On 12/22/2007 11:52 PM, Jeff Garzik wrote: > > Absolutely. > > But regardless of problems, enabling should be done globally, not per > device...
The "enabling globally" requirement, i.e. not per-device, neither depending on reg >= 256 seems a very debatable assumption (IMHO a big mistake) that seems to be responsible for many of the problems seen in the past. There might be for a very long time AMD-architectures where extended-conf-space access for pci-express device works and is beneficial (and where mmconf is not supported by the hardware on non-pci-express devices). You are basically saying you don't want ever to support extended-conf-space globally for those systems, where it would be so easy to precisely use mmconf *only* when attempting *extended-conf-space * (>= 256) to some device (that provides a strong guarantee that you will never break anything unless somebody actually tries to use the extended-conf-space). Supporting extended-conf-space is independant of the issue of using mmconf for legacy conf-space. There is no real reason to use the same method to access both. I have seen several arguments used that were implying that, and they all seem really bogus to me. Not only are the two ranges (<= 256 and >= 256) structurally independant (you have totally independant capabilities lists that are independantly organized in each of them), even if they were not there is no consistency issue that cannot be dealt with a memory barrier, and the concern about taking an extra branch for each pci-conf-space access is also bogus once you look at the numbers. By possibly using different implementations for the two ranges you avoid introducing a new API, you avoid taking risks with mmconf when you don't need it. That doesn't preclude using mmconf for everything either if the user requests it or based on enough knowledge of the system to be sure nothing will break. Loic -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
