On 29/03/16 16:24, Arnd Bergmann wrote: > On Tuesday 29 March 2016 08:10:08 Tim Harvey wrote: >> Arnd, >> >> Right, on the IMX the MSI interrupt is GIC-120 which is also the >> legacy INTD and I do see that if I happen to put a radio in a slot >> where due to swizzling its pin1 becomes INTD (GIC-120) the interrupt >> does fire and the device works. Any other slot using GIC-123 (INTA), >> GIC-122 (INTB), or GIC-121 (INTC) never fires so its very possible >> that something in the designware core is masking out the legacy irqs. > > Interesting. I was actually expecting the opposite here, having the > IRQs only work if they are not IntD. > > >> I typically advise our users to 'not' enable MSI because >> architecturally you can spread 4 distinct legacy irq's across CPU's >> better than a single shared irq. > > That is a very good point, I never understood why we want to enable > MSI support on any PCI host bridge that just forwards all MSIs > to a single IRQ line. Originally MSI was meant as a performance > feature, but there is nothing in this setup that makes things go > faster, and several things that make it go slower. Feature-ticking exercise. "We support MSI", never mind if that negating the benefits of the mechanism and ending up with disastrous impacts on interrupt affinity, and a set of open questions regarding the effect of the MSI as a DMA fence. /me stops ranting for the day... M. -- Jazz is not dead. It just smells funny... -- 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
