On 16/10/14 10:33, Daniel Thompson wrote: >> The blocker on this work right now is the annoying Versatile Express >> platform, which pretty much means that we currently can't push the >> code into the GIC to support FIQs. As long as adding FIQ support to >> the GIC results in the Versatile Express becoming non-bootable, the >> idea of using FIQs is a total non-starter. >> >> Or we decide that we dump the platform completely (which will upset >> a number of developers.) >> >> I have patches I'm using for trigger_all_cpu_backtrace() which I'm >> maintaining privately in my tree until we can get the FIQ situation >> sorted. > > I do hope to gain (remote) access to a vexpress at some point just to > pick at this issue a little.
This week with the help of one of my colleagues (thanks Tixy) I have been able to run some tests and figure out what it going on on vexpress-a9. The summary is that on some GICv1 implementations the bit to enable group 1 interrupts cannot be accessed using secure memory accesses. More specifically the presence/absence of the EnableGrp1 bit in the secure version GICD_CTRL register is implementation defined. My original patches overlooked this and as a result the existing code will migrate all interrupts to group but then cannot enable delivery of group 1 interrupts. I'm planning to respin the code so it will automatically disable FIQ support when the EnableGrp1 bit is not implemented. This means vexpress-a9 will not benefit from FIQ support but will also not be harmed by it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
