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

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Message-ID: <20250912143911.445452-1-treapking@chromium.org>
Date: Fri, 12 Sep 2025 22:39:07 +0800
From: Pin-yen Lin <treapking@...omium.org>
To: "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>
Cc: linux-kernel@...r.kernel.org,
	Chen-Yu Tsai <wenst@...omium.org>,
	Hsin-Te Yuan <yuanhsinte@...omium.org>,
	linux-pm@...r.kernel.org,
	Pin-yen Lin <treapking@...omium.org>
Subject: [PATCH v3] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

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)
 {
 	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);
-- 
2.51.0.384.g4c02a37b29-goog