[PATCH] [TWL4030 MADC] Fix ADC[3:6] readings

[Adam Lee]

Hello, here is some more context from the TPS65950's TRM [1].

Quoting from section 15.3.1.2.1 VUSB3V1 section:

    "VUSB3V1 is also used to bias analog multiplexers on the four MCPC
pins between the carkit and the MADC (supplied by VINTANA2)."


And from section 15.4.11. MADC Monitoring Using MCPC:

    "Four MCPC pins can be selected as analog conversion input pins by
setting the CARKIT_ANA_CTRL[3] SEL_MADC_MCPC bit."

My patch addresses both (set the register, and enable 3v1). And yes it
has been tested on Gumstix Overo COMs (OMAP3 + TPS65950).

Hope to hear from IIO maintainers!

[1] http://www.droid-developers.org/images/2/21/Tps65950_TRM.pdf

On Fri, Jul 17, 2015 at 2:42 AM, Peter Meerwald <pmeerw at pmeerw.net> wrote:
> Hello,
>
> adding linux-iio...
>
>> To get a chance of this patch being considered for inclusion, you
>> should send this to the maintainers of the phy and iio framework.
>> There is a high chance, that none of them will see your mail.
>>
>> On Thu, Jul 16, 2015 at 03:20:27PM -0700, Adam YH Lee wrote:
>> > MADC[3:6] reads incorrect values without these two following changes:
>>
>> uhm MADC[3:6] are externally available analog inputs. Your
>> change will result in them being tied to the USB module.
>
> change regarding TWL4030_USB_SEL_MADC_MCPC is necessary at
> least for some hardware revisions to get proper ADC values
>
>> > - enable the 3v1 bias regulator for ADC[3:6]
>>
>> The regulator is not required for correct MADC functionality, but
>> for correct USB measureing. The regulator should not be requested
>> by the madc module, but by the usb module, which is connected to
>> the madc.
>
> in my experience, the MADC exhibits several strange things, I wouldn't be
> surprised that this bias is somehow necessary for operation even if it is
> not what the spec says -- has this been tested?
>
>> > - configure ADC[3:6] lines as input, not as USB
>>
>> I don't think that should be done for all boards.
>>
>> > [...]
>>
>> -- Sebastian
>>
>
> --
>
> Peter Meerwald
> +43-664-2444418 (mobile)