powerpc: Document how we set AIL on guest kernels

I spent ten minutes scratching my head, trying to work out where we
enabled relocation on interrupts for guest kernels. Expand the doco to
make it clear.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 6943390..75f94ae 100644 (file)
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -201,7 +201,11 @@ static void cpu_ready_for_interrupts(void)
        /* Set IR and DR in PACA MSR */
        get_paca()->kernel_msr = MSR_KERNEL;
 
-       /* Enable AIL if supported */
+       /*
+        * Enable AIL if supported, and we are in hypervisor mode. If we are
+        * not in hypervisor mode, we enable relocation-on interrupts later
+        * in pSeries_setup_arch() using the H_SET_MODE hcall.
+        */
        if (cpu_has_feature(CPU_FTR_HVMODE) &&
            cpu_has_feature(CPU_FTR_ARCH_207S)) {
                unsigned long lpcr = mfspr(SPRN_LPCR);