linux-kernel - Re: [PATCH v5 3/3] Documentation:ABI:testing:admv1013: add ABI docs

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Date:   Sat, 27 Nov 2021 17:13:46 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Antoniu Miclaus <antoniu.miclaus@...log.com>
Cc:     <robh+dt@...nel.org>, <linux-iio@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/3] Documentation:ABI:testing:admv1013: add ABI docs

On Tue, 23 Nov 2021 13:53:36 +0200
Antoniu Miclaus <antoniu.miclaus@...log.com> wrote:

> Add documentation for the use of the Local Oscillator Feedthrough Offset
> calibration.
> 
> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>

Hi Antoniu

Nearly there, but I think the naming isn't quite consistent with normal ABI
and thinking on it a little more, not sure the freq_mode stuff should be
userspace controllable as it will be reflected in the wiring.

Thanks,

Jonathan

> ---
> changes in v5:
>  - rework the custom device attributes based on the feedback received in v4
>  - add frequency translation modes custom attributes.
>  .../testing/sysfs-bus-iio-frequency-admv1013  | 55 +++++++++++++++++++
>  1 file changed, 55 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-frequency-admv1013
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-frequency-admv1013 b/Documentation/ABI/testing/sysfs-bus-iio-frequency-admv1013
> new file mode 100644
> index 000000000000..3ff80909f007
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-frequency-admv1013
> @@ -0,0 +1,55 @@
> +What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage0-1_phase_i

So why phase_i, rather than i_phase?

My logic is that 0-1 is the channel index, i it he modifier and phase is the info_mask element
saying what we are actually modifying about this channel.

So much as we'd have in_accel0_x_scale as with 0 as the index, x as the modifier and 
scale as the 'what' about the channel, the ordering should be the other way around to
what you have.  I and Q are defined as modifiers already so we should remain consistent
with that rather than defining a 'what' as phase_i applied to an unmodified channel
which is what i think this currently corresponds to.

> +KernelVersion:
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Read/write raw value for the Local Oscillatior path quadrature I phase shift.

Raw?  Phase is already documented in the main ABI/testing/sysfs-bus-iio documentation as
being in radians.  That needs to be true here as well so we have consistent ABI.

> +
> +What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage0-1_phase_q
> +KernelVersion:
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Read/write raw value for the Local Oscillatior path quadrature Q phase shift.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage0_calibbias_i
> +KernelVersion:
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Read/write raw value for the Local Oscillatior Feedthrough Offset Calibration I Positive
> +		side.

I'd drop the raw from this as well, though calibbias is often unit free so no need to say anything
about units for this one.

> +
> +What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage0_calibbias_q
> +KernelVersion:
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Read/write raw value for the Local Oscillatior Feedthrough Offset Calibration Q Positive
> +		side.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage1_calibbias_i
> +KernelVersion:
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Read/write raw value for the Local Oscillatior Feedthrough Offset Calibration I Negative
> +		side.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltage1_calibbias_q
> +KernelVersion:
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Read/write raw value for the Local Oscillatior Feedthrough Offset Calibration Q Negative
> +		side.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/freq_mode_available
> +KernelVersion:
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Reading this returns the valid values that can be written to the freq_mode attribute.

Silly question.  How is this the mode of the 'frequency'.  IIRC it's the type of input signal
being provided.   Speaking of which, this is a characteristic of the wiring so I think
this is something that should be in DT unless I'm missing something and should not
be in the control of userspace... (hopefully I didn't say the other way around in an earlier review!)

> +
> +		- if -> Intermediate Frequency
> +		- iq -> Quadrature I/Q mode.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/freq_mode
> +KernelVersion:
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		This attribute configures the frequency mode.
> +		Reading returns the actual mode.