linux-kernel - Re: [PATCH v4] media: ucvideo: Add quirk for Logitech Rally Bar

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Message-ID: <ca89eb86-a566-422c-9448-d8d5254d54b8@suse.com>
Date: Mon, 12 Feb 2024 13:22:42 +0100
From: Oliver Neukum <oneukum@...e.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Ricardo Ribalda <ribalda@...omium.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Alan Stern <stern@...land.harvard.edu>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, linux-usb@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v4] media: ucvideo: Add quirk for Logitech Rally Bar

On 04.02.24 11:52, Laurent Pinchart wrote:
> Hi Ricardo,
> 
> Thank you for the patch.

Hi,

sorry for commenting on this late, but this patch has
a fundamental issue. In fact this issue is the reason the
handling for quirks is in usbcore at all.

If you leave the setting/clearing of this flag to a driver you
are introducing a race condition. The driver may or may not be
present at the time a device is enumerated. And you have
no idea how long the autosuspend delay is on a system
and what its default policy is regarding suspending
devices.
That means that a device can have been suspended and
resumed before it is probed. On a device that needs
RESET_RESUME, we are in trouble.
The inverse issue will arise if a device does not react
well to RESET_RESUME. You cannot rule out that a device
that must not be reset will be reset.

I am sorry, but it seems to me that the exceptions need
to go into usbcore.

	Regards
		Oliver