Message-ID: <alpine.LNX.2.00.1108101534370.25232@banach.math.auburn.edu>
Date:	Wed, 10 Aug 2011 15:39:50 -0500 (CDT)
From:	Theodore Kilgore <kilgota@...ach.math.auburn.edu>
To:	Mauro Carvalho Chehab <mchehab@...radead.org>
cc:	Alan Stern <stern@...land.harvard.edu>,
	Hans de Goede <hdegoede@...hat.com>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Greg KH <greg@...ah.com>, linux-usb@...r.kernel.org,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	libusb-devel@...ts.sourceforge.net, Alexander Graf <agraf@...e.de>,
	Gerd Hoffmann <kraxel@...hat.com>, hector@...cansoft.com,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>,
	pbonzini@...hat.com, Anthony Liguori <aliguori@...ibm.com>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Oliver Neukum <oliver@...kum.org>, Felipe Balbi <balbi@...com>,
	Clemens Ladisch <clemens@...isch.de>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Adam Baker <linux@...er-net.org.uk>
Subject: Re: USB mini-summit at LinuxCon Vancouver



On Wed, 10 Aug 2011, Mauro Carvalho Chehab wrote:

> Em 10-08-2011 15:33, Theodore Kilgore escreveu:
> 
> > Hans seems to have argued cogently for doing all of this in the kernel and 
> > for abandoning the usbfs-based drivers for these particular drivers for 
> > dual-mode cameras and, I would conjecture, for drivers for dual-mode 
> > hardware in general. Therefore, I anticipate that he won't like that very 
> > much.
> > 
> > My position:
> > 
> > I do not have preconceptions about how the problem gets handled, and at 
> > this point I remain agnostic and believe that all approaches ought to be 
> > carefully analysed. I can imagine, abstractly, that things like this 
> > could be handled by
> > 
> > -- moving all basic functionality to the kernel, and fixing the 
> > relevant libgphoto2 drivers to look to the kernel instead of to libusb. 
> > (What Hans argues for, and I am not opposed if his arguments convince 
> > other concerned parties)
> 
> Not looking on the amount of work to be done, I think that this would
> give better results, IMO.

Okay. I would guess that I am one of the guys who gets to do the work, 
though.

> 
> > -- doing some kind of patch job to make current arrangement somehow to 
> > work better (this seems to be the position of Adam Baker; I do share
> > the skepticism Hans has expressed about how well this could all be 
> > pasted together)
> 
> Adam Baker's proposal of a locking between usbfs and the kernel driver seems
> to be interesting, but, as he pointed, there are some side effects to consider,
> like suspend/resume, PM, etc.
> 
> > -- doing something like the previous, but also figuring out how to bring 
> > udev rules into play, which would make it all work better (just tossing 
> > this one in, for laughs, but who knows someone might like it)
> 
> I don't think this is a good alternative.

I was trying to mention all alternatives. I should have also mentioned 
"leave things the way they are" but that is certainly out the window.

> 
> > -- moving the kernel webcam drivers out of the kernel and doing with these 
> > cameras _everything_ including webcam function through libusb. I myself do 
> > not have the imagination to be able to figure out how this could be done 
> > without a rather humongous amount of work (for example, which streaming 
> > apps that are currently available would be able to live with this?) but 
> > unless I misunderstand what he was saying, Greg K-H seems to think that 
> > this would be the best thing to do.
> 
> I also don't think that this a good alternative. As Hans V. pointed, one of
> our long term targets is to create per-sensor I2C drivers that are independent
> from the bridges. Also, moving it to userspace would require lots of work
> with the duplication of V4L and gspca core into userspace for the devices
> that would be moved, and may have some performance impacts.

A good argument, though it probably does not affect the devices on my list 
one way or the other. 

> 
> > Which one of these possibile approaches gets adopted is a policy issue 
> > which I would consider is ultimately way above my pay grade.
> > 
> > My main motivation for bringing up the issue was to get it to the front 
> > burner so that _something_ gets done. It is a matter which has been left 
> > alone for too long. Therefore, I am very glad that the matter is being 
> > addressed.
> > 
> > Let me add to this that I have gotten permission for time off and for a 
> > expense money which might possibly cover my air fare. I hope to arrive in 
> > Vancouver by sometime on Monday and intend to attend the mini-summit. I 
> > suggest that we get all intersted parties together and figure out what is 
> > the best way to go.
> > 
> > I hope everyone who is actively concerned can meet in Vancouver, and if 
> > all goes well then on Monday as well as Tuesday. I can hang around for 
> > another day or two after Tuesday, but I do not expect to register for 
> > LinuxCon or be involved in it.
> 
> It will be great to have you there for those discussions.

My take on this was that it seems to have become important for me to 
attend, which, frankly, I was not expecting. So thanks for the nice words.

> 
> > When I leave Vancouver I will probably go 
> > to Seattle and spend a couple of days with my oldest son, the musician, 
> > before coming home on the next weekend.
> > 
> > Theodore Kilgore
> 
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