[Qemu-devel] Re: Re: PCI address question

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 29, 2009 at 12:30:02PM +0100, Màrius Montón wrote:
> Lennart Sorensen wrote:
> 
>     On Tue, Oct 27, 2009 at 04:05:25PM +0100, Màrius Montón wrote:
> 
> 
>         Màrius Montón wrote:
> 
> 
>             Hello,
> 
>             For my PCI device to QEMU, I need the real address the PCI bus is using
>             to access my device. For a IO BAR (PCI_ADDRESS_SPACE_IO), I receive the
>             real address (like 0xc200 or similar), but when registering a
>             PCI_ADDRESS_SPACE_MEM I only receive the offset to the BAR.
> 
>             How I can receive or obtaint the real address on each access to my device?
> 
>             Cjeers,
> 
>             Màrius
> 
> 
> 
>         nobody can tell me anything? :(
> 
> 
>     Add the offset to the address in the bar?
> 
> The problem is how to know what bar is accessing in case I have only one
> function for all BARs.

I expect that's unusual: different BARs usually have different
functionality. Just implement different functions and pass
calls on to a shared helper?

>     After all the OS is allowed to change your BAR if it wants to.
>     So internally the only thing that makes sense to a PCI device is the
>     offset from it's base address.
> 
>     You listen to addresses at your IO range, and at your memory BAR range.
>     What you do when you see a request for your range then depends on the
>     offset that address had from the current base.  This would also be true
>     for the IO.
> 
> I know all PCI internals, but I don't understand why for IO I receive all
> address and only the offset for MEM BARs (or I'm wrong?)
> 
> Màrius

PCI only calls a map method. I think this gets a 32 bit address, not BAR offset:

               r->addr = new_addr;
               if (r->addr != -1) {
                   r->map_func(d, i, r->addr, r->size, r->type);
               }


-- 
MST