Re: [PATCH 7/7] powerpc: Added PCI MSI support using the HSTA module

Alistair Popple
2014-02-25T05:54:58Z

On Sat, 22 Feb 2014 07:41:26 Benjamin Herrenschmidt wrote:
> On Fri, 2014-02-21 at 15:33 +0100, Arnd Bergmann wrote:

[...]

>
> Should we (provided it's possible in HW) create two ranges instead ? One
> covering RAM and one covering MSIs ? To avoid stray DMAs whacking random
> HW registers in the chip ...
>

The thought occurred to me but I figured if we had stray DMAs then they could
already whack random bits of system memory which would likely break your
system anyway so I wasn't sure how much we'd gain. I guess whacking random HW
registers is arguably a bit worse though.

I did a bit of digging into the HW documentation and it looks like it _may_ be
possible to create a second range that would limit access to a subset of HW
registers, although there doesn't seem to be much flexibility. Personally I'm
not sure it justifies the work, but I'm happy to look into it a bit more if
you feel it's important?

- Alistair

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