Date:   Wed, 15 Jun 2022 00:12:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tony Lindgren <tony@...mide.com>
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Subject: Re: [PATCH 34.5/36] cpuidle,omap4: Push RCU-idle into
 omap4_enter_lowpower()

On Mon, Jun 13, 2022 at 03:39:05PM +0300, Tony Lindgren wrote:
> OMAP4 uses full SoC suspend modes as idle states, as such it needs the
> whole power-domain and clock-domain code from the idle path.
> 
> All that code is not suitable to run with RCU disabled, as such push
> RCU-idle deeper still.
> 
> Signed-off-by: Tony Lindgren <tony@...mide.com>
> ---
> 
> Peter here's one more for your series, looks like this is needed to avoid
> warnings similar to what you did for omap3.

Thanks Tony!

I've had a brief look at omap2_pm_idle() and do I understand it right
that something like the below patch would reduce it to a simple 'WFI'?

What do I do with the rest of that code, because I don't think this
thing has a cpuidle driver to take over, effectively turning it into
dead code.

--- a/arch/arm/mach-omap2/pm24xx.c
+++ b/arch/arm/mach-omap2/pm24xx.c
@@ -126,10 +126,20 @@ static int omap2_allow_mpu_retention(voi
 	return 1;
 }
 
-static void omap2_enter_mpu_retention(void)
+static void omap2_do_wfi(void)
 {
 	const int zero = 0;
 
+	/* WFI */
+	asm("mcr p15, 0, %0, c7, c0, 4" : : "r" (zero) : "memory", "cc");
+}
+
+#if 0
+/*
+ * possible cpuidle implementation between WFI and full_retention above
+ */
+static void omap2_enter_mpu_retention(void)
+{
 	/* The peripherals seem not to be able to wake up the MPU when
 	 * it is in retention mode. */
 	if (omap2_allow_mpu_retention()) {
@@ -146,8 +157,7 @@ static void omap2_enter_mpu_retention(vo
 		pwrdm_set_next_pwrst(mpu_pwrdm, PWRDM_POWER_ON);
 	}
 
-	/* WFI */
-	asm("mcr p15, 0, %0, c7, c0, 4" : : "r" (zero) : "memory", "cc");
+	omap2_do_wfi();
 
 	pwrdm_set_next_pwrst(mpu_pwrdm, PWRDM_POWER_ON);
 }
@@ -161,6 +171,7 @@ static int omap2_can_sleep(void)
 
 	return 1;
 }
+#endif
 
 static void omap2_pm_idle(void)
 {
@@ -169,6 +180,7 @@ static void omap2_pm_idle(void)
 	if (omap_irq_pending())
 		return;
 
+#if 0
 	error = cpu_cluster_pm_enter();
 	if (error || !omap2_can_sleep()) {
 		omap2_enter_mpu_retention();
@@ -179,6 +191,9 @@ static void omap2_pm_idle(void)
 
 out_cpu_cluster_pm:
 	cpu_cluster_pm_exit();
+#else
+	omap2_do_wfi();
+#endif
 }
 
 static void __init prcm_setup_regs(void)

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