From: Michal Pecio <michal.pecio@gmail.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Jianping Liu <frankljpliu@gmail.com>,
gregkh@linuxfoundation.org, dakr@kernel.org,
shashank.mahadasyam@sony.com, johan@kernel.org,
hadess@hadess.net, frankjpliu@tencent.com, guanyulin@google.com,
gary@garyguo.net, rafael.j.wysocki@intel.com,
linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
Mathias Nyman <mathias.nyman@linux.intel.com>
Subject: Re: [PATCH] usb: core: raise root-hub autosuspend delay to stop a busy-loop
Date: Mon, 2 Nov 2026 14:34:35 +0100 [thread overview]
Message-ID: <20261102143435.044064df.michal.pecio@gmail.com> (raw)
In-Reply-To: <a35865b5-3779-40a4-9a83-8edd797e56b5@rowland.harvard.edu>
On Thu, 29 Oct 2026 22:23:02 -0400, Alan Stern wrote:
> On Wed, Oct 28, 2026 at 12:18:59PM +0800, Jianping Liu wrote:
> > From: Jianping Liu <frankjpliu@tencent.com>
> >
> > hub_probe() sets the hub autosuspend delay to 0. An idle hub is
> > therefore suspended at once, with no waiting time.
> >
> > Suspending the root hub can fail. While a port reports over-current
> > or a connect change, xHCI refuses the bus suspend and returns
> > -EBUSY. usb_runtime_suspend() returns that error. The hub is
> > resumed, and when its status URB completes the same suspend runs
> > again.
Yes, I have seen this ping-ponging before.
>
> Why should root hubs be special? An ordinary hub doesn't refuse to
> suspend because of an over-current or connect change. xhci-hcd ought
> to behave the same way.
IDK what happened there, but we have this:
commit e9fb08d617bfae5471d902112667d0eeb9dee3c4
Author: Mathias Nyman <mathias.nyman@linux.intel.com>
Date: Tue Apr 21 17:08:21 2020 +0300
xhci: prevent bus suspend if a roothub port detected a over-current condition
Suspending the bus and host controller while a port is in a over-current
condition may halt the host.
Also keep the roothub running if over-current is active.
Cc: <stable@vger.kernel.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200421140822.28233-3-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Regards,
Michal
prev parent reply other threads:[~2026-11-02 13:34 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-28 4:18 Jianping Liu
2026-10-30 2:23 ` Alan Stern
2026-11-02 11:25 ` frank jpliu
2026-11-02 13:34 ` Michal Pecio [this message]
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