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

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Message-ID: <21e8256b-5409-4420-9958-e89b716ddfe8@linuxfoundation.org>
Date: Wed, 24 Sep 2025 14:39:16 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>,
 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,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v3] usb: vhci-hcd: Prevent suspending virtually attached
 devices

On 9/24/25 11:01, Cristian Ciocaltea wrote:
> 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.
> 

Sorry for the delay - it has been crazy few weeks for me.

Acked-by: Shuah Khan <skhan@...uxfoundation.org>

thanks,
-- Shuah