On 16/10/14 10:33, Daniel Thompson wrote:

quoted

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.