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

[Arjan van de Ven <arjan@linux.intel.com>]

Bjorn Helgaas wrote:
> 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?

not unless the device is enabled.


> How do vbetool and X coordinate their usage of "enable"?

Just never disable :)