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Message-ID: <CAJZ5v0hgOxOFA+LBNm+n3BVhuJOYD4F5LBj2BQA7fwLDAtcD=g@mail.gmail.com>
Date: Wed, 1 Oct 2025 11:30:30 +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,
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,
On Wed, Oct 1, 2025 at 1:08 AM Pin-yen Lin <treapking@...omium.org> wrote:
>
> 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?
Yes, it was on the bleeding-edge branch for CI build testing coverage.
It has been added to the linux-next branch now.
Thanks!
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