linux-kernel - Re: [PATCH RFC 01/10] PM: runtime: Add helpers to resume consumers

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Message-ID: <CAJZ5v0gFER-nbWpZK6FMDJCXA+iPQUm5DZDAiRY3ahugR2MM=g@mail.gmail.com>
Date: Wed, 26 Mar 2025 20:18:03 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org, 
	Chen-Yu Tsai <wenst@...omium.org>, Lucas Stach <l.stach@...gutronix.de>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, Marek Vasut <marex@...x.de>, 
	Ulf Hansson <ulf.hansson@...aro.org>, Kevin Hilman <khilman@...nel.org>, 
	Fabio Estevam <festevam@...x.de>, Jacky Bai <ping.bai@....com>, Peng Fan <peng.fan@....com>, 
	Shawn Guo <shawnguo@...nel.org>, Shengjiu Wang <shengjiu.wang@....com>, linux-imx@....com, 
	Ian Ray <ian.ray@...ealthcare.com>, Hervé Codina <herve.codina@...tlin.com>, 
	Luca Ceresoli <luca.ceresoli@...tlin.com>, Saravana Kannan <saravanak@...gle.com>
Subject: Re: [PATCH RFC 01/10] PM: runtime: Add helpers to resume consumers

On Wed, Mar 26, 2025 at 7:26 PM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
>
> The runtime PM core currently allows to runtime resume/suspend a device,
> or its suppliers.
>
> Let's make it also possible to runtime resume/suspend consumers.
>
> Consumers and suppliers are seen here through the description made by
> device_links.

It would be good to explain why all of this is needed.

I gather that it is used for resolving some synchronization issues in
the clk framework, but neither the cover letter nor this changelog
explains how it is used.

> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
>  drivers/base/power/runtime.c | 54 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pm_runtime.h   |  2 ++
>  2 files changed, 56 insertions(+)
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 2ee45841486bc73225b3e971164466647b3ce6d3..04bb66c18e3e4a45751fb3f9a6a1267d73757310 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1841,6 +1841,60 @@ void pm_runtime_put_suppliers(struct device *dev)
>         device_links_read_unlock(idx);
>  }
>
> +static void __pm_runtime_get_consumers(struct device *dev)
> +{
> +       struct device_link *link;
> +
> +       list_for_each_entry_rcu(link, &dev->links.consumers, s_node,
> +                               device_links_read_lock_held())
> +               if (link->flags & DL_FLAG_PM_RUNTIME) {
> +                       pm_runtime_get_sync(link->consumer);
> +                       __pm_runtime_get_consumers(link->consumer);
> +               }
> +}
> +
> +/**
> + * pm_runtime_get_consumers - Resume and reference-count consumer devices.
> + * @dev: Supplier device.
> + */
> +void pm_runtime_get_consumers(struct device *dev)
> +{
> +       int idx;
> +
> +       idx = device_links_read_lock();
> +
> +       __pm_runtime_get_consumers(dev);
> +
> +       device_links_read_unlock(idx);
> +}
> +
> +static void __pm_runtime_put_consumers(struct device *dev)
> +{
> +       struct device_link *link;
> +
> +       list_for_each_entry_rcu(link, &dev->links.consumers, s_node,
> +                               device_links_read_lock_held())
> +               if (link->flags & DL_FLAG_PM_RUNTIME) {
> +                       pm_runtime_put(link->consumer);
> +                       __pm_runtime_put_consumers(link->consumer);
> +               }
> +}
> +
> +/**
> + * pm_runtime_put_consumers - Drop references to consumer devices.
> + * @dev: Supplier device.
> + */
> +void pm_runtime_put_consumers(struct device *dev)
> +{
> +       int idx;
> +
> +       idx = device_links_read_lock();
> +
> +       __pm_runtime_put_consumers(dev);
> +
> +       device_links_read_unlock(idx);
> +}
> +
>  void pm_runtime_new_link(struct device *dev)
>  {
>         spin_lock_irq(&dev->power.lock);
> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index d39dc863f612fe18dc34182117f87908d63c8e6d..151c885a3f421f09509232f144618da62297d61d 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -89,6 +89,8 @@ extern u64 pm_runtime_autosuspend_expiration(struct device *dev);
>  extern void pm_runtime_set_memalloc_noio(struct device *dev, bool enable);
>  extern void pm_runtime_get_suppliers(struct device *dev);
>  extern void pm_runtime_put_suppliers(struct device *dev);
> +extern void pm_runtime_get_consumers(struct device *dev);
> +extern void pm_runtime_put_consumers(struct device *dev);
>  extern void pm_runtime_new_link(struct device *dev);
>  extern void pm_runtime_drop_link(struct device_link *link);
>  extern void pm_runtime_release_supplier(struct device_link *link);
>
> --
> 2.48.1
>