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

[Greg KH <greg@kroah.com>]

On Tue, May 02, 2006 at 10:14:45AM -0600, Bjorn Helgaas wrote:
> 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@linux.intel.com>
> > > CC: Peter Jones <pjones@redhat.com>
> > > CC: Dave Airlie <airlied@linux.ie>
> > 
> > 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.

Hopefully with the recent PCI changes to X, this will not happen.  If it
does, that's a big bug in X :)

thanks,

greg k-h