linux-kernel - Re: [PATCH v3 26/27] staging: iio: resolver: ad2s1210: implement fault events

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Date:   Mon, 2 Oct 2023 13:49:51 -0500
From:   David Lechner <dlechner@...libre.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-staging@...ts.linux.dev,
        David Lechner <david@...hnology.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Nuno Sá <nuno.sa@...log.com>,
        Axel Haslam <ahaslam@...libre.com>,
        Philip Molloy <pmolloy@...libre.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 26/27] staging: iio: resolver: ad2s1210: implement
 fault events

On Mon, Oct 2, 2023 at 11:58 AM David Lechner <dlechner@...libre.com> wrote:
>
> On Sat, Sep 30, 2023 at 11:00 AM Jonathan Cameron <jic23@...nel.org> wrote:
> >
> > On Fri, 29 Sep 2023 12:23:31 -0500
> > David Lechner <dlechner@...libre.com> wrote:
> >
> > > From: David Lechner <david@...hnology.com>
> > >
> > > From: David Lechner <dlechner@...libre.com>
> > >
> > > When reading the position and velocity on the AD2S1210, there is also a
> > > 3rd byte following the two data bytes that contains the fault flag bits.
> > > This patch adds support for reading this byte and generating events when
> > > faults occur.
> > >
> > > The faults are mapped to various channels and event types in order to
> > > have a unique event for each fault.
> > >
> > > Signed-off-by: David Lechner <dlechner@...libre.com>
> >
> > Use of x and y modifiers is a little odd.  What was your reasoning?
> > Was it just that there was a X_OR_Y modifier?  If so, don't use that!
> > It seemed like a good idea at the time, but it's not nice to deal with
> > and requires a channel with that modifier to hang the controls off
> > + make sure userspace expects that event code.
>
>
> Regarding the point about "requires a channel with that modifier to
> hang the controls off...". Although that comment was about modifiers,
> does it also apply in general.
>
> There are several fault events that don't have any configurable
> parameters, namely _sine/cosine inputs clipping_ and _velocity exceeds
> max tracking rate_. So there won't be any attributes that contain the
> event specification for those (e.g. no `events/in_angl0_*`
> attributes). It sounds like this would be a problem as well?
>
> Should we consider a IIO_EV_INFO_LABEL so that we can have some sort
> of attribute (namely `events/<dir>_<channel spec>_label`) so that
> userspace can enumerate expected events for non-configurable events?

Well, I didn't think that all the way through before I hit send.
IIO_EV_INFO_LABEL is clearly not the right way to implement a
`events/*_label` attribute, but however we consider going about it,
the point of adding such an attribute was the main idea.