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 Thursday 04 May 2006 13:11, Arjan van de Ven wrote:
> 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.
> > 
> > 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.
> 
> it goes well beyond X. Things like vbetool need this too to get to the content
> of the rom for example. There are several other such cases...

There's already a "rom" file in sysfs.  Could vbetool and friends
use that?

How do vbetool and X coordinate their usage of "enable"?  What if we
throw an in-kernel VGA driver into the mix?  But I guess Jon has asked
all these questions before; I just didn't get warm fuzzies that there
were safe, maintainable answers.
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