linux-kernel - Re: [PATCH 2/8] iio: adc: axp20x_adc: add support for AXP813 ADC

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Date:   Mon, 11 Dec 2017 09:18:55 +0100
From:   Quentin Schulz <quentin.schulz@...e-electrons.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     sre@...nel.org, robh+dt@...nel.org, mark.rutland@....com,
        wens@...e.org, linux@...linux.org.uk,
        maxime.ripard@...e-electrons.com, lee.jones@...aro.org,
        knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-iio@...r.kernel.org, icenowy@...c.io,
        linux-sunxi@...glegroups.com, thomas.petazzoni@...e-electrons.com
Subject: Re: [PATCH 2/8] iio: adc: axp20x_adc: add support for AXP813 ADC

Hi Jonathan,

On 10/12/2017 17:36, Jonathan Cameron wrote:
> On Mon,  4 Dec 2017 15:12:48 +0100
> Quentin Schulz <quentin.schulz@...e-electrons.com> wrote:
> 
>> The X-Powers AXP813 PMIC is really close to what is already done for
>> AXP20X/AXP22X.
>>
>> There are two pairs of bits to set the rate (one for Voltage and Current
>> measurements and one for TS/GPIO0 voltage measurements) instead of one.
> 
> This would normally imply we need to split the device into two logical
> IIO devices.  However, that only becomes relevant if we are using
> buffered output which this driver doesn't support.
> > It'll be nasty to deal with this if we add that support down the line
> though.  Up to you though as it's more likely to be your problem than
> anyone else's :)
> 

I have no plans for supporting buffered output for the AXPs at the
moment. But that's an interesting (and important) limitation to raise.
Wouldn't be more of a hack to have two IIO devices representing the
actual same IP?

> For now you could elect to support the different sampling frequencies
> if you wanted to but just providing controls for each channel.
> 

I guess that you're offering to use IIO_CHAN_INFO_SAMP_FREQ in
info_mask_separate for each channel?

> Given the driver doesn't currently expose these at all (I think)
> this is all rather immaterial ;)

I'm not giving the user the option to chose the sampling frequency for
now. I have no plans to do it either, but I think it would be rather
simple to later add support for setting frequency sampling since we only
need to add a sysfs entry (with IIO_CHAN_INFO_SAMP_FREQ) that does not
exist yet. Don't you think? Am I missing something?

Thanks,
Quentin
-- 
Quentin Schulz, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com