Message-ID: <445A5AE1.5000904@linux.intel.com>
Date: Thu, 04 May 2006 21:49:53 +0200
From: Arjan van de Ven <arjan@linux.intel.com>
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To: Bjorn Helgaas <bjorn.helgaas@hp.com>
CC: linux-pci@atrey.karlin.mff.cuni.cz, Dave Airlie <airlied@linux.ie>,
       Andrew Morton <akpm@osdl.org>, greg@kroah.com,
       linux-kernel@vger.kernel.org, pjones@redhat.com
Subject: Re: Add a "enable" sysfs attribute to the pci devices to allow userspace
 (Xorg) to enable devices without doing foul direct access
References: <1146300385.3125.3.camel@laptopd505.fenrus.org> <200605041309.53910.bjorn.helgaas@hp.com> <445A51F1.9040500@linux.intel.com> <200605041326.36518.bjorn.helgaas@hp.com>
In-Reply-To: <200605041326.36518.bjorn.helgaas@hp.com>
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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 :)


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