Re: PCI Express

[Grant Grundler <iod00d@hp.com>]

On Wed, Mar 09, 2005 at 08:35:00AM -0800, Nguyen, Tom L wrote:
> Existing MSI support implements a direct
> memory-write mechanism (generic solution without platform dependency and
> limitation to MSI-X support as an example). With existing direct
> memory-write mechanism, a device's MSI address is configured with
> current running CPU as a target.

At some point, PARISC (and Alpha?) will also want to support MSI
using "direct memory write". But like Altix, does not implement
0xfeeXXXXX (1) PIB since PARISC arch predates PCI by a decade or so.

We'll have to figure out which platform specific hooks would enable
parisc/alpha/altix to use existing PCI MSI/MSI-X support.

PA-RISC IPI is as straight forward as Jesse described - just write
to a per CPU address with a data value (vector).

thanks,
grant

(1) the most recent two or three PA-RISC chipsets do implement 0xfeeXXXXX
interrupt block. But firmware hands us the CPU "ID/EID" values to use
when programming the IO SAPIC IRT. See drivers/parisc/iosapic.c
iosapic_set_irt_data() for more details.

Bottomline is, even if we know it's implemented in HW, we don't know if
we are using 0xfeeXXXXX or not for IO SAPIC today. platform hooks
into MSI code would have to sort that out.