linux-kernel - Re: [PATCH 2/2] watchdog: Add new arm_smc

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Date:   Thu, 20 Feb 2020 07:52:00 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Evan Benn <evanbenn@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Julius Werner <jwerner@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Marcin Juszkiewicz <marcin.juszkiewicz@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Olof Johansson <olof@...om.net>,
        Leonard Crestez <leonard.crestez@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Will Deacon <will@...nel.org>, linux-watchdog@...r.kernel.org,
        Rob Herring <robh@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Clément Péron <peron.clem@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Anson Huang <Anson.Huang@....com>
Subject: Re: [PATCH 2/2] watchdog: Add new arm_smc_wdt watchdog driver

On Thu, Feb 20, 2020 at 05:50:03PM +1100, Evan Benn wrote:
> > > +     if ((int)res->a0 == PSCI_RET_NOT_SUPPORTED)
> > > +             return -ENOTSUPP;
> >
> > -ENODEV would be better here.
> >
> > > +     if ((int)res->a0 == PSCI_RET_INVALID_PARAMS)
> > > +             return -EINVAL;
> > > +     if ((int)res->a0 < 0)
> > > +             return -EIO;
> 
> In fixing this I found drivers/firmware/psci/psci.c:145
> Which also translates psci codes to errno codes, but uses EOPNOTSUPP:
> 
>     switch (errno) {
>     case PSCI_RET_SUCCESS:
>         return 0;
>     case PSCI_RET_NOT_SUPPORTED:
>         return -EOPNOTSUPP;
>     case PSCI_RET_INVALID_PARAMS:
>     case PSCI_RET_INVALID_ADDRESS:
>         return -EINVAL;
>     case PSCI_RET_DENIED:
>         return -EPERM;
>     };
> 
>     return -EINVAL;
> 
> Are these more appropriate?
> 

It is customary for driver probe functions to return -ENODEV if the
device is not supported. I don't see a reason why this driver should
behave any different. "but this other driver does it" is never a good
argument.

Having said that, yet, with the exception of -EOPNOTSUPP the other
return values would be more appropriate.

Guenter