Dear Jason Gunthorpe, On Wed, 6 Feb 2013 10:50:19 -0700, Jason Gunthorpe wrote: > No.. PCI end devices are required to decode all 32 bits of address, > less the bits requires for their allocation. So a device with 64 bytes > of IO will match bits 31:6 and then use bits 5:0 for the internal > register. > > So a full 32 bit address is technically fine, according to the spec, > however: > - The 32 bit decode is an optional feature on bridges > - Some devices are broken because x86 only uses the low 64k. Thanks again for the great explanation, it is now clear to me. > So for best compatibility it is ideal to put everything in the low > 64k. > > However, IO space really should not be used by anything except very > legacy devices, so if the MMU business is a hassle for some reason I'd > just go with the 64k aligned method. Me too :-) It's what is done on Kirkwood since a long time, and apparently hasn't caused any trouble so far. > > Why would you need to adjust the length? If Linux allocates a 2 MB > > resource on a 1 MB boundary, we simply increase the start address to > > the next 2 MB boundary, and that's it. Why would the length need to > > change? > > Well, lets say 3MB is the example. A 3mb region needs to fit inside a > 4mb MBUS window. If you align the start to 4mb then the pci-e core > needs to know that it can't use the extra 1mb covered by the mbus > window. mbus windows must not overlap. Grumble, grumble, you're right. I now understand. Need to think of it, because the current pcibios_window_alignment() thing only allows to adjust the start address if I'm correct. But I'll have a more detailed look. Or maybe Russell can comment on this specific topic? Thanks! Thomas -- Thomas Petazzoni, Free Electrons Kernel, drivers, real-time and embedded Linux development, consulting, training and support. http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
