linux-kernel - Re: [PATCH v1 2/2] PM: runtime: Defer suspending suppliers

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Date:   Fri, 19 Mar 2021 14:29:18 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        "elaine.zhang" <zhangqing@...k-chips.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] PM: runtime: Defer suspending suppliers

On Thu, 18 Mar 2021 at 19:15, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Because the PM-runtime status of the device is not updated in
> __rpm_callback(), attempts to suspend the suppliers of the given
> device triggered by the rpm_put_suppliers() call in there may fail.
>
> To fix this (1) modify __rpm_callback() to avoid attempting to
> actually suspend the suppliers, but only decrease their PM-runtime
> usage counters and (2) make rpm_suspend() try to suspend the suppliers
> after changing the device's PM-runtime status, in analogy with the
> handling of the device's parent.
>
> Link: https://lore.kernel.org/linux-pm/CAPDyKFqm06KDw_p8WXsM4dijDbho4bb6T4k50UqqvR1_COsp8g@mail.gmail.com/
> Fixes: 21d5c57b3726 ("PM / runtime: Use device links")
> Reported-by: elaine.zhang <zhangqing@...k-chips.com>
> Diagnosed-by: Ulf Hansson <ulf.hansson@...aro.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Just a minor nitpick, see below. In any case:

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

> ---
>  drivers/base/power/runtime.c |   45 +++++++++++++++++++++++++++++++++++++------
>  1 file changed, 39 insertions(+), 6 deletions(-)
>
> Index: linux-pm/drivers/base/power/runtime.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/runtime.c
> +++ linux-pm/drivers/base/power/runtime.c
> @@ -305,7 +305,7 @@ static int rpm_get_suppliers(struct devi
>         return 0;
>  }
>
> -static void rpm_put_suppliers(struct device *dev)
> +static void __rpm_put_suppliers(struct device *dev, bool try_to_suspend)
>  {
>         struct device_link *link;
>
> @@ -313,10 +313,30 @@ static void rpm_put_suppliers(struct dev
>                                 device_links_read_lock_held()) {
>
>                 while (refcount_dec_not_one(&link->rpm_active))
> -                       pm_runtime_put(link->supplier);
> +                       pm_runtime_put_noidle(link->supplier);
> +
> +               if (try_to_suspend)
> +                       pm_request_idle(link->supplier);
>         }
>  }
>
> +static void rpm_put_suppliers(struct device *dev)
> +{
> +       __rpm_put_suppliers(dev, true);
> +}
> +
> +static void rpm_try_to_suspend_suppliers(struct device *dev)

Maybe "rpm_suspend_suppliers" is sufficient for the name of the
function, but I have no strong opinion.

> +{
> +       struct device_link *link;
> +       int idx = device_links_read_lock();
> +
> +       list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
> +                               device_links_read_lock_held())
> +               pm_request_idle(link->supplier);
> +
> +       device_links_read_unlock(idx);
> +}
> +

[...]

Kind regards
Uffe