microblaze/petalogix_s3adsp1800_mmu: Fix UART IRQ

The UART IRQ is edge sensitive, whereas the machine was registering it
as level sensitive. Fix.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
intc/xilinx_intc: Don't clear level sens. IRQs without ACK

For level sensitive interrupts, ISR bits are cleared when the input pin
is lowered. This is incorrect. Only software can clear ISR bits (via
IAR or direct write to ISR with !MER(2)).

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
intc/xilinx_intc: Handle level interrupt retriggering

Acking a level sensitive interrupt should have no effect if the
interrupt pin is still asserted. The current implementation requires
and edge condition to occur for setting a level sensitive IRQ, which
means an ACK can clear a level sensitive interrupt, until the original
source strobes the interrupt again.

Fix by keeping track of the interrupt pin state and setting ISR based
on this every time update_irq() is called.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
intc/xilinx_intc: Inhibit write to ISR when HIE

When the Hardware Interrupt Enable (HIE) bit is set, software cannot
change ISR. Add write guard accordingly.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
intc/xilinx_intc: Dont lower IRQ when HIE cleared

This is a little strange. It is lowering the parent IRQ pin on input
when HIE is cleared. There is no such behaviour in the real hardware.

ISR changes based on interrupt pin state are already guarded on HIE
being set. So we can just delete this if in its entirety.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>