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    SubjectRe: Add a "enable" sysfs attribute to the pci devices to allow userspace (Xorg) to enable devices without doing foul direct access
    Date
    On Saturday 29 April 2006 03:04, Dave Airlie wrote:
    > > This patch adds an "enable" sysfs attribute to each PCI device. When read it
    > > shows the "enabled-ness" of the device, but you can write a "0" into it to
    > > disable a device, and a "1" to enable it.
    > >
    > > This later is needed for X and other cases where userspace wants to enable
    > > the BARs on a device (typical example: to run the video bios on a secundary
    > > head). Right now X does all this "by hand" via bitbanging, that's just evil.
    > > This allows X to no longer do that but to just let the kernel do this.

    I'm all in favor of cleaning up X. But making the X code prettier without
    changing the underlying issues of claiming and sharing resources doesn't
    help much. In fact, I suspect the ultimate plan for X does not involve
    an "enable" attribute in sysfs, so this may just introduce ABI cruft that
    will be difficult to remove later.

    > This would allow me to remove the issue in X where loading the DRM at X
    > startup acts differently than loading the DRM before X runs, due to Xs PCI
    > probe running in-between... with this I can just enable all VGA devices
    > and no worry whether they have a DRM or not..

    This seems to be the main justification for the patch. But I don't know
    enough about X and DRM to understand it, or why this patch is the best
    way to solve it.

    I think Jon has a pretty convincing argument, which I *do* understand.
    Can you expand on this justification? Do you envision long-term usage
    of the sysfs "enable" attribute?

    Bjorn
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