[PATCH] ARM: omap2+: Revert omap-smp.c changes resetting cpu1 during boot

Wed Feb 15 14:13:19 PST 2017

On 02/15/2017 01:12 PM, Tony Lindgren wrote:
> * Tony Lindgren <tony at atomide.com> [170215 10:40]:
>> * Tony Lindgren <tony at atomide.com> [170214 11:39]:
>>> * Tony Lindgren <tony at atomide.com> [170213 13:51]:
>>>> Commit 3251885285e1 ("ARM: OMAP4+: Reset CPU1 properly for kexec") started
>>>> resetting cpu1 because of a kexec boot issue I was seeing earlier in 2016
>>>> on omap4 when doing kexec boot between two different kernel versions. The
>>>> booted kernel ended up trying to use the old kernel start-up address unless
>>>> cpu1 was reset before configuring the cpu1 start-up address.
>>>>
>>>> It seems the reset part was not correct but probably working around some
>>>> other issue. I have not been able to reproduce this issue any longer despite
>>>> testing with backported patches back to v4.6 kernel. So it is possible this
>>>> issue was caused by other work in progress kexec patches I had applied. Or
>>>> it is possible some other fixes have made the issue go way.
>>>>
>>>> The unconditional reset of cpu1 can cause issues booting some devices. For
>>>> example, bootloader configured secure OS running on cpu1 will fail as the
>>>> configuration is not preserved as reported by Andrew F. Davis <afd at ti.com>.
>>>>
>>>> Let's fix the issue by reverting the cpu1 reset parts. If it turns out we
>>>> still need to reset cpu1 in some cases, we can add it back and do it
>>>> conditionally.
>>>
>>> Actually with this I'm now seeing cpu1 not come up after a suspend/resume
>>> cycle on duovero:
>>>
>>> [  118.257415] CPU1: shutdown
>>> [  118.294616] Error taking CPU1 up: -2
>>> [  118.299072] PM: noirq resume of devices complete after 3.723 msecs
>>> [  118.303802] PM: early resume of devices complete after 3.723 msecs
>>>
>>> So this issue needs to be investigated more.
>>
>> And then today the omap4 suspend/resume issue is no longer reproducable..
>> Go figure.
>>
>> But then doing more testing I noticed that also omap5 needs the reset.
>> Without it we get the following on omap5-uevm doing a kexec boot. So clearly
>> the reset cannot be just removed at least for omap4 and omap5.
> 
> And also the same issue happens doing kexec on beagle-x15 naturally if
> the cpu1 reset is removed.
> 

When a core actually powers up it idles in ROM code waiting for
OMAP_AUX_CORE_BOOT_0 to be set. When we shutdown a core it is not really
powered off, we just let it spin in omap4_cpu_die() or
omap4_secondary_startup() waiting on OMAP_AUX_CORE_BOOT_0, just like if
it were still trapped in ROM after a reset.

The issue with this fake startup idle loop is that, unlike the ROM based
startup idle loop, these do *not* jump to the address we stored in
OMAP_AUX_CORE_BOOT_1, they just make the assumption that they can safely
jump to the kernel startup function.

So when we tell this core to boot, and it is not in the real ROM startup
loop, it breaks stuff as it jumps to the old kernel's
secondary_startup() even though we gave it the correct address in
OMAP_AUX_CORE_BOOT_1.

Reseting the core to put it back in the real ROM idle loop is wrong, the
two idle loop functions above should be fixed to respect the address in
OMAP_AUX_CORE_BOOT_1 and not to make assumptions, this should take care
of the kexec failure in a sane way.

Andrew

> Regards,
> 
> Tony
> 
>> 8< ---------------------
>> [    0.156796] CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
>> [    0.163396] Setting up static identity map for 0x80100000 - 0x80100070
>> [    0.172246] smp: Bringing up secondary CPUs ...
>> [    0.178970] Unable to handle kernel NULL pointer dereference at virtual address 00000000
>> [    0.178974] pgd = c0004000
>> [    0.178977] [00000000] *pgd=00000000
>> [    0.178990] Internal error: Oops: 80000005 [#1] SMP ARM
>> [    0.178995] Modules linked in:
>> [    0.179005] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.10.0-rc8-next-20170215+ #120
>> [    0.179008] Hardware name: Generic OMAP5 (Flattened Device Tree)
>> [    0.179013] task: ee0c8ec0 task.stack: ee0ca000
>> [    0.179018] PC is at 0x0
>> [    0.179029] LR is at omap4_cpu_die+0x58/0x98
>> [    0.179034] pc : [<00000000>]    lr : [<c01243dc>]    psr: 60000093
>> [    0.179034] sp : ee0cbfb8  ip : 00000000  fp : 00000000
>> [    0.179038] r10: 00000000  r9 : c0d50569  r8 : 00000000
>> [    0.179042] r7 : c0c76448  r6 : c0d0792c  r5 : 00000001  r4 : c0b08054
>> [    0.179046] r3 : 00000001  r2 : f0880000  r1 : 00000003  r0 : 00000001
>> [    0.179051] Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment none
>> [    0.179055] Control: 10c5387d  Table: 8000406a  DAC: 00000051
>> [    0.179059] Process swapper/1 (pid: 0, stack limit = 0xee0ca218)
>> [    0.179063] Stack: (0xee0cbfb8 to 0xee0cc000)
>> [    0.179068] bfa0:                                                       00000000 00000000
>> [    0.179075] bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>> [    0.179082] bfe0: 00000000 00000000 00000000 00000000 00000013 00000000 681b0041 cf3e4021
>> [    0.179092] [<c01243dc>] (omap4_cpu_die) from [<00000000>] (  (null))
>> [    0.179098] Code: bad PC value
>> [    0.179115] ---[ end trace e14406c260ce69db ]---
>> [    0.179121] Kernel panic - not syncing: Attempted to kill the idle task!
>> [    0.179135] CPU0: stopping
>> [    0.179141] ---[ end Kernel panic - not syncing: Attempted to kill the idle task!
>> [    0.339715] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G      D         4.10.0-rc8-next-20170215+ #120
>> [    0.348927] Hardware name: Generic OMAP5 (Flattened Device Tree)
>> [    0.355112] [<c0110228>] (unwind_backtrace) from [<c010c224>] (show_stack+0x10/0x14)
>> [    0.363083] [<c010c224>] (show_stack) from [<c04ca860>] (dump_stack+0xac/0xe0)
>> [    0.370513] [<c04ca860>] (dump_stack) from [<c010e72c>] (handle_IPI+0x358/0x3f8)
>> [    0.378120] [<c010e72c>] (handle_IPI) from [<c01015a4>] (gic_handle_irq+0x9c/0xb8)
>> [    0.385909] [<c01015a4>] (gic_handle_irq) from [<c083b270>] (__irq_svc+0x70/0x98)
>> [    0.393602] Exception stack(0xc0d01f38 to 0xc0d01f80)
>> [    0.398794] 1f20:                                                       c0108284 00000000
>> [    0.407205] 1f40: 00000000 00000000 c0d00000 c0d07994 c0d0792c c0c76448 c0d08560 c0d50569
>> [    0.415616] 1f60: 00000000 00000000 00000000 c0d01f88 c0108284 c0108288 60000013 ffffffff
>> [    0.424032] [<c083b270>] (__irq_svc) from [<c0108288>] (arch_cpu_idle+0x20/0x3c)
>> [    0.431643] [<c0108288>] (arch_cpu_idle) from [<c0190bc4>] (do_idle+0x164/0x218)
>> [    0.439251] [<c0190bc4>] (do_idle) from [<c0190ffc>] (cpu_startup_entry+0x18/0x1c)
>> [    0.447040] [<c0190ffc>] (cpu_startup_entry) from [<c0c00c40>] (start_kernel+0x35c/0x3d4)
>> [    0.455451] [<c0c00c40>] (start_kernel) from [<8000807c>] (0x8000807c)
>> --
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