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SubjectRe: Add a "enable" sysfs attribute to the pci devices to allow userspace (Xorg) to enable devices without doing foul direct access
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On May 6, 2006, at 19:16:25, Krzysztof Halasa wrote:
> "Jon Smirl" <jonsmirl@gmail.com> writes:
>>> The card in question _has_ a driver. I, for example, just need a
>>> way to write EEPROM data to it (vendor/device ID etc). The card
>>> has to be selected by PCI bus and slot (device) number, not by
>>> device class and/or IDs, because it can contain garbage and/or
>>> some generic IDs with generic device class.
>>
>> Hardware like you describe violates the PCI spec
>
> What exactly does it violate?

"device class and/or IDs ... can contain garbage". That seems to
violate PCI spec to me.

>> I would probably handle this by writing an unbound device driver
>> that exposes a sysfs file for bus:slot. When you write the
>> bus:slot to the file it would then bind to the appropriate
>> hardware and enable it. The newly bound driver would support the
>> driver firmware loader interface as a means of getting your data in.
>
> What is also needed is that end users perform this task from time
> to time. They generally don't want to have to compile the kernel :-)
>
> You know, even now it can be done (entirely in userspace), and only
> enabling the device seems a bit dangerous.

Jon Smirl gave a great description of exactly how to write such a
"driver". I seem to recall that we already have the ability to
trigger manual PCI binding by bus:slot number; in combination with an
appropriate "write EEPROM with firmware file" driver that has no
default list of PCI devices; you could easily manually trigger a bind
of the device. On the other hand I would personally never put such a
device in my system, what if the garbage device IDs happened to match
a device with poorly-written PCI IDE drivers that panic when they
bind to a device which does not match their expectations? In any
case what you really need for all those cases is a simplistic stub
driver that provides some sort of in-kernel mutual exclusion.

Cheers,
Kyle Moffett

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