linux-kernel - Re: [PATCH v2 1/3] hwmon: (pmbus) Add driver for Delta DPS-920AB PSU

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Date:   Fri, 4 Jun 2021 05:38:29 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Robert Marko <robert.marko@...tura.hr>
Cc:     robh+dt@...nel.org, jdelvare@...e.com, corbet@....net,
        linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, trivial@...nel.org,
        Jonathan.Cameron@...wei.com, alexandre.belloni@...tlin.com,
        sst@...zta.fm, krzk@...nel.org, alexandru.ardelean@...log.com,
        devicetree@...r.kernel.org, Luka Perkov <luka.perkov@...tura.hr>,
        jmp@...phyte.org, Paul Menzel <pmenzel@...gen.mpg.de>,
        Donald Buczek <buczek@...gen.mpg.de>
Subject: Re: [PATCH v2 1/3] hwmon: (pmbus) Add driver for Delta DPS-920AB PSU

On Fri, Jun 04, 2021 at 02:16:02PM +0200, Robert Marko wrote:
[ ... ]
> >
> > > +}
> > > +
> > > +static int dps920ab_write_word_data(struct i2c_client *client, int page, int reg,
> > > +                                 u16 word)
> > > +{
> > > +     int ret;
> > > +
> > > +     /*
> > > +      * This masks commands which are not supported.
> > > +      * PSU only has one R/W register and that is
> > > +      * for the fan.
> > > +      */
> > > +     switch (reg) {
> > > +     case PMBUS_FAN_COMMAND_1:
> > > +             break;
> > > +     default:
> > > +             ret = -ENODATA;
> > > +     }
> > > +
> >
> > Does this work ? It is the wrong error message for a failed write;
> > it should probably return -EACCES.
> 
> It appears to work fine, I was looking at other drivers, and all of them
> use -ENODATA for unsupported word registers.

No. They return -ENODATA to tell the PMBus core to use standard PMBus
access functions, ie to handle the access in the core. Please see
_pmbus_write_word_data().

Guenter