Re: [PATCH hwmon-next v3 2/3] hwmon: (pmbus) Add support for MPS Multi-phase mp2888 controller

[Guenter Roeck <linux@roeck-us.net>]

On 5/3/21 9:11 AM, Vadim Pasternak wrote:
> Hi Guenter!
> 
...
>>> +	case PMBUS_VIN_OV_FAULT_LIMIT:
>>> +	case PMBUS_VIN_UV_WARN_LIMIT:
>>> +		ret = pmbus_read_word_data(client, page, phase, reg);
>>> +		if (ret <= 0)
>>> +			return ret;
>>> +
>>> +		val = mp2888_reg2data_linear11(ret, PSC_VOLTAGE_IN);
>>> +		ret = val * MP2888_VIN_MANTISSA;
>>> +		break;
>>
>> Unless I am missing something, this is linear11 with, for some reason, bit 10
>> erroneously set for PMBUS_READ_VIN. That means that setting the format
>> for PSC_VOLTAGE_IN and clearing bit 10 for PMBUS_READ_VIN should work
>> without local conversion. Am I missing something ?
> 
> On board I have vin 12V.
> From register I am getting 0xed80.
> If I am masking bit 10, 0xe980, it gives me 48.12 V, masking bits 11,10 gives 24.00.
> For getting 12, I should mask bits 11, 10 and shift left bits 8 - 0.
> But I it doesn't look right things to do. 
> 
Turns out that is because the data format for READ_VIN is not linear11,
it is something like linear10. The mantissa is 10 bit (unsigned), the
exponent is 6 bit. So the exponent is -5, not -6 as one would assume.

With that in mind, I'd still prefer to fix up READ_VIN to linear11
instead of converting the limits to direct mode.

Thanks,
Guenter