Received-SPF: pass (google.com: domain of linux-kernel+bounces-61540-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Message-ID: <ca89eb86-a566-422c-9448-d8d5254d54b8@suse.com>
Date: Mon, 12 Feb 2024 13:22:42 +0100
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v4] media: ucvideo: Add quirk for Logitech Rally Bar
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
 Ricardo Ribalda <ribalda@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Alan Stern <stern@rowland.harvard.edu>,
 Mauro Carvalho Chehab <mchehab@kernel.org>, linux-usb@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
 stable@vger.kernel.org
References: <20240108-rallybar-v4-1-a7450641e41b@chromium.org>
 <20240204105227.GB25334@pendragon.ideasonboard.com>
Content-Language: en-US
From: Oliver Neukum <oneukum@suse.com>
In-Reply-To: <20240204105227.GB25334@pendragon.ideasonboard.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit

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