linux-kernel - Re: [PATCH] USB: Prevent xhci from resuming root hub during suspend entrance

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Message-ID: <b16e2b38-e9f8-43af-9df0-0510895c02ee@rowland.harvard.edu>
Date: Fri, 10 Jan 2025 10:44:52 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: "Yo-Jung (Leo) Lin" <leo.lin@...onical.com>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, pavel@....cz,
	len.brown@...el.com, bhelgaas@...gle.com, duanchenghao@...inos.cn,
	dlemoal@...nel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	hdegoede@...hat.com
Subject: Re: [PATCH] USB: Prevent xhci from resuming root hub during suspend
 entrance

On Fri, Jan 10, 2025 at 04:44:10PM +0800, Yo-Jung (Leo) Lin wrote:
> The commit d9b4067aef50 ("USB: Fix the issue of task recovery failure
> caused by USB status when S4 wakes up") fixed an issue where if an USB
> port change happens during the entering steps of hibernation, xhci driver
> would attempt to resume the root hub, making the hibernation fail.
> 
> System-wide suspend may fail due to the same reason, but this hasn't been
> addressed yet. This has been found on HP ProOne 440[1], as well as on
> some newer Dell all-in-one models. When suspend fails due to this reason,
> the kernel would show the following messages:

I believe this problem was discussed on the mailing list before, and it 
turned out that the issue was caused by a bug in the xhci-hcd driver, 
not a bug in the USB core.

Basically, suspend is _supposed_ to fail if a wakeup event occurs while 
the suspend is in progress.  As I recall, the bug in xhci-hcd was that 
it treats some non-wakeup events as if they were wakeup events.

In particular, a port change on the root hub should be treated as a 
wakeup event if and only if the root hub is enabled for wakeup.  Does 
xhci-hcd check for this before failing the suspend?

This reasoning shows that your proposed fix is incorrect.

Alan Stern