sparc64: Add some more commentary to __raw_local_irq_save()

Suggested by Peter Zijlstra

Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/sparc/include/asm/irqflags_64.h b/arch/sparc/include/asm/irqflags_64.h
index a16e94c..bfa1ea4 100644 (file)
--- a/arch/sparc/include/asm/irqflags_64.h
+++ b/arch/sparc/include/asm/irqflags_64.h
@@ -80,6 +80,13 @@ static inline unsigned long __raw_local_irq_save(void)
 
        /* Disable interrupts to PIL_NORMAL_MAX unless we already
         * are using PIL_NMI, in which case PIL_NMI is retained.
+        *
+        * The only values we ever program into the %pil are 0,
+        * PIL_NORMAL_MAX and PIL_NMI.
+        *
+        * Since PIL_NMI is the largest %pil value and all bits are
+        * set in it (0xf), it doesn't matter what PIL_NORMAL_MAX
+        * actually is.
         */
        __asm__ __volatile__(
                "rdpr   %%pil, %0\n\t"