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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Sat, 7 Oct 2023 12:41:33 +0200
Message-ID: <CAJZ5v0gF0O_d1rjOtiNj5ryXv-PURv0NgiRWyQECZZFcaBEsPQ@mail.gmail.com>
Subject: Re: [PATCH v2 3/6] ACPI: AC: Replace acpi_driver with platform_driver
To:     Andy Shevchenko <andriy.shevchenko@intel.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Michal Wilczynski <michal.wilczynski@intel.com>,
        linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
        nvdimm@lists.linux.dev, rafael.j.wysocki@intel.com,
        lenb@kernel.org, dan.j.williams@intel.com,
        vishal.l.verma@intel.com, ira.weiny@intel.com
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On Sat, Oct 7, 2023 at 9:56 AM Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Fri, Oct 06, 2023 at 09:47:57PM +0200, Rafael J. Wysocki wrote:
> > On Fri, Oct 6, 2023 at 8:33 PM Michal Wilczynski
> > <michal.wilczynski@intel.com> wrote:
>
> ...
>
> > >  struct acpi_ac {
> > >         struct power_supply *charger;
> > >         struct power_supply_desc charger_desc;
> > > -       struct acpi_device *device;
> > > +       struct device *dev;
> >
> > I'm not convinced about this change.
> >
> > If I'm not mistaken, you only use the dev pointer above to get the
> > ACPI_COMPANION() of it, but the latter is already found in _probe(),
> > so it can be stored in struct acpi_ac for later use and then the dev
> > pointer in there will not be necessary any more.
> >
> > That will save you a bunch of ACPI_HANDLE() evaluations and there's
> > nothing wrong with using ac->device->handle.  The patch will then
> > become almost trivial AFAICS and if you really need to get from ac to
> > the underlying platform device, a pointer to it can be added to struct
> > acpi_ac without removing the ACPI device pointer from it.
>
> The idea behind is to eliminate data duplication.

What data duplication exactly do you mean?

struct acpi_device *device is replaced with struct device *dev which
is the same size.  The latter is then used to obtain a struct
acpi_device pointer.  Why is it better to do this than to store the
struct acpi_device itself?