The serirq routing table is split over two registers, the calculation
for the high irqs in the second register did not subtract the irq
offset. This was spotted by Coverity as a shift-by-negative. Fix this
and change the open-coded shifting and masking to use extract32()
function so it's less error-prone.

This went unnoticed because irqs >= 14 are not used in a standard
QEMU/OPAL boot, changing the first QEMU serial-isa irq to 14 to test
does demonstrate serial irqs aren't received, and that this change
fixes that.

Cc: qemu-stable@nongnu.org
Reported-by: Cédric Le Goater <clg@redhat.com>
Resolves: Coverity CID 1558829 (partially)
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 hw/ppc/pnv_lpc.c | 10 ++++++++--
 target/ppc/cpu.h |  1 +
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/hw/ppc/pnv_lpc.c b/hw/ppc/pnv_lpc.c
index f8aad955b5..80b79dfbbc 100644
--- a/hw/ppc/pnv_lpc.c
+++ b/hw/ppc/pnv_lpc.c
@@ -435,13 +435,19 @@ static void pnv_lpc_eval_serirq_routes(PnvLpcController *lpc)
         return;
     }
 
+    /*
+     * Each of the ISA irqs is routed to one of the 4 SERIRQ irqs with 2
+     * bits, split across 2 OPB registers.
+     */
     for (irq = 0; irq <= 13; irq++) {
-        int serirq = (lpc->opb_irq_route1 >> (31 - 5 - (irq * 2))) & 0x3;
+        int serirq = extract32(lpc->opb_irq_route1,
+                                    PPC_BIT32_NR(5 + irq * 2), 2);
         lpc->irq_to_serirq_route[irq] = serirq;
     }
 
     for (irq = 14; irq < ISA_NUM_IRQS; irq++) {
-        int serirq = (lpc->opb_irq_route0 >> (31 - 9 - (irq * 2))) & 0x3;
+        int serirq = extract32(lpc->opb_irq_route0,
+                               PPC_BIT32_NR(9 + (irq - 14) * 2), 2);
         lpc->irq_to_serirq_route[irq] = serirq;
     }
 }
diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index 321ed2da75..bd32a1a5f8 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -40,6 +40,7 @@
 
 #define PPC_BIT_NR(bit)         (63 - (bit))
 #define PPC_BIT(bit)            (0x8000000000000000ULL >> (bit))
+#define PPC_BIT32_NR(bit)       (31 - (bit))
 #define PPC_BIT32(bit)          (0x80000000 >> (bit))
 #define PPC_BIT8(bit)           (0x80 >> (bit))
 #define PPC_BITMASK(bs, be)     ((PPC_BIT(bs) - PPC_BIT(be)) | PPC_BIT(bs))
-- 
2.45.2