Re: [Qemu-devel] PCIe Transaction handling in Qemu

[Paul Brook]

> I have some questions about PCIe operations sssuming the device has MMIO
> handlers involved (as shown above).

> 1. Will all PCIe config operations
> ALWAYS use the installed config handlers? Or can PCIe config operations
> use the MMIO handlers? 

Access to PCI config space is provided by the PCI host bridge. It has nothing 
to do with any memory BARs the device may have.  The host bridge may expose 
this in any way it chooses, including but not limited to ISA IO ports or a 
memory mapped region of its own.  Ether way the device doesn't care.

> 2. Assuming that both PCI config and MMIO
> operations can use the MMIO handlers, is there any way I can identify if a
> transaction is a config or a memory transaction?

Incorrect assumption. Memory and Config accesses ae completely separate.

> 3.a. What address is
> passed on the MMIO handlers for config and MMIO operations? From
> pci_data_write in pci_host.c, it appears that config operations send only
> the offset into the config region. I couldn't determine what address is
> passed for MMIO operations. b. Is it an offset from the BAR for MMIO
> operations?

Th offset from the start of the region.

>    c. How do I get the full physical address?

You don't.  "Full physical address" is a fairly ill defined term. Physical 
addresses are local to a particular bus. It's common for CPU/ram and each PCI 
bus to have completely independent physical address spaces, with the host 
bridge providing mapping between the two.

>    d. What address does a PCIe device expect to see - physical or offset
> for? 

Offset. Old versions of qemu used to pass the cpu physical address. This was a 
bug.

> e. Is there anyway I can find out what the bus and device numbers are
> once inside the config and MMIO handlers? i.e once the execution has
> reached the pci_cirrus_write_config() or cirrus_vga_mem_readb(..) from the
> code above?

No. The device does not, and should not know this. 

Paul