linux-kernel - Re: [PATCH v7 1/3] PM: wakeup: Add routine to help fetch wakeup source object.

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Date:   Mon, 21 Oct 2019 10:38:07 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ran Wang <ran.wang_1@....com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Rob Herring <robh+dt@...nel.org>, Li Yang <leoyang.li@....com>,
        Mark Rutland <mark.rutland@....com>,
        Pavel Machek <pavel@....cz>, Li Biwen <biwen.li@....com>,
        Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v7 1/3] PM: wakeup: Add routine to help fetch wakeup
 source object.

On Mon, Oct 21, 2019 at 5:49 AM Ran Wang <ran.wang_1@....com> wrote:
>
> Some user might want to go through all registered wakeup sources
> and doing things accordingly. For example, SoC PM driver might need to
> do HW programming to prevent powering down specific IP which wakeup
> source depending on. So add this API to help walk through all registered
> wakeup source objects on that list and return them one by one.
>
> Signed-off-by: Ran Wang <ran.wang_1@....com>
> Tested-by: Leonard Crestez <leonard.crestez@....com>
> ---
> Change in v7:
>         - Remove define of member *dev in wake_irq to fix conflict with commit
>         c8377adfa781 ("PM / wakeup: Show wakeup sources stats in sysfs"), user
>         will use ws->dev->parent instead.
>         - Remove '#include <linux/of_device.h>' because it is not used.
>
> Change in v6:
>         - Add wakeup_source_get_star() and wakeup_source_get_stop() to aligned
>         with wakeup_sources_stats_seq_start/nex/stop.
>
> Change in v5:
>         - Update commit message, add decription of walk through all wakeup
>         source objects.
>         - Add SCU protection in function wakeup_source_get_next().
>         - Rename wakeup_source member 'attached_dev' to 'dev' and move it up
>         (before wakeirq).
>
> Change in v4:
>         - None.
>
> Change in v3:
>         - Adjust indentation of *attached_dev;.
>
> Change in v2:
>         - None.
>
>  drivers/base/power/wakeup.c | 37 +++++++++++++++++++++++++++++++++++++
>  include/linux/pm_wakeup.h   |  3 +++
>  2 files changed, 40 insertions(+)
>
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index 5817b51..dee1b09 100644
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -248,6 +248,43 @@ void wakeup_source_unregister(struct wakeup_source *ws)
>  EXPORT_SYMBOL_GPL(wakeup_source_unregister);
>
>  /**
> + * wakeup_source_get_star - Begin a walk on wakeup source list

The "get" in the name suggests acquiring a reference of some kind
which doesn't happen here.

What about renaming it to wakeup_sources_walk_start()?

> + * @srcuidx: Lock index allocated for this caller.
> + */
> +struct wakeup_source *wakeup_source_get_start(int *srcuidx)

I don't quite like the calling convention here with passing an int
pointer to get the SRCU index back.

What about splitting this into, say, wakeup_sources_read_lock() (that
will return the SRCU index) and wakeup_sources_walk_start() (that will
return the first list entry)?

Then, you could do something like

idx = wakeup_sources_read_lock();

ws = wakeup_sources_walk_start();
while (ws) {

        stuff

        ws = wakeup_sources_walk_next();
}

wakeup_sources_read_unlock(idx);

Or even define for_each_wakeup_source(ws) as

    for (ws = wakeup_sources_walk_start(); ws; ws = wakeup_sources_walk_next())

and use that under a _read_lock()/_read_unlock() pair?