powerpc: More fixes for lazy IRQ vs. idle

Looks like we still have issues with pSeries and Cell idle code
vs. the lazy irq state. In fact, the reset fixes that went upstream
are exposing the problem more by causing BUG_ON() to trigger (which
this patch turns into a WARN_ON instead).

We need to be careful when using a variant of low power state that
has the side effect of turning interrupts back on, to properly set
all the SW & lazy state to look as if everything is enabled before
we enter the low power state with MSR:EE off as we will return with
MSR:EE on. If not, we have a discrepancy of state which can cause
things to go very wrong later on.

This patch moves the logic into a helper and uses it from the
pseries and cell idle code. The power4/970 idle code already got
things right (in assembly even !) so I'm not touching it. The power7
"bare metal" idle code is subtly different and correct. Remains PA6T
and some hypervisor based Cell platforms which have questionable
code in there, but they are mostly dead platforms so I'll fix them
when I manage to get final answers from the respective maintainers
about how the low power state actually works on them.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: stable@vger.kernel.org [v3.4]

2 files changed, 16 insertions, 12 deletions

diff --git a/arch/powerpc/platforms/cell/pervasive.c b/arch/powerpc/platforms/cell/pervasive.c
index efdacc82957..d17e98bc0c1 100644
--- a/arch/powerpc/platforms/cell/pervasive.c
+++ b/arch/powerpc/platforms/cell/pervasive.c
@@ -42,11 +42,9 @@ static void cbe_power_save(void)
 {
 	unsigned long ctrl, thread_switch_control;
 
-	/*
-	 * We need to hard disable interrupts, the local_irq_enable() done by
-	 * our caller upon return will hard re-enable.
-	 */
-	hard_irq_disable();
+	/* Ensure our interrupt state is properly tracked */
+	if (!prep_irq_for_idle())
+		return;
 
 	ctrl = mfspr(SPRN_CTRLF);
 
@@ -81,6 +79,9 @@ static void cbe_power_save(void)
 	 */
 	ctrl &= ~(CTRL_RUNLATCH | CTRL_TE);
 	mtspr(SPRN_CTRLT, ctrl);
+
+	/* Re-enable interrupts in MSR */
+	__hard_irq_enable();
 }
 
 static int cbe_system_reset_exception(struct pt_regs *regs)
diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c
index e61483e8e96..c71be66bd5d 100644
--- a/arch/powerpc/platforms/pseries/processor_idle.c
+++ b/arch/powerpc/platforms/pseries/processor_idle.c
@@ -99,15 +99,18 @@ out:
 static void check_and_cede_processor(void)
 {
 	/*
-	 * Interrupts are soft-disabled at this point,
-	 * but not hard disabled. So an interrupt might have
-	 * occurred before entering NAP, and would be potentially
-	 * lost (edge events, decrementer events, etc...) unless
-	 * we first hard disable then check.
+	 * Ensure our interrupt state is properly tracked,
+	 * also checks if no interrupt has occurred while we
+	 * were soft-disabled
 	 */
-	hard_irq_disable();
-	if (!lazy_irq_pending())
+	if (prep_irq_for_idle()) {
 		cede_processor();
+#ifdef CONFIG_TRACE_IRQFLAGS
+		/* Ensure that H_CEDE returns with IRQs on */
+		if (WARN_ON(!(mfmsr() & MSR_EE)))
+			__hard_irq_enable();
+#endif
+	}
 }
 
 static int dedicated_cede_loop(struct cpuidle_device *dev,