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SubjectRe: [v4l-dvb-maintainer] [PATCH] USB: add Sensoray 2255 v4l driver
Trent Piepho wrote:
> On Wed, 14 May 2008, Greg KH wrote:
>> On Thu, May 15, 2008 at 03:17:42AM +0200, Markus Rechberger wrote:
>>> Hi Dean, Greg,
>> Adding dean to the cc: line... :)
>>> On 5/14/08, Greg KH <> wrote:
>>>> From: Dean Anderson <>
>> <big patch snipped>
>>> Why do you do those conversions in kernelspace?
>>> ffmpeg/libswscale has optimized code for colourspace conversions.
>>> I know a few drivers do that in kernelspace but it's way more flexible
>>> in userspace and depending on the optimization requires less CPU
>>> power.
>> I thought they were there as needed by some V4L1 applications, but that
>> code was recently removed by Dean I think. If they don't need to be
>> there, and userspace apps can properly handle the different colorspace,
>> then I'll be glad to remove them.
> Virtually all apps (V4L1 & 2) can handle YUV and RGB colorspaces.
> Certainly all the major ones do and all the major libraries as well.
> The problem is when the device only supports some vendor specific or
> otherwise very uncommon format. In that case not doing the conversion in
> the kernel means the device won't work with any existing software without
> patches. In this case, while it's not "the right way", drivers often end
> up including an in kernel conversion for pragmatic reasons.
> This was a problem with the bayer format, but now userspace support for
> that format is more common.

I agree the conversions don't belong in a driver. For the record, the
following are done in the 2255 hardware: V4L2_PIX_FMT_GREY and

Since planar YUV formats such as V4L2_PIX_FMT_YUV422P are still not that
well supported, is it possible to keep at least one packed YUV
format(V4L2_PIX_FMT_YUYV) in the driver? If not, let me know. I will
strongly suggest that the hardware Engineers add YUY2 or YUYV on board
in the DSP firmware. Thanks, Dean

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