linux-kernel - Re: [PATCH v4] PM: sleep: Don't wait for SYNC_STATE

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Message-ID: <CAEXTbpfUEDf_L3wVJEwD=Wjhx05X6Z2F-rbZT5L7vUR8GUAWTQ@mail.gmail.com>
Date: Wed, 1 Oct 2025 07:08:12 +0800
From: Pin-yen Lin <treapking@...omium.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: 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, 
	Hsin-Te Yuan <yuanhsinte@...omium.org>, Chen-Yu Tsai <wenst@...omium.org>, linux-pm@...r.kernel.org
Subject: Re: [PATCH v4] PM: sleep: Don't wait for SYNC_STATE_ONLY device links

Hi Rafael,

On Sat, Sep 27, 2025 at 8:13 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Fri, Sep 26, 2025 at 12:23 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 v4:
> > - Remove inline for device_link_flag_is_sync_state_only()
> >
> > 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..a54ec6df1058 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)
> > +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);
> > --
>
> Rebased on top of linux-pm.git/linux-next and applied as 6.18 material
> with some minor edits in the subject and changelog.
>
> Thanks!

Thanks for updating the commit message and applying the patch.

However, I can't find this patch at
https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/log/?h=linux-next

Did I check the wrong place for this?

Regards,
Pin-yen