arm, OMAP2: Use WFI for omap2_pm_idle()

arch_cpu_idle() is a very simple idle interface and exposes only a
single idle state and is expected to not require RCU and not do any
tracing/instrumentation.

As such, omap2_pm_idle() is not a valid implementation. Replace it
with a simple (shallow) omap2_do_wfi() call.

Omap2 doesn't have a cpuidle driver; but adding one would be the
recourse to (re)gain the other idle states.
Suggested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230112195541.721697850@infradead.org

arch/arm/mach-omap2/pm24xx.c

@@ -116,50 +116,12 @@ static int omap2_enter_full_retention(void)
 
 static int sti_console_enabled;
 
-static int omap2_allow_mpu_retention(void)
-{
-	if (!omap2xxx_cm_mpu_retention_allowed())
-		return 0;
-	if (sti_console_enabled)
-		return 0;
-
-	return 1;
-}
-
-static void omap2_enter_mpu_retention(void)
+static void omap2_do_wfi(void)
 {
 	const int zero = 0;
 
-	/* The peripherals seem not to be able to wake up the MPU when
-	 * it is in retention mode. */
-	if (omap2_allow_mpu_retention()) {
-		/* REVISIT: These write to reserved bits? */
-		omap_prm_clear_mod_irqs(CORE_MOD, PM_WKST1, ~0);
-		omap_prm_clear_mod_irqs(CORE_MOD, OMAP24XX_PM_WKST2, ~0);
-		omap_prm_clear_mod_irqs(WKUP_MOD, PM_WKST, ~0);
-
-		/* Try to enter MPU retention */
-		pwrdm_set_next_pwrst(mpu_pwrdm, PWRDM_POWER_RET);
-
-	} else {
-		/* Block MPU retention */
-		pwrdm_set_next_pwrst(mpu_pwrdm, PWRDM_POWER_ON);
-	}
-
 	/* WFI */
 	asm("mcr p15, 0, %0, c7, c0, 4" : : "r" (zero) : "memory", "cc");
-
-	pwrdm_set_next_pwrst(mpu_pwrdm, PWRDM_POWER_ON);
-}
-
-static int omap2_can_sleep(void)
-{
-	if (omap2xxx_cm_fclks_active())
-		return 0;
-	if (__clk_is_enabled(osc_ck))
-		return 0;
-
-	return 1;
 }
 
 static void omap2_pm_idle(void)
@@ -169,16 +131,7 @@ static void omap2_pm_idle(void)
 	if (omap_irq_pending())
 		return;
 
-	error = cpu_cluster_pm_enter();
-	if (error || !omap2_can_sleep()) {
-		omap2_enter_mpu_retention();
-		goto out_cpu_cluster_pm;
-	}
-
-	omap2_enter_full_retention();
-
-out_cpu_cluster_pm:
-	cpu_cluster_pm_exit();
+	omap2_do_wfi();
 }
 
 static void __init prcm_setup_regs(void)