Re: [PATCH] hwmon: (pmbus/lm25066) Swap low/high current coefficients for LM5066(i)

[Guenter Roeck]

Hi Rob,

On 11/22/2017 03:39 PM, Rob Lippert wrote:
> On Wed, Nov 22, 2017 at 3:28 PM, Guenter Roeck <linux@xxxxxxxxxxxx> 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.

Guenter