Re: [PATCH 34.5/36] cpuidle,omap4: Push RCU-idle into omap4_enter_lowpower()

Peter Zijlstra
2022-06-14T22:12:42Z

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@atomide.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)