RE: Question on using MSI in PCI driver

[Nguyen, Tom L]

On Monday, June 21, 2004 Roland Dreier wrote:

> The problem is that if I follow the standard route in my driver and
> call pci_request_regions() during init (since I want to claim my whole
> device), the request_mem_region in msix_capability_init will fail.
> Now, for my device, the MSI-X table happens to fall in the middle of a
> BAR, and I need to access stuff on both sides of it in that BAR.  To
> make things even worse for me, my device has two more BARs I want to
claim.
>
> So it seems I am forced to turn my nice clean pci_request_regions()
> call into two calls to request_mem_region() (to get the beginning and
> end of the BAR with the MSI-X table in it) and two more calls to
> pci_request_region() (to get the other two BARs).
>

The PCI 3.0 specification has implementation notes that MMIO address
space for a device's MSI-X structure should be isolated so that the 
software system can set different page for controlling accesses to 
the MSI-X structure. The implementation of MSI patch requires the PCI
subsystem, not a device driver, to maintain full control of the MSI-X
table/MSI-X PBA and MMIO address space of the MSI-X table/MSI-X PBA. 
A device driver is prohibited from requesting the MMIO address space 
of the MSI-X table/MSI-X PBA. Otherwise, the PCI subsystem will fail 
enabling MSI-X on its hardware device when it calls the function 
pci_enable_msi(). 

Thanks,
Long
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