linux-kernel - Re: [PATCH v3] usb: vhci-hcd: Prevent suspending virtually attached devices

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Message-ID: <71b47ce7-a799-42f1-acc7-e59e6ce13884@collabora.com>
Date: Wed, 24 Sep 2025 20:01:55 +0300
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Valentina Manea <valentina.manea.m@...il.com>,
 Shuah Khan <shuah@...nel.org>, Hongren Zheng <i@...ithal.me>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Brian G. Merrell" <bgmerrell@...ell.com>
Cc: kernel@...labora.com, Greg Kroah-Hartman <gregkh@...e.de>,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] usb: vhci-hcd: Prevent suspending virtually attached
 devices

Hi,

On 9/2/25 3:15 PM, Cristian Ciocaltea wrote:
> The VHCI platform driver aims to forbid entering system suspend when at
> least one of the virtual USB ports are bound to an active USB/IP
> connection.
> 
> However, in some cases, the detection logic doesn't work reliably, i.e.
> when all devices attached to the virtual root hub have been already
> suspended, leading to a broken suspend state, with unrecoverable resume.
> 
> Ensure the virtually attached devices do not enter suspend by setting
> the syscore PM flag.  Note this is currently limited to the client side
> only, since the server side doesn't implement system suspend prevention.
> 
> Fixes: 04679b3489e0 ("Staging: USB/IP: add client driver")
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
> ---
> The USB/IP Virtual Host Controller (VHCI) platform driver is expected to
> prevent entering system suspend when at least one remote device is
> attached to the virtual USB root hub.
> 
> However, in some cases, the detection logic for active USB/IP
> connections doesn't seem to work reliably, e.g. when all devices
> attached to the virtual hub have been already suspended.  This will
> normally lead to a broken suspend state, with unrecoverable resume.
> 
> The first patch of the series provides a workaround to ensure the
> virtually attached devices do not enter suspend.  Note this is currently
> limited to the client side (vhci_hcd) only, since the server side
> (usbip_host) doesn't implement system suspend prevention.
> 
> IMPORTANT:
> 
> Please note commit aa7a9275ab81 ("PM: sleep: Suspend async parents after
> suspending children") from v6.16-rc1 introduced a regression which
> breaks the suspend cancellation and hangs the system.
> 
> A fix [1] has been already provided, which also landed soon after in
> v6.16-rc7 under commit ebd6884167ea ("PM: sleep: Update power.completion
> for all devices on errors").
> 
> [1] https://lore.kernel.org/all/6191258.lOV4Wx5bFT@rjwysocki.net/
> ---
> Changes in v3:
> - Moved all driver cleanup patches to a separate series:
>   https://lore.kernel.org/all/20250902-vhci-hcd-cleanup-v1-0-1d46247cb234@collabora.com/
> - Replaced FIXME with NOTE in the new comment block, as it refers to a
>   potential cleanup of redundant code rather than addressing a
>   functional issue
> - Rebased remaining patch onto next-20250902
> - Link to v2: https://lore.kernel.org/r/20250726-vhci-hcd-suspend-fix-v2-0-189266dfdfaa@collabora.com

Just a kind reminder in case there's still a chance to get this and/or the
cleanup patches queued for v6.18.

Thanks,
Cristian