linux-kernel - Re: [PATCH v4 5/6] at24: Support probing while off

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Message-ID: <CAMpxmJUKSR-oCGnV1E5XiAMA2nYBy5f_f8=VSoMn0zf+qF39vg@mail.gmail.com>
Date:   Mon, 10 Aug 2020 20:12:00 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Wolfram Sang <wsa@...-dreams.de>, linux-acpi@...r.kernel.org,
        Bingbu Cao <bingbu.cao@...el.com>,
        linux-media <linux-media@...r.kernel.org>,
        Chiranjeevi Rapolu <chiranjeevi.rapolu@...el.com>,
        Hyungwoo Yang <hyungwoo.yang@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rajmohan Mani <rajmohan.mani@...el.com>,
        Tomasz Figa <tfiga@...omium.org>
Subject: Re: [PATCH v4 5/6] at24: Support probing while off

On Mon, Aug 10, 2020 at 10:26 AM Sakari Ailus <sakari.ailus@....fi> wrote:
>

[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 least
> > 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 flag
> > 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 I²C devices are powered 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 place as
> it's the I²C 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"?

[snip]

Bartosz