AT91: pm: use plain cpu_do_idle() for "wait for interrupt"

For power management at91_pm_enter() routine, use the cpu_do_idle() for a
rock solid "wait for interrupt" implementation.
For AT91SAM9 ARM 926 based chips, we can exceed the cache line length as
we can access RAM even while in self-refresh mode.
We keep plain access to CP15 for at91rm9200 as this feature is not
available: instructions have to be in a single cache line.
Signed-off-by: NNicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/pm.c

@@ -258,16 +258,18 @@ static int at91_pm_enter(suspend_state_t state)
 			 * NOTE: the Wait-for-Interrupt instruction needs to be
 			 * in icache so no SDRAM accesses are needed until the
 			 * wakeup IRQ occurs and self-refresh is terminated.
+			 * For ARM 926 based chips, this requirement is weaker
+			 * as at91sam9 can access a RAM in self-refresh mode.
 			 */
 			asm("b 1f; .align 5; 1:");
 			asm("mcr p15, 0, r0, c7, c10, 4");	/* drain write buffer */
 			saved_lpr = sdram_selfrefresh_enable();
-			asm("mcr p15, 0, r0, c7, c0, 4");	/* wait for interrupt */
+			wait_for_interrupt_enable();
 			sdram_selfrefresh_disable(saved_lpr);
 			break;
 
 		case PM_SUSPEND_ON:
-			asm("mcr p15, 0, r0, c7, c0, 4");	/* wait for interrupt */
+			cpu_do_idle();
 			break;
 
 		default:

arch/arm/mach-at91/pm.h

@@ -21,6 +21,7 @@ static inline u32 sdram_selfrefresh_enable(void)
 }
 
 #define sdram_selfrefresh_disable(saved_lpr)	at91_sys_write(AT91_SDRAMC_LPR, saved_lpr)
+#define wait_for_interrupt_enable()		asm("mcr p15, 0, r0, c7, c0, 4")
 
 #elif defined(CONFIG_ARCH_AT91CAP9)
 #include <mach/at91cap9_ddrsdr.h>
@@ -38,6 +39,7 @@ static inline u32 sdram_selfrefresh_enable(void)
 }
 
 #define sdram_selfrefresh_disable(saved_lpr)	at91_ramc_write(0, AT91_DDRSDRC_LPR, saved_lpr)
+#define wait_for_interrupt_enable()		cpu_do_idle()
 
 #elif defined(CONFIG_ARCH_AT91SAM9G45)
 #include <mach/at91sam9_ddrsdr.h>
@@ -74,6 +76,7 @@ static inline u32 sdram_selfrefresh_enable(void)
 		at91_ramc_write(0, AT91_DDRSDRC_LPR, saved_lpr0); \
 		at91_ramc_write(1, AT91_DDRSDRC_LPR, saved_lpr1); \
 	} while (0)
+#define wait_for_interrupt_enable()		cpu_do_idle()
 
 #else
 #include <mach/at91sam9_sdramc.h>
@@ -98,5 +101,6 @@ static inline u32 sdram_selfrefresh_enable(void)
 }
 
 #define sdram_selfrefresh_disable(saved_lpr)	at91_ramc_write(0, AT91_SDRAMC_LPR, saved_lpr)
+#define wait_for_interrupt_enable()		cpu_do_idle()
 
 #endif