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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 <greg@kroah.com> wrote:
    >>>
    >>>> From: Dean Anderson <dean@sensoray.com>
    >>>>
    >>>>
    >> <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
    V4L2_PIX_FMT_YUV422P.

    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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