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Date:   Wed, 22 Nov 2017 17:17:44 -0800
From:   Guenter Roeck <>
To:     Rob Lippert <>
Cc:     Robert Lippert <>,,,,
        Xo Wang <>
Subject: Re: [PATCH] hwmon: (pmbus/lm25066) Swap low/high current coefficients
 for LM5066(i)

Hi Rob,

On 11/22/2017 03:39 PM, Rob Lippert wrote:
> On Wed, Nov 22, 2017 at 3:28 PM, Guenter Roeck <> wrote:
>> On Wed, Nov 22, 2017 at 02:07:28PM -0800, Robert Lippert wrote:
>>> The _L low-current mode coefficient values should reference the
>>> datasheet rows with CL=VDD but it seems were mistakenly pulled from
>>> the rows with CL=GND.
>>> This causes the current/power to be reported as approximately double
>>> the actual value when CL=GND and half the actual value when CL=VDD.
>> This would affect all chips supported by this driver. Hmm, and I was sure
>> I tested this. I'll have to dig out my hardware and confirm.
> I'm still not 100% convinced this commit is correct as I haven't been
> able to validate the measurements against an external probe yet (and
> my test board uses a non-standard sense resistor which means it needs
> additional massaging of the data anyhow).
>> The code currently only uses bit 4 of the DEVICE_SETUP (D9h) command
>> to determine which current limit setting to use. Looking into the
>> datasheet, it looks like it also has to evaluate bit 2, and I wonder
>> if there is a means to determine CL if bit 2 = 0. Any idea ?
> On my test board CL=floating (equivalent to GND) and the value of
> register 0xD9 is all zeroes.
Are you sure that floating is equivalent to GND ? I didn't check the
datasheet, but it is more common for chips to have an internal pull-up.

>> Does bit 4 report the CL pin value if bit 2 = 0 ?
> I can't tell by reading the datasheet that 0xD9 bit4 will ever report
> the pin value as the language is difficult to parse :)

Same here.

> But I don't have any hardware setup with CL=VDD to test...

I do have various evaluation boards, so I should be able to do some testing.
I hope I'll get to it over the weekend.


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