MIPS: PowerTV: Fix support for timer interrupts with > 64 external IRQs

The MIPS processor is limited to 64 external interrupt sources. Using a
greater number without IRQ sharing requires reading platform-specific
registers. On such platforms, reading the IntCtl register to determine
which interrupt corresponds to a timer interrupt will not work.

On MIPSR2 systems there is a solution - the TI bit in the Cause register,
specifically indicates that a timer interrupt has occured. This patch uses
that bit to detect interrupts for MIPSR2 processors, which may be expected
to work regardless of how the timer interrupt may be routed in the hardware.

Signed-off-by: David VomLehn (dvomlehn@cisco.com)
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/804/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/cevt-r4k.c

@@ -97,7 +97,7 @@ void mips_event_handler(struct clock_event_device *dev)
  */
 static int c0_compare_int_pending(void)
 {
-	return (read_c0_cause() >> cp0_compare_irq) & 0x100;
+	return (read_c0_cause() >> cp0_compare_irq_shift) & (1ul << CAUSEB_IP);
 }
 
 /*

arch/mips/kernel/traps.c

@@ -1403,6 +1403,7 @@ extern void flush_tlb_handlers(void);
  * Timer interrupt
  */
 int cp0_compare_irq;
+int cp0_compare_irq_shift;
 
 /*
  * Performance counter IRQ or -1 if shared with timer
@@ -1493,8 +1494,9 @@ void __cpuinit per_cpu_trap_init(void)
 	 *  o read IntCtl.IPPCI to determine the performance counter interrupt
 	 */
 	if (cpu_has_mips_r2) {
-		cp0_compare_irq = (read_c0_intctl() >> 29) & 7;
-		cp0_perfcount_irq = (read_c0_intctl() >> 26) & 7;
+		cp0_compare_irq_shift = CAUSEB_TI - CAUSEB_IP;
+		cp0_compare_irq = (read_c0_intctl() >> INTCTLB_IPTI) & 7;
+		cp0_perfcount_irq = (read_c0_intctl() >> INTCTLB_IPPCI) & 7;
 		if (cp0_perfcount_irq == cp0_compare_irq)
 			cp0_perfcount_irq = -1;
 	} else {