On Monday 01 March 2010 01:22:50 Michael Buesch wrote: > Well, you are confusing address spaces here. > > On a PCI based SSB device all host-side MMIO transfers go into > the PCI device's address space first. The core-switching moves the window of > the SSB address space that is mapped into 0-0xFFF of the PCI address space. > So if you write to anything above 0xFFF on the PCI device, the write will > not (directly) map to the SSB bus or any device on it. > On the PCI device there is more stuff mapped on top of the SSB sliding > window. For example the SPROM is mapped right on top of it. > > So it might be the case that on a PCI-E device the PCI-E-core's registers > are permanently mapped into 0x2000 of the PCI address apace. This is to > avoid sliding the SSB address space window when accessing the PCI-E core. > This can have several reasons: For one speed (unlikely) and for another > to avoid concurrency and ugly races when we need to access the PCI-E core > while the wireless core is already running and generating interrupts. > Note that this is a GUESS, but it would make sense to me. > It would be cool if somebody could compare more registers of the PCI-E > core using the sliding window and the 0x2000 + reg method to check my theory. > So what's the status on this? I think the fact that the testing patch showed some improvement is a clear indicator that something in the PCI-E core init is wrong. It's also not surprising that something is going wrong there. The whole PCI-E core code basically is undebugged. I wrote most of it long time ago, but I still don't have a device that tests it (and probably won't get one anytime soon). So I'm really not surprised that there are bugs. There also are missing parts. A bug in the PCI-E core code is able to show such behavior, because all memory transfers (MMIO and DMA) from the PCI device to the wireless core are translated by the PCI-E core. I think the whole PCI-E core code has to be audited (also the specs, probably). -- Greetings, Michael. -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
