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

Hi,

On Wednesday, November 12, 2014 05:43:20 PM Daniel Lezcano wrote:
> 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 ?

Unfortunately no. I just suspect that sometimes the BOOT_VECTOR register
is not zeroed (or is zeroed and then overwritten) because of the bug in
the firmware.

> [ 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.

The reason why the separate callbacks are needed is that the cpuidle
driver code uses coupled cpuidle barriers (I cannot move them to pm.c):

+static int exynos_enter_coupled_lowpower(struct cpuidle_device *dev,
+ struct cpuidle_driver *drv,
+ int index)
+{
+ int ret;
+
+ exynos_cpuidle_pdata->pre_enter_aftr();
+
+ /*
+ * Waiting all cpus to reach this point at the same moment
+ */
+ cpuidle_coupled_parallel_barrier(dev, &exynos_idle_barrier);
+
+ /*
+ * Both cpus will reach this point at the same time
+ */
+ ret = dev->cpu ? exynos_cpuidle_pdata->cpu1_powerdown()
+ : exynos_cpuidle_pdata->cpu0_enter_aftr();
+ if (ret)
+ index = ret;
+
+ /*
+ * Waiting all cpus to finish the power sequence before going further
+ */
+ cpuidle_coupled_parallel_barrier(dev, &exynos_idle_barrier);
+
+ exynos_cpuidle_pdata->post_enter_aftr();
+
+ return index;
+}

Could you please explain how the proposed pm.c::exynos_coupled_aftr()
would operate without these barriers?

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics



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