE. Sadly, the VOUT_MODE register isn't supported. It reads 0xFF. In my first attempt to work around this, I provided a custom read_word_data function that would fixup the value. However, that did lead to problems with negative values and also had a precision loss (12,09V -> 12V). I tried to compensate by faking the values as 'direct' and adjusting the m/b/R values to match. This is also not perfect, as it is messy and also seems to report the wrong values in some cases. I think the best solution would be to prevent pmbus (more specifically 'pmbus_reg2data_linear') to treat the obtained value as LINEAR16. A quick hack shows me that this would work with all the reported values of the device. However, this means proving da vendor/device specific workaround by changing a generic component. I am not sure how you feel about this. Ultimately, I'd like to upstream the driver (and potential fix), so I would like to find a solution that is fine with you all. My current proposal would be to introduce a flag in pmbus_platform_data.flags that allows to disable the LINEAR16 switch in case the sensor has the class PSC_VOLTAGE_OUT. At least this seems the change with the smallest impact. I am not sure how to name the flag but to propose something I'd say 'PMBUS_VOUT_IS_LINEAR11' What do you think? Kind regards Christian -- Christian GRÖNKE INFODAS GmbH ~ Rhonestraße 2 ~ 50765 Köln ~ Germany Phone: +49 221 70912 187 ~ Mail: [email protected]
