Re: MI overrides of bus_dma(9), bus_space(9), pci(9)

[David Young <dyoung%pobox.com@localhost>]

On Thu, Mar 11, 2010 at 12:58:30PM -0800, Matt Thomas wrote:
> 
> On Mar 11, 2010, at 12:31 PM, David Young wrote:
> 
> > On Thu, Mar 11, 2010 at 12:20:41PM -0800, Matt Thomas wrote:
> >> On Mar 11, 2010, at 11:40 AM, David Young wrote:
> >>> Resource management:
> >>> 
> >>>   PCI-* bridges can override bus_space_alloc(9)/bus_space_free(9)
> >>>       in order to (1) allocate space from the upstream bus, (2)
> >>>       widen/narrow its I/O- or memory-space window.  Then we can
> >>>       provide a reliable rbus-like facility to detachable buses
> >>>       through bus_space(9).
> >> 
> >> bus_dma_subregion can be used for that.  So bus_space_subregion.
> > 
> > Matt,
> > 
> > How do we open the windows?
> 
> I don't see a reason to do that but you could allocate new larger 
> subregions from the parent.

Let's say that we have this PCI setup:

Host-PCI bridge: forwards MMIO 0xff000000-0xffffffff to PCI bus
    |
   pci0
    |
    +-------- - - -
    |
PCI-PCI bridge: forwards MMIO in [0xffff0000-0xffffffff] to secondary
    |
   pci1
    |
    +------------------------+-----------------------+
    |                        |                       |
    PCI-CardBus bridge       IDE controller          video adapter
    |
    +--------+
    |        |
   cardbus0 cardbus1
    |        |
    |        |
    |        |
    NIC      NIC

The BIOS has exclusively assigned MMIO regions to each PCI adapter.  It
may or may not have assigned a range to the CardBus bridge itself.  It
has probably not reserved space for the CardBus NICs, especially not if
they were attached after boot-up.

We have to exclusively assign MMIO space to each CardBus NIC's
registers.  If the PCI-PCI bridge does not forward an address range that
is big enough to fit the NICs' registers, then we have to reprogram the
bridge to forward a wider range.

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 278-3933