[libvirt] [RFC PATCH] support multifunction PCI device

[Paolo Bonzini]

On 05/11/2011 09:55 AM, Daniel P. Berrange wrote:
> Hmm, that's kinda wierd&  i'm suprised it works, particularly for LSI
> since I thought guest drivers would need support for multifunction too.

For well-behaved {kernel,device,driver}s multifunction should be totally 
transparent.

Example from 
http://msdn.microsoft.com/en-us/library/ff542756%28v=vs.85%29.aspx

"Since the system-supplied bus driver handles the multifunction 
semantics, the function drivers can be the same drivers that would be 
used if the functions were packaged as individual devices.  Rather than 
enumerating one multifunction device, the PCI driver enumerates two 
child devices. The PnP manager treats each child device like a typical 
device. [...] The PCI driver arbitrates the resources for the child 
devices and manages any other multifunction aspects of the device.

And an old whitepaper also from MS at 
http://msdn.microsoft.com/en-us/windows/hardware/gg463194

"Each functional unit must be able to operate as a separate device, even 
if it happens to be serviced by an instance of the same driver(s) as 
another functional unit on the device. The operating system must be able 
to separately access each logical device that is individually 
enumerated, configure the device resources independently, and disable 
individual devices. [...]

Each separate functional unit on a multifunction device must not share 
addresses or registers with other functional units [...]

No start-order dependencies. The operating system must be able to 
configure and manage functions in any order. Therefore, no function on a 
multifunction device can depend on another device (that is, another 
function) to be started before the function can be started by the 
operating system. [...]

No hidden dependencies. Separate functional units must be able to 
operate concurrently, without interfering with each other or with other 
devices on the system. [...]

Vendors of multifunction devices should implement a separate 
configuration space with a unique device ID and independent resources 
for each function. [....]"

Paolo