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

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Ricardo Ribalda <ribalda@chromium.org>
Cc: Oliver Neukum <oneukum@suse.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	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
Subject: Re: [PATCH v4] media: ucvideo: Add quirk for Logitech Rally Bar
Date: Fri, 22 Mar 2024 13:57:34 +0200	[thread overview]
Message-ID: <20240322115734.GB31979@pendragon.ideasonboard.com> (raw)
In-Reply-To: <CANiDSCsqER=3OqzxRKYR_vs4as5aO1bfSXmFJtNmzw1kznd_wQ@mail.gmail.com>

On Thu, Feb 29, 2024 at 05:57:38PM +0100, Ricardo Ribalda wrote:
> Oliver, friendly ping

Seconded :-) We can help with the implementation, but we would like your
guidance on the direction you think this should take.

> On Mon, 19 Feb 2024 at 16:13, Ricardo Ribalda wrote:
> >
> > Hi Oliver
> >
> > Would you prefer a version like this?
> >
> > https://lore.kernel.org/all/20231222-rallybar-v2-1-5849d62a9514@chromium.org/
> >
> > If so I can re-submit a version with the 3 vid/pids.  Alan, would you
> > be happy with that?
> >
> > Regards!
> >
> > On Tue, 13 Feb 2024 at 11:47, Laurent Pinchart wrote:
> > > On Mon, Feb 12, 2024 at 02:04:31PM -0500, Alan Stern wrote:
> > > > On Mon, Feb 12, 2024 at 01:22:42PM +0100, Oliver Neukum wrote:
> > > > > 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.
> > > >
> > > > Not necessarily.  If the driver knows that one of these devices may
> > > > already have been suspend and resumed, it can issue its own preemptive
> > > > reset at probe time.
> > > >
> > > > > 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.
> > > >
> > > > That's a separate issue, with its own list of potential problems.
> > > >
> > > > > I am sorry, but it seems to me that the exceptions need
> > > > > to go into usbcore.
> > > >
> > > > If we do then we may want to come up with a better scheme for seeing
> > > > which devices need to have a quirk flag set.  A static listing probably
> > > > won't be good enough; the decision may have to be made dynamically.
> > >
> > > I don't mind either way personally. Oliver, could you try to find a good
> > > solution with Ricardo ? I'll merge the outcome.

-- 
Regards,

Laurent Pinchart