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

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Message-ID: <588d2e1f-1cb5-4868-9160-11a36e8640d6@rowland.harvard.edu>
Date: Fri, 22 Mar 2024 10:40:46 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Ricardo Ribalda <ribalda@...omium.org>, Oliver Neukum <oneukum@...e.com>,
  Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
  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 Fri, Mar 22, 2024 at 01:57:34PM +0200, Laurent Pinchart wrote:
> 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.

Thirded  :-)  I want to hear what Oliver thinks about the original 
patch.

Alan Stern

> > 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