Re: [PATCH 2/2] cpuidle: exynos: add coupled cpuidle support for Exynos4210

From: Daniel Lezcano
Date: Wed Nov 12 2014 - 11:43:31 EST


On 11/12/2014 04:13 PM, Bartlomiej Zolnierkiewicz wrote:


Hi Bartlomiej,

[ cut ]

- using arch_send_wakeup_ipi_mask() instead of dsb_sev()
(this matches CPU hotplug code in arch/arm/mach-exynos/platsmp.c)

I am curious. You experienced very rare hangs after running the tests a
few hours, right ? Is the SEV replaced by the IPI solving the issue ? If
yes, how did you catch it ?

Rare hangs showed up after about 30-40 minutes of testing with the attached
app and script (running of "./cpuidle_state1_test.sh script 2 500" has never
completed on the umodified driver).

The problem turned out to be in the following loop waiting for CPU1 to get
stuck in the BOOT ROM:

/*
* Wait for cpu1 to get stuck in the boot rom
*/
while ((__raw_readl(BOOT_VECTOR) != 0) &&
!atomic_read(&cpu1_wakeup))
cpu_relax();

[ Removal of the loop fixed the problem. ]

Just for my personal information, do you know why ?

Using the SEV instead of the IPI was not a issue but it was changed to
match the existing Exynos platform code (exynos_boot_secondary() in
arch/arm/mach-exynos/platsmp.c) and as preparation for Exynos4412 (quad
core) support.

Ah, ok. Thanks for the info.

[ cut ]

+#ifdef CONFIG_ARM_EXYNOS_CPUIDLE
+ if (of_machine_is_compatible("samsung,exynos4210"))
+ exynos_cpuidle.dev.platform_data = &cpuidle_coupled_exynos_data;
+#endif

You should not add those #ifdef.

Without those #ifdef I get:

LD init/built-in.o
arch/arm/mach-exynos/built-in.o: In function `exynos_dt_machine_init':
/home/bzolnier/sam/linux-sprc/arch/arm/mach-exynos/exynos.c:334: undefined reference to `cpuidle_coupled_exynos_data'
make: *** [vmlinux] Error 1

when CONFIG_EXYNOS_CPU_SUSPEND is disabled.

Here, we are introducing some dependencies I tried to drop in the different drivers.

I looked more closely at the code and especially the 'cpuidle_coupled_exynos_data'. I don't think it is worth to have it because it adds more complexity and you have to define this structure to be visible from the drivers/cpuidle files.

I suggest you create an simple function in "pm.c"

int exynos_coupled_aftr(int cpu)
{
pre_enter...

if (!cpu)
cpu0_enter_aftr()
else
cpu1_powerdown()

post_enter...
}

and in the cpuidle driver itself, you just use the already existing anonymous callback 'exynos_enter_aftr' (and mutate it to conform the parameters).

You won't have to share any structure between the arch code and the cpuidle driver.


if (of_machine_is_compatible("samsung,exynos4210") ||
of_machine_is_compatible("samsung,exynos4212") ||
(of_machine_is_compatible("samsung,exynos4412") &&
diff --git a/arch/arm/mach-exynos/platsmp.c b/arch/arm/mach-exynos/platsmp.c

[ cut ]

- exynos_enter_aftr = (void *)(pdev->dev.platform_data);
+ if (of_machine_is_compatible("samsung,exynos4210")) {
+ exynos_cpuidle_pdata = pdev->dev.platform_data;
+
+ exynos_idle_driver.states[1].enter =
+ exynos_enter_coupled_lowpower;
+ exynos_idle_driver.states[1].exit_latency = 5000;
+ exynos_idle_driver.states[1].target_residency = 10000;
+ exynos_idle_driver.states[1].flags |= CPUIDLE_FLAG_COUPLED |
+ CPUIDLE_FLAG_TIMER_STOP;

I tried to remove those dynamic state allocation everywhere in the
different drivers. I would prefer to have another cpuidle_driver to be
registered with its states instead of overwriting the existing idle state.

struct cpuidle_driver exynos4210_idle_driver = {
.name = "exynos4210_idle",
.owner = THIS_MODULE,
.states = {
[0] = ARM_CPUIDLE_WFI_STATE,
[1] = {
.enter = exynos_enter_coupled_lowpower,
.exit_latency = 5000,
.target_residency = 10000,
.flags = CPUIDLE_FLAG_TIME_VALID |
CPUIDLE_FLAG_COUPLED |
CPUIDLE_FLAG_TIMER_STOP,
.name = "C1",
.desc = "ARM power down",
},
}
};


and then:

if (of_machine_is_compatible("samsung,exynos4210")) {
...
ret = cpuidle_register(&exynos4210_idle_driver,
cpu_online_mask);
...
}
...

OK, I will fix it but (if you are OK with it) I will make the code use
"exynos_coupled" naming instead of "exynos4210" one to not have to change
it later.

If we can reuse this mechanism, which I believe it is possible to, for
4420 and 5250. Then we will be able to refactor this out again.

Ok, sounds good.

I plan to add support for Exynos3250 next as it should be the simplest
(it is also dual core) and I need it for other reasons anyway. Exynos4412
(quad core) support requires more work but should also be doable.

When it comes to Exynos5250 I was thinking about disabling normal AFTR
mode support for it as according to my testing (on Arndale board) it has
never worked (at least in upstream kernels, I don't know about Linaro or
internal ones).

The AFTR state worked on my 5250 very well. It is a Arndale board.


Thanks for resurrecting the patch and providing the multi core idle support. I am too busy to refocus on that right now.

-- Daniel


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