[POWERPC] mpic: Fix use of uninitialized variable

Compiling ppc64_defconfig with gcc 4.3 gives thes warnings:

arch/powerpc/sysdev/mpic.c: In function 'mpic_irq_get_priority':
arch/powerpc/sysdev/mpic.c:1351: warning: 'is_ipi' may be used uninitialized in this function
arch/powerpc/sysdev/mpic.c: In function 'mpic_irq_set_priority':
arch/powerpc/sysdev/mpic.c:1328: warning: 'is_ipi' may be used uninitialized in this function

It turns out that in the cases where is_ipi is uninitialized, another
variable (mpic) will be NULL and it is dereferenced.  Protect against
this by returning if mpic is NULL in mpic_irq_set_priority, and removing
mpic_irq_get_priority completely as it has no in tree callers.

This has the nice side effect of making the warning go away.
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/sysdev/mpic.c

@@ -1331,6 +1331,9 @@ void mpic_irq_set_priority(unsigned int irq, unsigned int pri)
 	unsigned long flags;
 	u32 reg;
 
+	if (!mpic)
+		return;
+
 	spin_lock_irqsave(&mpic_lock, flags);
 	if (is_ipi) {
 		reg = mpic_ipi_read(src - mpic->ipi_vecs[0]) &
@@ -1346,23 +1349,6 @@ void mpic_irq_set_priority(unsigned int irq, unsigned int pri)
 	spin_unlock_irqrestore(&mpic_lock, flags);
 }
 
-unsigned int mpic_irq_get_priority(unsigned int irq)
-{
-	unsigned int is_ipi;
-	struct mpic *mpic = mpic_find(irq, &is_ipi);
-	unsigned int src = mpic_irq_to_hw(irq);
-	unsigned long flags;
-	u32 reg;
-
-	spin_lock_irqsave(&mpic_lock, flags);
-	if (is_ipi)
-		reg = mpic_ipi_read(src = mpic->ipi_vecs[0]);
-	else
-		reg = mpic_irq_read(src, MPIC_INFO(IRQ_VECTOR_PRI));
-	spin_unlock_irqrestore(&mpic_lock, flags);
-	return (reg & MPIC_VECPRI_PRIORITY_MASK) >> MPIC_VECPRI_PRIORITY_SHIFT;
-}
-
 void mpic_setup_this_cpu(void)
 {
 #ifdef CONFIG_SMP

include/asm-powerpc/mpic.h

@@ -428,12 +428,11 @@ extern void mpic_init(struct mpic *mpic);
  */
 
 
-/* Change/Read the priority of an interrupt. Default is 8 for irqs and
+/* Change the priority of an interrupt. Default is 8 for irqs and
  * 10 for IPIs. You can call this on both IPIs and IRQ numbers, but the
  * IPI number is then the offset'ed (linux irq number mapped to the IPI)
  */
 extern void mpic_irq_set_priority(unsigned int irq, unsigned int pri);
-extern unsigned int mpic_irq_get_priority(unsigned int irq);
 
 /* Setup a non-boot CPU */
 extern void mpic_setup_this_cpu(void);