linux-kernel - Re: USB mini-summit at LinuxCon Vancouver

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Date:	Tue, 09 Aug 2011 21:57:35 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Greg KH <greg@...ah.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	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>,
	Theodore Kilgore <kilgota@...ach.math.auburn.edu>,
	Adam Baker <linux@...er-net.org.uk>
Subject: Re: USB mini-summit at LinuxCon Vancouver

Hi,

On 08/09/2011 04:19 PM, Alan Stern wrote:
> On Tue, 9 Aug 2011, Hans de Goede wrote:
>
>> I would really like to see the dual mode camera and TV tuner discussion
>> separated. They are 2 different issues AFAIK.
>>
>> 1) Dual mode cameras:
>>
>> In the case of the dual mode camera we have 1 single device (both at
>> the hardware level and at the logical block level), which can do 2 things,
>> but not at the same time. It can stream live video data from a sensor,
>> or it can retrieve earlier taken pictures from some picture memory.
>>
>> Unfortunately even though these 2 functions live in a single logical block,
>> historically we've developed 2 drivers for them. This leads to fighting
>> over device ownership (surprise surprise), and to me the solution is
>> very clear, 1 logical block == 1 driver.
>
> According to Theodore, we have developed 5 drivers for them because the
> stillcam modes in different devices use four different vendor-specific
> drivers.

Yes, but so the the webcam modes of the different devices, so for
the 5 (not sure if that is the right number) dual-cam mode chipsets
we support there will be 5 drivers, each supporting both the
webcam and the access to pictures stored in memory of the chipset
they support. So 5 chipsets -> 5 drivers each supporting 1 chipset,
and both functions of the single logical device that chipset
represents.

>  Does it really make sense to combine 5 drivers into one?

Right, that is not the plan. The plan is to simply stop having 2 drivers
for 1 logical (and physical) block. So we go from 10 drivers, 5 stillcam
+ 5 webcam, to just 5 drivers. We will also likely be able to share
code between the code for the 2 functionalities for things like generic
set / get register functions, initialization, etc.

Regards,

Hans
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