linux-kernel - Re: [PATCH v2 3/6] ACPI: AC: Replace acpi_driver with platform

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Date:   Fri, 6 Oct 2023 21:47:57 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Michal Wilczynski <michal.wilczynski@...el.com>
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        nvdimm@...ts.linux.dev, rafael.j.wysocki@...el.com,
        andriy.shevchenko@...el.com, lenb@...nel.org,
        dan.j.williams@...el.com, vishal.l.verma@...el.com,
        ira.weiny@...el.com
Subject: Re: [PATCH v2 3/6] ACPI: AC: Replace acpi_driver with platform_driver

On Fri, Oct 6, 2023 at 8:33 PM Michal Wilczynski
<michal.wilczynski@...el.com> wrote:
>
> AC driver uses struct acpi_driver incorrectly to register itself. This
> is wrong as the instances of the ACPI devices are not meant to
> be literal devices, they're supposed to describe ACPI entry of a
> particular device.
>
> Use platform_driver instead of acpi_driver. In relevant places call
> platform devices instances pdev to make a distinction with ACPI
> devices instances.
>
> Drop unnecessary casts from acpi_bus_generate_netlink_event() and
> acpi_notifier_call_chain().
>
> Add a blank line to distinguish pdev API vs local ACPI notify function.
>
> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Signed-off-by: Michal Wilczynski <michal.wilczynski@...el.com>
> ---
>  drivers/acpi/ac.c | 70 +++++++++++++++++++++++++----------------------
>  1 file changed, 37 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/acpi/ac.c b/drivers/acpi/ac.c
> index f809f6889b4a..298defeb5301 100644
> --- a/drivers/acpi/ac.c
> +++ b/drivers/acpi/ac.c
> @@ -33,8 +33,9 @@ MODULE_AUTHOR("Paul Diefenbaugh");
>  MODULE_DESCRIPTION("ACPI AC Adapter Driver");
>  MODULE_LICENSE("GPL");
>
> -static int acpi_ac_add(struct acpi_device *device);
> -static void acpi_ac_remove(struct acpi_device *device);
> +static int acpi_ac_probe(struct platform_device *pdev);
> +static void acpi_ac_remove(struct platform_device *pdev);
> +
>  static void acpi_ac_notify(acpi_handle handle, u32 event, void *data);
>
>  static const struct acpi_device_id ac_device_ids[] = {
> @@ -51,21 +52,10 @@ static SIMPLE_DEV_PM_OPS(acpi_ac_pm, NULL, acpi_ac_resume);
>  static int ac_sleep_before_get_state_ms;
>  static int ac_only;
>
> -static struct acpi_driver acpi_ac_driver = {
> -       .name = "ac",
> -       .class = ACPI_AC_CLASS,
> -       .ids = ac_device_ids,
> -       .ops = {
> -               .add = acpi_ac_add,
> -               .remove = acpi_ac_remove,
> -               },
> -       .drv.pm = &acpi_ac_pm,
> -};
> -
>  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.

>         unsigned long long state;
>         struct notifier_block battery_nb;
>  };