The POWER8 LPC ISA device irqs all get combined and reported to the line
connected the PSI LPCHC irq. POWER9 changed this so only internal LPC
host controller irqs use that line, and the device irqs get routed to
4 new lines connected to PSI SERIRQ0-3.
POWER9 also introduced a new feature that automatically clears the irq
status in the LPC host controller when EOI'ed, so software does not have
to.
The powernv OPAL (skiboot) firmware managed to work because the LPCHC
irq handler scanned all LPC irqs and handled those including clearing
status even on POWER9 systems. So LPC irqs worked despite OPAL thinking
it was running in POWER9 mode. After this change, UART interrupts show
up on serirq1 which is where OPAL routes them to:
cat /proc/interrupts
...
20: 0 XIVE-IRQ 1048563 Level opal-psi#0:lpchc
...
25: 34 XIVE-IRQ 1048568 Level opal-psi#0:lpc_serirq_mux1
Whereas they previously turn up on lpchc.
Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
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