From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Fri, 9 Jul 2010 05:30:22 +0000 (+1000)
Subject: powerpc/book3e: Don't re-trigger decrementer on lazy irq restore
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e8775d4aa17d70d123814e68a6a51bbea50e5c16;p=linux-beck.git

powerpc/book3e: Don't re-trigger decrementer on lazy irq restore

The decrementer on BookE acts as a level interrupt and doesn't
need to be re-triggered when going negative. It doesn't go
negative anyways (unless programmed to auto-reload with a
negative value) as it stops when reaching 0.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 77be3d058a65..fa6f38525801 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -159,8 +159,17 @@ notrace void raw_local_irq_restore(unsigned long en)
 	 * use local_paca instead of get_paca() to avoid preemption checking.
 	 */
 	local_paca->hard_enabled = en;
+
+#ifndef CONFIG_BOOKE
+	/* On server, re-trigger the decrementer if it went negative since
+	 * some processors only trigger on edge transitions of the sign bit.
+	 *
+	 * BookE has a level sensitive decrementer (latches in TSR) so we
+	 * don't need that
+	 */
 	if ((int)mfspr(SPRN_DEC) < 0)
 		mtspr(SPRN_DEC, 1);
+#endif /* CONFIG_BOOKE */
 
 	/*
 	 * Force the delivery of pending soft-disabled interrupts on PS3.