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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Wed, 12 Aug 2020 20:07:04 +0200
Message-ID: <CAMpxmJWziqW-PiJPSm6aH5aXbYktMJfVjJfvfGxv8fdbWKydqg@mail.gmail.com>
Subject: Re: [PATCH v4 5/6] at24: Support probing while off
To:     Sakari Ailus <sakari.ailus@iki.fi>
Cc:     Sakari Ailus <sakari.ailus@linux.intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        linux-i2c <linux-i2c@vger.kernel.org>,
        Wolfram Sang <wsa@the-dreams.de>, linux-acpi@vger.kernel.org,
        Bingbu Cao <bingbu.cao@intel.com>,
        linux-media <linux-media@vger.kernel.org>,
        Chiranjeevi Rapolu <chiranjeevi.rapolu@intel.com>,
        Hyungwoo Yang <hyungwoo.yang@intel.com>,
        Arnd Bergmann <arnd@arndb.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rajmohan Mani <rajmohan.mani@intel.com>,
        Tomasz Figa <tfiga@chromium.org>
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On Tue, Aug 11, 2020 at 10:00 AM Sakari Ailus <sakari.ailus@iki.fi> wrote:
>
> Hi Bartosz,
>
> On Mon, Aug 10, 2020 at 08:12:00PM +0200, Bartosz Golaszewski wrote:
> > On Mon, Aug 10, 2020 at 10:26 AM Sakari Ailus <sakari.ailus@iki.fi> wro=
te:
> > >
> >
> > [snip]
> >
> > > >
> > > > Rafael: I think that there are two issues with patch 1/5:
> > > > 1. It adds a very specific boolean flag to a structure that's meant=
 to
> > > > be very general. As I pointed out in the i2c patch: at the very lea=
st
> > > > this could be made into an int storing flag values, instead of a
> > > > boolean field. But rather than that - it looks to me more like a
> > > > device (or bus) feature than a driver feature. Is there any ACPI fl=
ag
> > > > we could use to pass this information to the driver model without
> > > > changing the driver structure?
> > >
> > > To my knowledge there isn't. The fact that I=E6=B6=8E devices are pow=
ered on for
> > > probe in ACPI based systems is specific to Linux kernel and not ACPI =
as
> > > such.
> > >
> > > The reason this needs to be in a generic struct is that the device's =
power
> > > state will be changed before any interaction with the driver takes pl=
ace as
> > > it's the I=E6=B6=8E framework that powers on the device.
> > >
> >
> > I'm not sure I'm following. Looking at patch 1/6 struct device already
> > exists so why can't this information be conveyed "per device" as
> > opposed to "per driver"?
>
> It's both driver and device.
>
> Suppose there's no indication of driver support. If you add the property
> telling the device shouldn't be powered on for probe, it won't be. And if
> the driver doesn't support that, probe will fail. That could happen e.g.
> when running an older kernel on a system that happens to specify this
> property for a given device.
>
> You could view this as a driver bug of course. I still think it's better =
to
> make driver support for this explicit, and avoid making this a practical
> problem anywhere.
>

I see. I'm not sure this is the correct solution but let's see what
Wolfram says. From my side: I'd prefer to see the
disable_i2c_core_irq_mapping converted to flags first and then the
flags extended with whatever you need. disable_i2c_core_irq_mapping
could also be removed AFAICT - nobody uses it.

Bart