Re: Add a "enable" sysfs attribute to the pci devices to allow userspace (Xorg) to enable devices without doing foul direct access

[Bjorn Helgaas]

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.
> >
> > Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> > CC: Peter Jones <pjones@xxxxxxxxxx>
> > CC: Dave Airlie <airlied@xxxxxxxx>
> 
> ACK
> 
> 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 sysfs "enable" patch seems like goodness.

But I hope that when X uses this, it only enables & disables VGA
devices it's actually using.  In the past, it seems like X has
blindly disabled *all* VGA devices in the system, even though
they might be in use by another X server.  I'm sure that's all
well-understood and cleaned up now; just wanted to make sure
this nightmare didn't recur.
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