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    SubjectRe: radeon-pre-2

    I would like to disagree with you.

    On Fri, 10 Sep 2004, Alan Cox wrote:

    > On Gwe, 2004-09-10 at 23:19, Dave Airlie wrote:
    >> If the kernel developers can address this point I would be most
    >> interested, in fact I don't want to hear any more about sharing lowlevel
    >> VGA device drivers until someone addresses why it is acceptable to have
    >> two separate driver driving the same hardware for video and not for
    >> anything else.. (remembering graphics cards are not-multifunction cards -
    >> like Christoph used as an example before - 2d/3d are not separate
    >> functions...)...
    > We've addressed this before. Zillions of drivers provide multiple
    > functions to multiple higher level subsystems. They don't all have to
    > be compiled together to make it work.
    > 2D and 3D _are_ to most intents and purposes different functions. They
    > are as different as IDE CD and IDE disk if not more so.

    Functions - yes, but they become such only at a higher level. 3d for
    example does not really exist in kernel in any form.

    I would like to see unified fb (or the hardware-specific part of fb) and
    drm for one simple reason that I think you mentioned:

    One driver per device. I.e. one driver per *physical* device.

    Lastly, one point that you appear to have missed: DRM does DMA transfers
    (among everything else). FB sets video modes - i.e. messes with PLL.
    The problem is that there are configurations where messing with PLL while
    a DMA trasfer is active will lock up PCI (or AGP) bus hard.

    For example, a video decoder can be clocked off pixel clock for video pass
    through mode. If we trasfer video data to main RAM at the same time and
    FB gets a command instructing it to change resolution there would be a
    hard lockup.


    Vladimir Dergachev
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