Re: [Qemu-devel] [Qemu-ppc] [PATCH: RFC] Adding BAR0 for e500 PCI controller

[Scott Wood]

On 08/14/2012 07:50 AM, Bharat Bhushan wrote:
> PCI Root complex have TYPE-1 configuration header while PCI endpoint
> have type-0 configuration header. The type-1 configuration header have
> a BAR (BAR0). In Freescale PCI controller BAR0 is used for mapping pci
> address space to CCSR address space. This can used for 2 purposes: 1)
> for MSI interrupt generation 2) Allow CCSR registers access when configured
> as PCI endpoint, which I am not sure is a use case with QEMU-KVM guest.
> 
> What I observed is that when guest read the size of BAR0 of host controller
> configuration header (TYPE1 header) then it always reads it as 0. When
> looking into the QEMU hw/ppce500_pci.c, I do not find the PCI controller
> device registering BAR0. I do not find any other controller also doing so
> may they do not use BAR0.
> 
> There are two issues when BAR0 is not there (which I can think of):
> 1) There should be BAR0 emulated for PCI Root comaplex (TYPE1 header) and
> when reading the size of BAR0, it should give size as per real h/w.
> 
> 2) Do we need this BAR0 inbound address translation?
>       When BAR0 is of non-zero size then it will be configured for PCI
> address space to local address(CCSR) space translation on inbound access.
> The primary use case is for MSI interrupt generation. The device is
> configured with a address offsets in PCI address space, which will be
> translated to MSI interrupt generation MPIC registers. Currently I do
> not understand the MSI interrupt generation mechanism in QEMU and also
> IIRC we do not use QEMU MSI interrupt mechanism on e500 guest machines.
> But this BAR0 will be used when using MSI on e500.

This patch is only trying to address #1, right?  I don't see any
connection from this BAR to CCSR.

> +    memory_region_init_io(&h->bar0, &pci_host_conf_be_ops, h,
> +                          "PCIHOST-bar0", 0x1000000);

0x01000000 is correct for e500mc-based systems, but it should be
0x00100000 for e500v2-based systems.

-Scott