> W dniu 6 kwietnia 2011 23:08 uÅytkownik Michael BÃsch <mb@xxxxxxxxx> napisaÅ: > > On Wed, 2011-04-06 at 23:01 +0200, RafaÅ MiÅecki wrote: > >> W dniu 6 kwietnia 2011 22:57 uÅytkownik Michael BÃsch <mb@xxxxxxxxx> napisaÅ: > >> > On Wed, 2011-04-06 at 22:42 +0200, RafaÅ MiÅecki wrote: > >> >> 2011/4/6 RafaÅ MiÅecki <zajec5@xxxxxxxxx>: > >> >> > If we want to have two drivers working on two (different) cores > >> >> > simultaneously, we will have to add trivial mutex to group core > >> >> > switching with core operation (read/write). > >> >> > >> >> With a little of work we could avoid switching and mutexes on no-host > >> >> boards. MMIO is not limited to one core at once in such a case. > >> > > >> > I don't think that this is a problem at all. > >> > All that magic does happen inside of the bus I/O handlers. > >> > Just like SSB does it. > >> > From a driver point of view, the I/O functions just need to > >> > be atomic. > >> > > >> > For SSB it's not always 100% atomic, but we're always safe > >> > due to some assumptions being made. But this is an SSB implementation > >> > detail that is different from AXI. So don't look too closely > >> > at the SSB implementation of the I/O functions. You certainly want > >> > to implement them slightly differently in AXI. SSB currently doesn't > >> > make use of the additional sliding windows, because they are not > >> > available in the majority of SSB devices. > >> > > >> > The AXI bus subsystem will manage the sliding windows and the driver > >> > doesn't know about the details. > >> > >> Sure, I've meant mutex inside bcmai (or whatever name), not on the driver side! > >> > >> In BCMAI: > >> bcmai_read() { > >> mutex_get(); > >> switch_core(); > >> ioread(); > >> mutex_release(); > >> } > > > > Yeah that basically is the idea. But it's a little bit harder than that. > > The problem is that the mutex cannot be taken in interrupt context. > > A spinlock probably is a bit hairy, too, depending on how heavy > > a core switch is on AXI. > > > > On SSB we workaround this with some (dirty but working) assumptions. > > > > On AXI you probably can do lockless I/O, if you use the two windows > > (how many windows are there?) in a clever way to avoid core switching > > completely after the system was initialized. > > We have 2 windows. I didn't try this, but let's assume they have no > limitations. We can use first window for one driver only, second > driver for second driver only. That gives us 2 drivers simultaneously > working drivers. No driver need to reset core really often (and not > inside interrupt context) so we will switch driver's window to agent > (from core) only at init/reset. > > The question is what amount of driver we will need to support at the same time. > I guess (correct me please, Broadcom guys if I'm wrong) there are two functions two-head w11 pci host and therefore 4 sliding windows, 2 per each function. You really was in need for core switching for PCI SSB hosts, but seem all that stuff for PCI switching in current bcm80211/utils code is rudimentary stuff left from PCI times when you was required to use sliding window for chipcommon and pci bridge core access. Have nice day, George -- 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