RE: [PATCH v2 2/3] iio: ABI: add ABI file for the LTC2688 DAC

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> -----Original Message-----
> From: Jonathan Cameron <jic23@xxxxxxxxxx>
> Sent: Sunday, January 16, 2022 1:21 PM
> To: Sa, Nuno <Nuno.Sa@xxxxxxxxxx>
> Cc: linux-iio@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; Rob
> Herring <robh+dt@xxxxxxxxxx>; Lars-Peter Clausen
> <lars@xxxxxxxxxx>; Hennerich, Michael
> <Michael.Hennerich@xxxxxxxxxx>
> Subject: Re: [PATCH v2 2/3] iio: ABI: add ABI file for the LTC2688 DAC
> 
> [External]
> 
> On Sat, 15 Jan 2022 10:27:04 +0100
> Nuno Sá <nuno.sa@xxxxxxxxxx> wrote:
> 
> > Define the sysfs interface for toggle or dither capable channels.
> Dither
> > capable channels will have the extended interface:
> >
> >  * out_voltageY_dither_en
> >  * out_voltageY_dither_raw
> >  * out_voltageY_dither_offset
> >  * out_voltageY_dither_raw_available
> >  * out_voltageY_dither_frequency
> >  * out_voltageY_dither_frequency_available
> >  * out_voltageY_dither_phase
> >  * out_voltageY_dither_phase_available
> >
> > Toggle enabled channels will have:
> >
> >  * out_voltageY_toggle_en
> >  * out_voltageY_raw0
> >  * out_voltageY_raw1
> >  * out_voltageY_symbol
> 
> Maybe worth just stating the normal interface here as well because
> it's not clear from these examples if
> out_voltageY_raw still exists for toggle enabled channels (I'm assuming
> not?)

Yes, it does not exist as It would not make sense :)...

> >
> > Signed-off-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
> ABI seems good to me, just a few comments on details of the
> documentation.
> Thanks,
> 
> Jonathan
> > ---
> >  .../ABI/testing/sysfs-bus-iio-dac-ltc2688     | 80
> +++++++++++++++++++
> >  MAINTAINERS                                   |  1 +
> >  2 files changed, 81 insertions(+)
> >  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-dac-
> ltc2688
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-iio-dac-ltc2688
> b/Documentation/ABI/testing/sysfs-bus-iio-dac-ltc2688
> > new file mode 100644
> > index 000000000000..38d1df81c6dc
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-bus-iio-dac-ltc2688
> > @@ -0,0 +1,80 @@
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_dither_en
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Dither enable. Write 1 to enable dither or 0 to disable it.
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_dither_raw
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		This raw, unscaled value refers to the dither signal
> amplitude.
> > +		The same scale as in out_voltageY_raw applies.
> However, the
> > +		offset might be different as it's always 0 for this
> attribute.
> 
> We'll have to be careful if we ever generalize these docs but what you
> have here
> is fine whilst it applies to just this device.
> 
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_dither_raw_av
> ailable
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Available range for dither raw amplitude values.
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_dither_offset
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Offset applied to out_voltageY_dither_raw. Read only
> attribute
> > +		always set to 0.
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_dither_freque
> ncy
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Sets the dither signal frequency.
> Units.
> 
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_dither_freque
> ncy_available
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Returns the available values for the dither frequency.
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_dither_phase
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Sets the dither signal phase.
> 
> Units.  Radians, or refer to the main _phase docs and say it's the same.
> 
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_dither_phase_
> available
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Returns the available values for the dither phase.
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_toggle_en
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Toggle enable. Write 1 to enable toggle or 0 to disable
> it.
> 
> Say why this is useful (presumably toggle with a clock rather than via
> _symbol)
> 
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_raw0
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		It has the same meaning as out_voltageY_raw. This
> attribute is
> > +		specific to toggle enabled channels and refers to the
> DAC output
> > +		code in INPUT_A. The same scale, offset, etc applies.
> 
> Same as what?
> 
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_raw1
> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Same as out_voltageY_raw0 but referring to the DAC
> output code
> > +		in INPUT_B.
> 
> You could combine this with previous and have two what lines.  Might
> allow
> a slightly more compact clear description.

Did not remembered I could do that...

> 
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/out_voltageY_symbol
> 
> Ah. That answers one of my binding related questions :)  You have
> kept
> software control as an option for toggle.

Yeah... It was your suggestion to expose this one only when no pin is
given in dts 😉.

> > +KernelVersion:	5.17
> > +Contact:	linux-iio@xxxxxxxxxxxxxxx
> > +Description:
> > +		Performs a SW toggle. This attribute is specific to toggle
> > +		enabled channels and allows to toggle between
> out_voltageY_raw
> 
> _raw0
> 
> > +		and out_voltageY_raw1 through software. Writing 0
> will select
> > +		out_voltageY_raw while 1 selects out_voltageY_raw1.
> _raw0

Forgot to change it here and above :/

- Nuno Sá




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