[Qemu-devel] [RFC] Proposal: PCI/PCIe: inbound BAR0 emulation for PCI controller (Root Complex)

[Bhushan Bharat-R65777]

Hi All,

When Freescale PCI controller configured in Root Complex mode then, its 
configuration header (type 1) have one inbound BAR (BAR0, called as CCSRBAR). 
And rest of BARs (inbound and outbound) are supported by ATMU registers, which 
are outside the Type 1 configuration header. This BAR0 of Type 1 configuration 
header always translate to CCSR space and is of the size of CCSR. This BAR0 
(inbound window) is required for MSI interrupts support. With this window, the 
pci devices can write to the MPIC MSI registers to generate MSI interrupt.

As far as I know, as of now no emulated PCI controller supports this BAR0 in 
type 1 configuration header. But probably (I think so) that supporting this is 
not of big concern, but the point is that this window (BAR0) translate to 
mmio-regs (CCSR) and not to DDR memory.

So I have couple of concerns here:

1. Whenever PCI device does need DMA then these windows (inbound and outbound 
ATMUs registers) need to used to translate pci address to system physical 
address (Sometime we also call this as cpu address space). This will probably 
be done by : [Qemu-devel] [PATCH 00/12] IOMMU Infrastructure : patch-set ( I am 
trying to understand these patches :-))

2. Hook up this inbound BAR0 in the above patch-set to translate to mmio-regs. 
As this would be controller specific, a callback will be registered for 
translation. Now it will be upto the controller specific code on how it 
translates. As this is needed only for MSI interrupt, maybe, initially we do 
not do anything initially, till we want MSI emulation in QEMU.

Please provide your comment.

Thanks
-Bharat