linux-kernel - Re: [PATCH] i2c: core: helper function to detect slave mode

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Date:   Thu, 12 Jan 2017 19:01:22 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Vladimir Zapolskiy <vz@...ia.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Luis Oliveira <Luis.Oliveira@...opsys.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-i2c@...r.kernel.org, devicetree <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ramiro.Oliveira@...opsys.com, Joao Pinto <Joao.Pinto@...opsys.com>,
        CARLOS.PALMINHA@...opsys.com
Subject: Re: [PATCH] i2c: core: helper function to detect slave mode

On Sat, 2017-01-07 at 03:24 +0200, Vladimir Zapolskiy wrote:
> On 01/07/2017 02:19 AM, Andy Shevchenko wrote:
> > On Sat, Jan 7, 2017 at 1:43 AM, Vladimir Zapolskiy <vz@...ia.com>
> > wrote:
> > > On 01/07/2017 12:45 AM, Andy Shevchenko wrote:

> > > > +             }
> > > > > > +     } else if (IS_BUILTIN(CONFIG_ACPI) &&
> > > > > > ACPI_HANDLE(dev)) {
> > > > > > +             dev_dbg(dev, "ACPI slave is not supported
> > > > > > yet\n");
> > > > > > +     }
> > > > > 
> > > > > If so, then it might be better to drop else-if stub for now.
> > > > 
> > > > Please, don't.
> > > > 
> > > 
> > > Why do you ask for this stub to be added?
> > 
> > 1. Exactly the reason you asked above. Here is the code which has
> > built differently on different platforms. x86 usually is not using
> > CONFIG_OF, ARM doesn't ACPI (versus ARM64). Check GPIO library for
> > existing examples.
> 
> From the context by the stub I mean dev_dbg() in
> i2c_slave_mode_detect()
> function, I don't see a connection to GPIO library, please clarify.

I agree that is not good proof for using IS_ENABLED/IS_BUILTIN macro.

> > 2. We might add that support later, but here is again, just no-op.
> > 
> > So, what is your strong argument here against that?
> 
> When the support is ready for ACPI case, you'll remove the added
> dev_dbg(), and I don't see a good point by adding it temporarily.

It would remind me to look at it at some point.

> What is wrong with the approach of adding the ACPI case handling
> branch when it is ready and remove any kind of stubs right now?

I will not object. Here is maintainer, let him speak.

> On ACPI platforms the function returns 'false' always, will the
> function work correctly (= corresponding to its description) as is?

Yes.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy