linux-kernel - Re: [PATCH v10 7/7] at24: Support probing while off

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Message-ID: <20210209165418.GG32460@paasikivi.fi.intel.com>
Date:   Tue, 9 Feb 2021 18:54:18 +0200
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rajmohan Mani <rajmohan.mani@...el.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Chiranjeevi Rapolu <chiranjeevi.rapolu@...el.com>,
        Hyungwoo Yang <hyungwoo.yang@...el.com>,
        linux-media <linux-media@...r.kernel.org>
Subject: Re: [PATCH v10 7/7] at24: Support probing while off

On Tue, Feb 09, 2021 at 05:42:45PM +0100, Rafael J. Wysocki wrote:
> On Tue, Feb 9, 2021 at 5:23 PM Sakari Ailus
> <sakari.ailus@...ux.intel.com> wrote:
> >
> > Hi Bartosz, Rafael,
> >
> > On Tue, Feb 09, 2021 at 04:49:37PM +0100, Bartosz Golaszewski wrote:
> > > On Mon, Feb 8, 2021 at 5:54 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > > >
> > > > On Mon, Feb 8, 2021 at 5:44 PM Bartosz Golaszewski
> > > > <bgolaszewski@...libre.com> wrote:
> > > > >
> > > > > On Fri, Feb 5, 2021 at 2:25 PM Sakari Ailus
> > > > > <sakari.ailus@...ux.intel.com> wrote:
> > > > > >
> > > > > > In certain use cases (where the chip is part of a camera module, and the
> > > > > > camera module is wired together with a camera privacy LED), powering on
> > > > > > the device during probe is undesirable. Add support for the at24 to
> > > > > > execute probe while being powered off. For this to happen, a hint in form
> > > > > > of a device property is required from the firmware.
> > > > > >
> > > > > > Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > > > > > Reviewed-by: Tomasz Figa <tfiga@...omium.org>
> > > > > > ---
> > > > >
> > > > > I'll ack this but I still claim that the name
> > > > > acpi_dev_state_low_power() is super misleading for this use-case and
> > > > > I've been saying that for 10 versions now with everyone just ignoring
> > > > > my remarks. :/
> > > >
> > > > Well, the function in question simply checks if the current ACPI power
> > > > state of the device is different from "full power", so its name
> > > > appears to be quite adequate to me.
> > > >
> > > > If the way in which it is used is confusing, though, I guess
> > > > explaining what's going on would be welcome.
> > > >
> > >
> > > Yes, I have explained it multiple time already - last time at v9 of this series:
> > >
> > >     https://www.spinics.net/lists/kernel/msg3816807.html
> >
> > How about adding this to the description of acpi_dev_state_low_power():
> >
> > -----------8<--------------
> >  * This function is intended to be used by drivers to tell whether the device
> >  * is in low power state (D1--D3cold) in driver's probe or remove function. See
> >  * Documentation/firmware-guide/acpi/low-power-probe.rst for more information.
> > -----------8<--------------
> 
> This information is already there in the kerneldoc description of that
> function AFAICS.

Ok, the D states are mentioned already. But how to use it is not, nor
there's a reference to the ReST file. I think that wouldn't hurt.

> 
> I was thinking about adding an explanation comment to the caller.

I think it'd be best if the function name would convey that without a
comment that should then be added to all callers. How about calling the
function e.g. acpi_dev_state_d0() and negating the return value? The D0
state is well defined and we could do this without adding new terms.

-- 
Sakari Ailus