linux-kernel - Re: [PATCH v3 3/6] PM: core: Add EXPORT[_GPL]_SIMPLE_DEV_PM

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Date:   Mon, 10 Jan 2022 13:18:36 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Len Brown <len.brown@...el.com>,
        Pavel Machek <pavel@....cz>, list@...ndingux.net,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Jonathan Cameron <jonathan.cameron@...wei.com>
Subject: Re: [PATCH v3 3/6] PM: core: Add EXPORT[_GPL]_SIMPLE_DEV_PM_OPS macros

On Fri, 7 Jan 2022 at 19:17, Paul Cercueil <paul@...pouillou.net> wrote:
>
> These macros are defined conditionally, according to CONFIG_PM:
> - if CONFIG_PM is enabled, these macros resolve to
>   DEFINE_SIMPLE_DEV_PM_OPS(), and the dev_pm_ops symbol will be
>   exported.
>
> - if CONFIG_PM is disabled, these macros will result in a dummy static
>   dev_pm_ops to be created with the __maybe_unused flag. The dev_pm_ops
>   will then be discarded by the compiler, along with the provided
>   callback functions if they are not used anywhere else.
>
> In the second case, the symbol is not exported, which should be
> perfectly fine - users of the symbol should all use the pm_ptr() or
> pm_sleep_ptr() macro, so the dev_pm_ops marked as "extern" in the
> client's code will never be accessed.
>
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

Clearly this can be useful!

My main concern is rather that the macros become a bit complicated
(for understandable reasons) and that kind of continues while looking
at patch4 and patch5 too. Hopefully that doesn't prevent users from
adopting them, and the current situation deserves improvements, so I
think this is worth a try!

Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>

Kind regards
Uffe


> ---
>
> Notes:
>     v2: Remove useless empty line
>     v3: - Reorder the code to have non-private macros together in the file
>         - Add comment about the necesity to use the new export macro when
>           the dev_pm_ops has to be exported
>
>  include/linux/pm.h | 35 ++++++++++++++++++++++++++++++++---
>  1 file changed, 32 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 8e13387e70ec..8279af2c538a 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -8,6 +8,7 @@
>  #ifndef _LINUX_PM_H
>  #define _LINUX_PM_H
>
> +#include <linux/export.h>
>  #include <linux/list.h>
>  #include <linux/workqueue.h>
>  #include <linux/spinlock.h>
> @@ -357,14 +358,42 @@ struct dev_pm_ops {
>  #define SET_RUNTIME_PM_OPS(suspend_fn, resume_fn, idle_fn)
>  #endif
>
> +#define _DEFINE_DEV_PM_OPS(name, \
> +                          suspend_fn, resume_fn, \
> +                          runtime_suspend_fn, runtime_resume_fn, idle_fn) \
> +const struct dev_pm_ops name = { \
> +       SYSTEM_SLEEP_PM_OPS(suspend_fn, resume_fn) \
> +       RUNTIME_PM_OPS(runtime_suspend_fn, runtime_resume_fn, idle_fn) \
> +}
> +
> +#ifdef CONFIG_PM
> +#define _EXPORT_DEV_PM_OPS(name, suspend_fn, resume_fn, runtime_suspend_fn, \
> +                          runtime_resume_fn, idle_fn, sec) \
> +       _DEFINE_DEV_PM_OPS(name, suspend_fn, resume_fn, runtime_suspend_fn, \
> +                          runtime_resume_fn, idle_fn); \
> +       _EXPORT_SYMBOL(name, sec)
> +#else
> +#define _EXPORT_DEV_PM_OPS(name, suspend_fn, resume_fn, runtime_suspend_fn, \
> +                          runtime_resume_fn, idle_fn, sec) \
> +static __maybe_unused _DEFINE_DEV_PM_OPS(__static_##name, suspend_fn, \
> +                                        resume_fn, runtime_suspend_fn, \
> +                                        runtime_resume_fn, idle_fn)
> +#endif
> +
>  /*
>   * Use this if you want to use the same suspend and resume callbacks for suspend
>   * to RAM and hibernation.
> + *
> + * If the underlying dev_pm_ops struct symbol has to be exported, use
> + * EXPORT_SIMPLE_DEV_PM_OPS() or EXPORT_GPL_SIMPLE_DEV_PM_OPS() instead.
>   */
>  #define DEFINE_SIMPLE_DEV_PM_OPS(name, suspend_fn, resume_fn) \
> -const struct dev_pm_ops name = { \
> -       SYSTEM_SLEEP_PM_OPS(suspend_fn, resume_fn) \
> -}
> +       _DEFINE_DEV_PM_OPS(name, suspend_fn, resume_fn, NULL, NULL, NULL)
> +
> +#define EXPORT_SIMPLE_DEV_PM_OPS(name, suspend_fn, resume_fn) \
> +       _EXPORT_DEV_PM_OPS(name, suspend_fn, resume_fn, NULL, NULL, NULL, "")
> +#define EXPORT_GPL_SIMPLE_DEV_PM_OPS(name, suspend_fn, resume_fn) \
> +       _EXPORT_DEV_PM_OPS(name, suspend_fn, resume_fn, NULL, NULL, NULL, "_gpl")
>
>  /* Deprecated. Use DEFINE_SIMPLE_DEV_PM_OPS() instead. */
>  #define SIMPLE_DEV_PM_OPS(name, suspend_fn, resume_fn) \
> --
> 2.34.1
>