The PCI spec says that the interrupt mask in the MSI-X capability takes up the bottom bit of the 32-bit Vector Control word and the other 31 bits are reserved. The PCIe 2.1 spec defines 16 of those bits to be used for the Steering Tag table (related to the TPH capability). As far as I can tell, changing the Steering Tag is a rare occurrence. The spec notes that devices should be quiesced (or merely have TPH disabled) while the Steerring Tags are being programmed. I would like it to be a rule that MSI-X must be disabled while Steering Tags are reprogrammed, then re-enabled afterwards. That way, we can cache the value of the interrupt mask bit, and avoid an MMIO read when masking interrupts. The specs are very clear that the entire word must be written at once; we can't just write the lowest byte. Thoughts on this are greatly appreciated, especially from anyone who has insight into how TPH and ST are going to be used by device drivers. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- 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
