3 Jun
2014
3 Jun
'14
1:53 a.m.
Sorry but I'm not sure I can follow what you mean. Why setting BUS_MASTER in PCI config would fail on real hardware?
Enabling bus mastering on a PCI device allows the device to generate reads and writes on the PCI bus.
It fails in exciting and mysterious ways if you haven't yet set up bus mastering on your PCI-PCI bridges and your PHB yet. And related config, e.g. the windows on those bridges.
Things get a lot more interesting if you have an IOMMU, too. DMA is evil. Scared yet? You should be.
Segher