[PATCH RFT 2/2] arm: dts: disable CCI on exynos420 based arndale-octa

[Russell King - ARM Linux]

On Mon, Dec 01, 2014 at 10:03:28AM +0100, Krzysztof Kozlowski wrote:
> On pią, 2014-11-28 at 21:09 +0530, Abhilash Kesavan wrote:
> > Hello Krzysztof,
> > 
> > On Fri, Nov 28, 2014 at 8:49 PM, Krzysztof Kozlowski
> > <k.kozlowski at samsung.com> wrote:
> > > On pią, 2014-11-28 at 20:20 +0530, Abhilash Kesavan wrote:
> > >> The arndale-octa board was giving "imprecise external aborts" during
> > >> boot-up with MCPM enabled. CCI enablement of the boot cluster was found
> > >> to be the cause of these aborts (possibly because the secure f/w was not
> > >> allowing it). Hence, disable CCI for the arndale-octa board.
> > >>
> > >> Signed-off-by: Abhilash Kesavan <a.kesavan at samsung.com>
> > >> ---
> > >>  arch/arm/boot/dts/exynos5420-arndale-octa.dts |    4 ++++
> > >>  arch/arm/boot/dts/exynos5420.dtsi             |    2 +-
> > >>  2 files changed, 5 insertions(+), 1 deletion(-)
> > >
> > > I tested these 2 patches on Arndale Octa but there are no improvements.
> > > I still got imprecise aborts (some not fatal and sometimes killing init
> > > with full backtrace).
> > 
> > Thanks for testing. Are you testing this with exynos_defconfig with no
> > other changes ? Can you please confirm from the bootlog that MCPM and
> > CCI are not being initialized.
> > 
> That was exynos_defconfig with disabled DRM and enabled some debug,
> next-20141128.
> 
> When I tried only exynos_defconfig (with disabled DRM) it worked fine...
> So the imprecise aborts were caused by one of following debug options:
> 
> DEBUG_SECTION_MISMATCH
> DYNAMIC_DEBUG
> DEBUG_ATOMIC_SLEEP
> DEBUG_PREEMPT
> PROVE_LOCKING
> LOCKUP_DETECTOR
> DEBUG_LOCK_ALLOC
> PROVE_RCU
> DEBUG_RT_MUTEXES
> DEBUG_MUTEXES
> DEBUG_SPINLOCK
> DEBUG_LIST
> DEBUG_PAGEALLOC
> SPARSE_RCU_POINTER
> DEBUG_FS
> PM_DEBUG
> PM_ADVANCED_DEBUG
> GPIO_SYSFS
> 
> > Can you remove these 2 patches and on linux-next check if you are
> > getting aborts even with 5420_MCPM disabled.
> 
> I tried this already and imprecise aborts shown, however with my
> debugging options above.
> 
> Overall the patches seems to work properly (although the debugging issue
> needs to be resolved still), so:
> 
> On Arndale Octa (Exynos 5420):
> Tested-by: Krzysztof Kozlowski <k.kozlowski at samsung.com>

Reading this message, it seems that this should *not* be given a tested-by,
because it seems from what you've reported above, they don't work correctly.

If you have to turn debugging options off in order to get the kernel to
apparently run correctly after applying some patches, it means those
patches themselves are probably buggy, rather than the debug itself
being buggy.

I'd suggest that you have some further work to do (a manual bisect of the
config options you've disabled) to discover which is the cause of the
problem.

It could be that the code introduces something like a use-after-free bug.

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