[PATCH v2 1/2] driver core: Export device_link_flag_is_sync_state_only()

[PATCH v2 1/2] driver core: Export device_link_flag_is_sync_state_only()

[Pin-yen Lin]

Export device_link_flag_is_sync_state_only() for future patches.

Signed-off-by: Pin-yen Lin <treapking@chromium.org>

---

Changes in v2:
- New in v2

 drivers/base/core.c    | 3 ++-
 include/linux/device.h | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index d22d6b23e758..cc6af9b0d59d 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -287,10 +287,11 @@ 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)
+bool device_link_flag_is_sync_state_only(u32 flags)
 {
 	return (flags & ~DL_MARKER_FLAGS) == DL_FLAG_SYNC_STATE_ONLY;
 }
+EXPORT_SYMBOL_GPL(device_link_flag_is_sync_state_only);
 
 /**
  * device_is_dependent - Check if one device depends on another one
diff --git a/include/linux/device.h b/include/linux/device.h
index 0470d19da7f2..e27d0bf7c43d 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1197,6 +1197,7 @@ const char *dev_driver_string(const struct device *dev);
 struct device_link *device_link_add(struct device *consumer,
 				    struct device *supplier, u32 flags);
 void device_link_del(struct device_link *link);
+bool device_link_flag_is_sync_state_only(u32 flags);
 void device_link_remove(void *consumer, struct device *supplier);
 void device_links_supplier_sync_state_pause(void);
 void device_links_supplier_sync_state_resume(void);
-- 
2.51.0.384.g4c02a37b29-goog

[PATCH v2 2/2] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

[Pin-yen Lin]

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.

Use device_link_flag_is_sync_state_only() 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@chromium.org>
---

Changes in v2:
- Update commit message
- Use device_link_flag_is_sync_state_only()

 drivers/base/power/main.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

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

Re: [PATCH v2 1/2] driver core: Export device_link_flag_is_sync_state_only()

[Greg Kroah-Hartman]

On Thu, Sep 11, 2025 at 07:16:02PM +0800, Pin-yen Lin wrote:
> Export device_link_flag_is_sync_state_only() for future patches.

That says what, but not why.  This feels like an odd thing to export,
what should care about this type of thing?  What should a driver do
based on that information?  We need more information here.

thanks,

greg k-h

Re: [PATCH v2 2/2] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

[Greg Kroah-Hartman]

On Thu, Sep 11, 2025 at 07:16:03PM +0800, Pin-yen Lin 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.
> 
> Use device_link_flag_is_sync_state_only() 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@chromium.org>
> ---
> 
> Changes in v2:
> - Update commit message
> - Use device_link_flag_is_sync_state_only()
> 
>  drivers/base/power/main.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> 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);

The way you use this new function does not require it to have been
exported to modules :(

thanks,

greg k-h

Re: [PATCH v2 2/2] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

[Rafael J. Wysocki]

On Thu, Sep 11, 2025 at 2:28 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Thu, Sep 11, 2025 at 07:16:03PM +0800, Pin-yen Lin 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.
> >
> > Use device_link_flag_is_sync_state_only() 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@chromium.org>
> > ---
> >
> > Changes in v2:
> > - Update commit message
> > - Use device_link_flag_is_sync_state_only()
> >
> >  drivers/base/power/main.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > 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);
>
> The way you use this new function does not require it to have been
> exported to modules :(

Also, I'd just make it non-static (without exporting it to modules)
and use it in the same patch because the new usage is the reason for
exporting.

Re: [PATCH v2 1/2] driver core: Export device_link_flag_is_sync_state_only()

[Rafael J. Wysocki]

On Thu, Sep 11, 2025 at 1:21 PM Pin-yen Lin <treapking@chromium.org> wrote:
>
> Export device_link_flag_is_sync_state_only() for future patches.
>
> Signed-off-by: Pin-yen Lin <treapking@chromium.org>
>
> ---
>
> Changes in v2:
> - New in v2
>
>  drivers/base/core.c    | 3 ++-
>  include/linux/device.h | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index d22d6b23e758..cc6af9b0d59d 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -287,10 +287,11 @@ 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)
> +bool device_link_flag_is_sync_state_only(u32 flags)
>  {
>         return (flags & ~DL_MARKER_FLAGS) == DL_FLAG_SYNC_STATE_ONLY;
>  }
> +EXPORT_SYMBOL_GPL(device_link_flag_is_sync_state_only);

As Greg said, this isn't necessary.

>
>  /**
>   * device_is_dependent - Check if one device depends on another one
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 0470d19da7f2..e27d0bf7c43d 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1197,6 +1197,7 @@ const char *dev_driver_string(const struct device *dev);
>  struct device_link *device_link_add(struct device *consumer,
>                                     struct device *supplier, u32 flags);
>  void device_link_del(struct device_link *link);
> +bool device_link_flag_is_sync_state_only(u32 flags);

No, you only need it in drivers/base/base.h

>  void device_link_remove(void *consumer, struct device *supplier);
>  void device_links_supplier_sync_state_pause(void);
>  void device_links_supplier_sync_state_resume(void);
> --