clear wakeup enable bit upon resuming from suspend

The FVP specific code that gets called after a cpu has been physically
powered on after having been turned off or suspended earlier does not
clear the PWRC.PWKUPR.WEN bit. Not doing so causes problems if: a cpu
is suspended, woken from suspend, powered down through a cpu_off call
& receives a spurious interrupt. Since the WEN bit is not cleared
after the cpu woke up from suspend, the spurious wakeup will power the
cpu on. Since the cpu_off call clears the jump address in the mailbox
this spurious wakeup will cause the cpu to crash.

This patch fixes this issue by clearing the WEN bit whenever a cpu is
powered up.

Change-Id: Ic91f5dffe1ed01d76bc7fc807acf0ecd3e38ce5b

docs/change-log.md

@@ -45,6 +45,9 @@ Detailed changes since last release
     instructions for how to contribute and update copyright text in all files to
     acknowledge contributors.
 
+*   The wake up enable bit in the FVP power controller is cleared when a cpu is
+    physically powered up to prevent a spurious wake up from a subsequent cpu
+    off state.
 
 ARM Trusted Firmware - version 0.2
 ==================================

drivers/power/fvp_pwrc.c

@@ -77,7 +77,7 @@ void fvp_pwrc_write_ppoffr(unsigned long mpidr)
 	bakery_lock_release(mpidr, &pwrc_lock);
 }
 
-void fvp_pwrc_write_pwkupr(unsigned long mpidr)
+void fvp_pwrc_set_wen(unsigned long mpidr)
 {
 	bakery_lock_get(mpidr, &pwrc_lock);
 	mmio_write_32(PWRC_BASE + PWKUPR_OFF,
@@ -85,6 +85,14 @@ void fvp_pwrc_write_pwkupr(unsigned long mpidr)
 	bakery_lock_release(mpidr, &pwrc_lock);
 }
 
+void fvp_pwrc_clr_wen(unsigned long mpidr)
+{
+	bakery_lock_get(mpidr, &pwrc_lock);
+	mmio_write_32(PWRC_BASE + PWKUPR_OFF,
+		      (unsigned int) mpidr);
+	bakery_lock_release(mpidr, &pwrc_lock);
+}
+
 void fvp_pwrc_write_pcoffr(unsigned long mpidr)
 {
 	bakery_lock_get(mpidr, &pwrc_lock);

drivers/power/fvp_pwrc.h

@@ -67,7 +67,8 @@ extern int fvp_pwrc_setup(void);
 extern void fvp_pwrc_write_pcoffr(unsigned long);
 extern void fvp_pwrc_write_ppoffr(unsigned long);
 extern void fvp_pwrc_write_pponr(unsigned long);
-extern void fvp_pwrc_write_pwkupr(unsigned long);
+extern void fvp_pwrc_set_wen(unsigned long);
+extern void fvp_pwrc_clr_wen(unsigned long);
 extern unsigned int fvp_pwrc_read_psysr(unsigned long);
 extern unsigned int fvp_pwrc_get_cpu_wkr(unsigned long);
 

plat/fvp/fvp_pm.c

@@ -251,7 +251,7 @@ int fvp_affinst_suspend(unsigned long mpidr,
 			 * Program the power controller to power this
 			 * cpu off and enable wakeup interrupts.
 			 */
-			fvp_pwrc_write_pwkupr(mpidr);
+			fvp_pwrc_set_wen(mpidr);
 			fvp_pwrc_write_ppoffr(mpidr);
 		}
 		break;
@@ -309,6 +309,12 @@ int fvp_affinst_on_finish(unsigned long mpidr,
 			write_cpuectlr(ectlr);
 		}
 
+		/*
+		 * Clear PWKUPR.WEN bit to ensure interrupts do not interfere
+		 * with a cpu power down unless the bit is set again
+		 */
+		fvp_pwrc_clr_wen(mpidr);
+
 		/* Zero the jump address in the mailbox for this cpu */
 		fvp_mboxes = (mailbox *) (TZDRAM_BASE + MBOX_OFF);
 		linear_id = platform_get_core_pos(mpidr);