Subject: [PATCH 1/3] ARM: EXYNOS: remove non-working AFTR mode support

From: [email-masked] (Tomasz Figa)
Date: Fri, 28 Jun 2013 12:11:24 +0200

Hi Daniel,

I've been fighting with this whole AFTR state as well, before Bartlomiej. 
Let me share my thoughts on this.

On Friday 28 of June 2013 11:57:25 Daniel Lezcano wrote:
> On 06/27/2013 08:10 PM, Bartlomiej Zolnierkiewicz wrote:
> > On Wednesday, June 26, 2013 12:36:12 PM Daniel Lezcano wrote:
> >> On 06/26/2013 12:13 PM, Bartlomiej Zolnierkiewicz wrote:
> >>> AFTR mode support was introduced by commit 67173ca ("ARM: EXYNOS: Add
> >>> support AFTR mode on EXYNOS4210") in v3.4 kernel.  Unfortunately even
> >>> in v3.4 kernel it hasn't worked as supposed and this is still the
> >>> case
> >>> with v3.10-rc6 (it probably wasn't noticed because CONFIG_CPU_IDLE is
> >>> not turned on by default):
> >>> 
> >>> - on revision 0 of Exynos4210 (Universal C210 board) it causes lockup
> >>> 
> >>>   (on this revision only one core is usable so entry to AFTR mode is
> >>>   always attempted because the code tries to go into AFTR mode when
> >>>   all
> >>>   other CPUs except CPU0 are offlined)
> >>> 
> >>> - on revision 1.1 of Exynos4210 (Trats board) it causes a lockup when
> >>> 
> >>>   CPU1 is offlined (i.e. echo 0 >
> >>>   /sys/devices/system/cpu/cpu1/online)
> >>> 
> >>> - on later Exynos4/5 SoCs wrong registers may be accessed when all
> >>> CPUs
> >>> 
> >>>   except CPU0 are offlined resulting in panic/lockup
> >>>   (REG_DIRECTGO_ADDR
> >>>   and REG_DIRECTGO_FLAG register selections was implemented only for
> >>>   Exynos4210)
> >>> 
> >>> Just remove AFTR mode support for now.
> >> 
> >> Ok, I will jump on the opportunity to talk about this state.
> >> 
> >> 1. I tried different ways to make the AFTR state to be entered with
> >> *both* cpu online. It goes successfully to this state. The CPU0 is
> >> correctly woken up but the CPU1 is never woken up, why is it happening
> >> ?
> >> 
> >> https://bugs.launchpad.net/linaro-landing-team-samsung/+bug/1171518
> > 
> > No idea here, AFTR doesn't work for me with upstream kernels even if
> > only one CPU is online.
> 
> What do you mean by "AFTR doesn't work" ? Is the kernel hanging ? The
> state is never reached ?

If you don't unplug all the CPUs >0 the state is obviously never reached. 
Otherwise the whole system hangs after it tries to enter this mode without 
any reaction for external events, other than reset.

> > Also the documentation says that before entering system-level
> > power-down
> > mode (such as AFTR) when multiple CPUs cores are used all other CPU
> > cores should stop interrupt service so I'm not sure how the way
> > attempted by you should work.
> 
> The cpu enters the idle mode with the interrupts disabled.

Hmm? What is supposed to wake it up then? AFAIK the whole idea of any idle 
or sleep is to sit in such low power mode until some interrupt fires (and so 
the name of the WFI, wait for interrupt, instruction).

> >> 2. The CPU1 hotplug bug should been fixed and if I am not wrong there
> >> is
> >> a patch somewhere fixing this.
> >> 
> >> https://bugs.launchpad.net/linaro-power-kernel/+bug/1171382
> > 
> > Unfortunately none of the patches there helps with my issues.
> > 
> >> 3. What is the fix for Exynos5 ?
> >> 
> >> https://bugs.launchpad.net/linaro-power-kernel/+bug/1171253
> >> 
> >> It sounds like depending on Hypervisor mode is enabled or not, the
> >> AFTR
> >> does not work correctly.
> > 
> > Sorry no idea here either.  On any SoCs later than EXYNOS4210 the
> > registers used for s3c_cpu_resume address and 0xFCBA0D10 magic number
> > may be different than EXYNOS4210 defaults (at least on EXYNOS4412 they
> > indeed are different, unfortunately I lack any info needed for EXYNOS5
> > support). You are lucky that it even works in some cases on EXYNOS5250.
> > 
> >> In other words, instead of removing the AFTR state I suggest to fix
> >> it:
> >> both core being online, split driver for exynos4 and 5.
> > 
> > My main problem is that with the upstream kernel even on EXYNOS4210
> > rev0 (only one core useable due to hardware issues) the kernel goes
> > into AFTR state for the first few times during boot and then it just
> > lockups (after going into cpu_do_idle() which is really
> > cpu_v7_do_idle()
> > and which does wfi call) and doesn't wake up CPU0. I have currently
> > no idea how to fix or debug it further.
> 
> I have an Origen 4210 board Ver A. and it works without problem with the
> AFTR mode (cpu1 unplugged).

Great!

Since benefits of this feature are rather questionable, especially when you 
consider all the maintenance burden caused by it, could you do some 
measurements to check if power saving thanks to this mode is of any 
significance?

> > The issue happens with every upstream kernel version tried (from v3.4
> > to v3.10-rc6).  Lockups also happen on EXYNOS4210 rev1.1 when CPU1 is
> > offlined by hand and then cpuidle driver tries to go into AFTR mode
> > (because by default it doesn't go into AFTR mode on any SoC except
> > EXYNOS4210 rev0).
> > 
> > I don't have EXYNOS4210 rev1.0 but it seems that in the upstream AFTR
> > mode has never worked (even on hardware that it was originally
> > developed
> > on) since its introduction in v3.4 (which was released on 20th May
> > 2012).
> > 
> > IOW for over the year nobody cared to make it work and I have currently
> > no fix at hand so the corrent upstream resolution is to just remove the
> > known non-working code and re-introduce it later when/if needed (I can
> > just disable it with a small fix but we don't keep such long-term
> > broken
> > code as placeholder in the upstream kernel).  If left as it is people
> > can hit the known issues and waste time debugging them, just like this
> > happenend for me [1].
> > 
> > If you have AFTR mode working (especially on EXYNOS4210) in Linaro
> > kernels please get fixes upstream ASAP. However I still wonder whether
> > the maintanance nightmare (bugs for different cases in your launchpad)
> > is worth gains over standard idle mode as the rumor around here is that
> > they are not that great (unfortunately no numbers were provided during
> > original feature addition).
> 
> It works forme with a vanilla kernel 3.10.0-rc7.

As Bartek already said, I haven't worked on any of our Exynos 4210 based 
boards since it got introduced in Linux 3.4, with exactly the same effect we 
described.

> Removing a feature because it seems not working is not a good solution.
> The right way is to investigate what is happening and why.

I can agree only partially. Keeping a feature that is broken and without 
any significant benefits does not make sense for me. Neither does putting 
efforts into fixing it, only to find that it is of no use.

However this is purely a speculation. Could you test on your Origen, on 
which it is supposed to work, if this feature is of any use?

Best regards,
Tomasz

> Thanks
>   -- Daniel
> 
> > --
> > Bartlomiej Zolnierkiewicz
> > Samsung R&D Institute Poland
> > Samsung Electronics
> > 
> > [1] Somebody enabled CONFIG_CPU_IDLE in the default config in one of
> > our
> > internal kernel trees on a target on which this feature "works" (since
> > CPUs are not hot-unplugged by default on all targets except EXYNOS4210
> > rev0 the code for AFTR is not used) and resulted in lockups on boot on
> > my default testing target. It took my long time to find out that
> > problem
> > is actually caused by just enabling exynos cpuidle driver.
> > 
> >> Thanks
> >> 
> >>   -- Daniel
> >>> 
> >>> Cc: Jaecheol Lee <[email-masked]>
> >>> Cc: Lorenzo Pieralisi <[email-masked]>
> >>> Cc: Amit Daniel Kachhap <[email-masked]>
> >>> Cc: Tomasz Figa <[email-masked]>
> >>> Cc: Kukjin Kim <[email-masked]>
> >>> Cc: Daniel Lezcano <[email-masked]>
> >>> Cc: "Rafael J. Wysocki" <[email-masked]>
> >>> Signed-off-by: Kyungmin Park <[email-masked]>
> >>> Signed-off-by: Bartlomiej Zolnierkiewicz <[email-masked]>
> >>> ---
> >>> 
> >>>  arch/arm/mach-exynos/cpuidle.c | 131
> >>>  +---------------------------------------- 1 file changed, 1
> >>>  insertion(+), 130 deletions(-)
> >>> 
> >>> diff --git a/arch/arm/mach-exynos/cpuidle.c
> >>> b/arch/arm/mach-exynos/cpuidle.c index 17a18ff..0a657ac 100644
> >>> --- a/arch/arm/mach-exynos/cpuidle.c
> >>> +++ b/arch/arm/mach-exynos/cpuidle.c
> >>> @@ -17,30 +17,11 @@
> >>> 
> >>>  #include <linux/time.h>
> >>>  
> >>>  #include <asm/proc-fns.h>
> >>> 
> >>> -#include <asm/smp_scu.h>
> >>> -#include <asm/suspend.h>
> >>> -#include <asm/unified.h>
> >>> 
> >>>  #include <asm/cpuidle.h>
> >>>  #include <mach/regs-clock.h>
> >>> 
> >>> -#include <mach/regs-pmu.h>
> >>> -
> >>> -#include <plat/cpu.h>
> >>> 
> >>>  #include "common.h"
> >>> 
> >>> -#define REG_DIRECTGO_ADDR	(samsung_rev() == EXYNOS4210_REV_1_1 ? \
> >>> -			S5P_INFORM7 : (samsung_rev() == EXYNOS4210_REV_1_0 ? \
> >>> -			(S5P_VA_SYSRAM + 0x24) : S5P_INFORM0))
> >>> -#define REG_DIRECTGO_FLAG	(samsung_rev() == EXYNOS4210_REV_1_1 ? \
> >>> -			S5P_INFORM6 : (samsung_rev() == EXYNOS4210_REV_1_0 ? \
> >>> -			(S5P_VA_SYSRAM + 0x20) : S5P_INFORM1))
> >>> -
> >>> -#define S5P_CHECK_AFTR		0xFCBA0D10
> >>> -
> >>> -static int exynos4_enter_lowpower(struct cpuidle_device *dev,
> >>> -				struct cpuidle_driver *drv,
> >>> -				int index);
> >>> -
> >>> 
> >>>  static DEFINE_PER_CPU(struct cpuidle_device,
> >>>  exynos4_cpuidle_device);
> >>>  
> >>>  static struct cpuidle_driver exynos4_idle_driver = {
> >>> 
> >>> @@ -48,117 +29,11 @@ static struct cpuidle_driver exynos4_idle_driver
> >>> = {>>> 
> >>>  	.owner			= THIS_MODULE,
> >>>  	.states = {
> >>>  	
> >>>  		[0] = ARM_CPUIDLE_WFI_STATE,
> >>> 
> >>> -		[1] = {
> >>> -			.enter			= exynos4_enter_lowpower,
> >>> -			.exit_latency		= 300,
> >>> -			.target_residency	= 100000,
> >>> -			.flags			= CPUIDLE_FLAG_TIME_VALID,
> >>> -			.name			= "C1",
> >>> -			.desc			= "ARM power down",
> >>> -		},
> >>> 
> >>>  	},
> >>> 
> >>> -	.state_count = 2,
> >>> +	.state_count = 1,
> >>> 
> >>>  	.safe_state_index = 0,
> >>>  
> >>>  };
> >>> 
> >>> -/* Ext-GIC nIRQ/nFIQ is the only wakeup source in AFTR */
> >>> -static void exynos4_set_wakeupmask(void)
> >>> -{
> >>> -	__raw_writel(0x0000ff3e, S5P_WAKEUP_MASK);
> >>> -}
> >>> -
> >>> -static unsigned int g_pwr_ctrl, g_diag_reg;
> >>> -
> >>> -static void save_cpu_arch_register(void)
> >>> -{
> >>> -	/*read power control register*/
> >>> -	asm("mrc p15, 0, %0, c15, c0, 0" : "=r"(g_pwr_ctrl) : : "cc");
> >>> -	/*read diagnostic register*/
> >>> -	asm("mrc p15, 0, %0, c15, c0, 1" : "=r"(g_diag_reg) : : "cc");
> >>> -	return;
> >>> -}
> >>> -
> >>> -static void restore_cpu_arch_register(void)
> >>> -{
> >>> -	/*write power control register*/
> >>> -	asm("mcr p15, 0, %0, c15, c0, 0" : : "r"(g_pwr_ctrl) : "cc");
> >>> -	/*write diagnostic register*/
> >>> -	asm("mcr p15, 0, %0, c15, c0, 1" : : "r"(g_diag_reg) : "cc");
> >>> -	return;
> >>> -}
> >>> -
> >>> -static int idle_finisher(unsigned long flags)
> >>> -{
> >>> -	cpu_do_idle();
> >>> -	return 1;
> >>> -}
> >>> -
> >>> -static int exynos4_enter_core0_aftr(struct cpuidle_device *dev,
> >>> -				struct cpuidle_driver *drv,
> >>> -				int index)
> >>> -{
> >>> -	unsigned long tmp;
> >>> -
> >>> -	exynos4_set_wakeupmask();
> >>> -
> >>> -	/* Set value of power down register for aftr mode */
> >>> -	exynos_sys_powerdown_conf(SYS_AFTR);
> >>> -
> >>> -	__raw_writel(virt_to_phys(s3c_cpu_resume), REG_DIRECTGO_ADDR);
> >>> -	__raw_writel(S5P_CHECK_AFTR, REG_DIRECTGO_FLAG);
> >>> -
> >>> -	save_cpu_arch_register();
> >>> -
> >>> -	/* Setting Central Sequence Register for power down mode */
> >>> -	tmp = __raw_readl(S5P_CENTRAL_SEQ_CONFIGURATION);
> >>> -	tmp &= ~S5P_CENTRAL_LOWPWR_CFG;
> >>> -	__raw_writel(tmp, S5P_CENTRAL_SEQ_CONFIGURATION);
> >>> -
> >>> -	cpu_pm_enter();
> >>> -	cpu_suspend(0, idle_finisher);
> >>> -
> >>> -#ifdef CONFIG_SMP
> >>> -	if (!soc_is_exynos5250())
> >>> -		scu_enable(S5P_VA_SCU);
> >>> -#endif
> >>> -	cpu_pm_exit();
> >>> -
> >>> -	restore_cpu_arch_register();
> >>> -
> >>> -	/*
> >>> -	 * If PMU failed while entering sleep mode, WFI will be
> >>> -	 * ignored by PMU and then exiting cpu_do_idle().
> >>> -	 * S5P_CENTRAL_LOWPWR_CFG bit will not be set automatically
> >>> -	 * in this situation.
> >>> -	 */
> >>> -	tmp = __raw_readl(S5P_CENTRAL_SEQ_CONFIGURATION);
> >>> -	if (!(tmp & S5P_CENTRAL_LOWPWR_CFG)) {
> >>> -		tmp |= S5P_CENTRAL_LOWPWR_CFG;
> >>> -		__raw_writel(tmp, S5P_CENTRAL_SEQ_CONFIGURATION);
> >>> -	}
> >>> -
> >>> -	/* Clear wakeup state register */
> >>> -	__raw_writel(0x0, S5P_WAKEUP_STAT);
> >>> -
> >>> -	return index;
> >>> -}
> >>> -
> >>> -static int exynos4_enter_lowpower(struct cpuidle_device *dev,
> >>> -				struct cpuidle_driver *drv,
> >>> -				int index)
> >>> -{
> >>> -	int new_index = index;
> >>> -
> >>> -	/* This mode only can be entered when other core's are offline */
> >>> -	if (num_online_cpus() > 1)
> >>> -		new_index = drv->safe_state_index;
> >>> -
> >>> -	if (new_index == 0)
> >>> -		return arm_cpuidle_simple_enter(dev, drv, new_index);
> >>> -	else
> >>> -		return exynos4_enter_core0_aftr(dev, drv, new_index);
> >>> -}
> >>> -
> >>> 
> >>>  static void __init exynos5_core_down_clk(void)
> >>>  {
> >>>  
> >>>  	unsigned int tmp;
> >>> 
> >>> @@ -209,10 +84,6 @@ static int __init exynos4_init_cpuidle(void)
> >>> 
> >>>  		device = &per_cpu(exynos4_cpuidle_device, cpu_id);
> >>>  		device->cpu = cpu_id;
> >>> 
> >>> -		/* Support IDLE only */
> >>> -		if (cpu_id != 0)
> >>> -			device->state_count = 1;
> >>> -
> >>> 
> >>>  		ret = cpuidle_register_device(device);
> >>>  		if (ret) {
> >>>  		
> >>>  			printk(KERN_ERR "CPUidle register device failed\n");