linux-kernel - Re: [PATCH 3/3] Documentation: ABI: sysfs-driver-regulator-output

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Date:   Sun, 3 Sep 2023 15:04:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Zev Weiss <zev@...ilderbeest.net>
Cc:     Naresh Solanki <naresh.solanki@...ements.com>, broonie@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] Documentation: ABI: sysfs-driver-regulator-output

On Fri, Sep 01, 2023 at 02:13:23AM -0700, Zev Weiss wrote:
> Adding Greg re: sysfs ABI design...
> 
> On Thu, Aug 31, 2023 at 05:14:10AM PDT, Naresh Solanki wrote:
> > Adds sysfs-driver-regulator-output
> > 
> > Signed-off-by: Naresh Solanki <Naresh.Solanki@...ements.com>
> > ---
> > .../ABI/testing/sysfs-driver-regulator-output         | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> > create mode 100644 Documentation/ABI/testing/sysfs-driver-regulator-output
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-driver-regulator-output b/Documentation/ABI/testing/sysfs-driver-regulator-output
> > new file mode 100644
> > index 000000000000..f9b0a8f810fa
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-driver-regulator-output
> > @@ -0,0 +1,11 @@
> > +What:		/sys/bus/platform/drivers/regulator-output/*/events
> > +Date:		August 2023
> > +Description:	Provided regulator events.
> > +
> > +		Read provides various events the regulator associated with the
> > +		driver has encountered. All REGULATOR_EVENT_* are
> > +		defined in include/uapi/linux/regulator.h
> > +
> > +		e.g.
> > +		cat /sys/bus/platform/drivers/regulator-output/ssb_rssd32/events
> > +		0x0
> 
> If we really are going to proceed with a "read with side-effects"
> (clear-on-read) design, that should absolutely be loudly and clearly
> documented, since it's very different from how sysfs files typically work
> and hence a somewhat glaring principle-of-least-surprise violation.  Also,
> since from the code it looks like it's intended to be used via poll(2), that
> should be described here as well.

Poll?  Ick, but that can happen.

But yes, reading a sysfs should almost never cause a side affect at all.

But what do you mean by "clear events?"  sysfs is only "one value per
file", so you are only returning a single event, right?  It can't be a
list of events, sorry, that's not ok, use a different api for that
please (like a char device node.)

thanks,

greg k-h