linux-kernel - Re: [PATCH v3] PM: sleep: Don't wait for SYNC_STATE

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Message-ID: <CAJZ5v0iPCt6O4QcFC1BDVtH-zP7g53ngiR3fsd9DNQjejkqj8A@mail.gmail.com>
Date: Fri, 12 Sep 2025 17:41:45 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Pin-yen Lin <treapking@...omium.org>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, Pavel Machek <pavel@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, linux-kernel@...r.kernel.org, 
	Chen-Yu Tsai <wenst@...omium.org>, Hsin-Te Yuan <yuanhsinte@...omium.org>, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

On Fri, Sep 12, 2025 at 4:48 PM Pin-yen Lin <treapking@...omium.org> wrote:
>
> Device links with DL_FLAG_SYNC_STATE_ONLY should not affect suspend
> and resume, and functions like device_reorder_to_tail() and
> device_link_add() doesn't try to reorder the consumers with such flag.
>
> However, dpm_wait_for_consumers() and dpm_wait_for_suppliers() doesn't
> check this flag before triggering dpm_wait, leading to potential hang
> during suspend/resume.
>
> This can be reproduced on MT8186 Corsola Chromebook with devicetree like:
>
> usb-a-connector {
>         compatible = "usb-a-connector";
>         port {
>                 usb_a_con: endpoint {
>                         remote-endpoint = <&usb_hs>;
>                 };
>         };
> };
>
> usb_host {
>         compatible = "mediatek,mt8186-xhci", "mediatek,mtk-xhci";
>         port {
>                 usb_hs: endpoint {
>                         remote-endpoint = <&usb_a_con>;
>                 };
>         };
> };
>
> In this case, the two nodes form a cycle and a SYNC_STATE_ONLY devlink
> between usb_host (supplier) and usb-a-connector (consumer) is created.
>
> Export device_link_flag_is_sync_state_only() and use it to check this in
> dpm_wait_for_consumers() and dpm_wait_for_suppliers() to fix this.
>
> Fixes: 05ef983e0d65a ("driver core: Add device link support for SYNC_STATE_ONLY flag")
> Signed-off-by: Pin-yen Lin <treapking@...omium.org>
> ---
>
> Changes in v3:
> - Squash to one patch and fix the export approach
>
> Changes in v2:
> - Update commit message
> - Use device_link_flag_is_sync_state_only()
>
>  drivers/base/base.h       | 1 +
>  drivers/base/core.c       | 2 +-
>  drivers/base/power/main.c | 6 ++++--
>  3 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 123031a757d9..80415b140ce7 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -248,6 +248,7 @@ void device_links_driver_cleanup(struct device *dev);
>  void device_links_no_driver(struct device *dev);
>  bool device_links_busy(struct device *dev);
>  void device_links_unbind_consumers(struct device *dev);
> +bool device_link_flag_is_sync_state_only(u32 flags);
>  void fw_devlink_drivers_done(void);
>  void fw_devlink_probing_done(void);
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index d22d6b23e758..741aa0571fc7 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -287,7 +287,7 @@ static bool device_is_ancestor(struct device *dev, struct device *target)
>  #define DL_MARKER_FLAGS                (DL_FLAG_INFERRED | \
>                                  DL_FLAG_CYCLE | \
>                                  DL_FLAG_MANAGED)
> -static inline bool device_link_flag_is_sync_state_only(u32 flags)
> +inline bool device_link_flag_is_sync_state_only(u32 flags)

We generally don't use inline without static.  Let the compiler decide
what to do with it.

>  {
>         return (flags & ~DL_MARKER_FLAGS) == DL_FLAG_SYNC_STATE_ONLY;
>  }
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index 2ea6e05e6ec9..73a1916170ae 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -282,7 +282,8 @@ static void dpm_wait_for_suppliers(struct device *dev, bool async)
>          * walking.
>          */
>         list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
> -               if (READ_ONCE(link->status) != DL_STATE_DORMANT)
> +               if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
> +                   !device_link_flag_is_sync_state_only(link->flags))
>                         dpm_wait(link->supplier, async);
>
>         device_links_read_unlock(idx);
> @@ -339,7 +340,8 @@ static void dpm_wait_for_consumers(struct device *dev, bool async)
>          * unregistration).
>          */
>         list_for_each_entry_rcu_locked(link, &dev->links.consumers, s_node)
> -               if (READ_ONCE(link->status) != DL_STATE_DORMANT)
> +               if (READ_ONCE(link->status) != DL_STATE_DORMANT &&
> +                   !device_link_flag_is_sync_state_only(link->flags))
>                         dpm_wait(link->consumer, async);
>
>         device_links_read_unlock(idx);
> --