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

[lorenzo.pieralisi@arm.com (Lorenzo Pieralisi)]

On Wed, Jul 17, 2013 at 01:57:30PM +0100, Daniel Lezcano wrote:
> On 07/11/2013 03:14 PM, Bartlomiej Zolnierkiewicz wrote:
> > 
> > Hi,
> > 
> > On Friday, June 28, 2013 11:47:49 PM Daniel Lezcano wrote:
> >> On 06/28/2013 06:27 PM, Bartlomiej Zolnierkiewicz wrote:
> >>> On Friday, June 28, 2013 01:20:09 PM Daniel Lezcano wrote:
> >>>> On 06/28/2013 12:11 PM, Tomasz Figa wrote:
> >>>>> Hi Daniel,
> >>>>>
> >>>>> I've been fighting with this whole AFTR state as well, before Bartlomiej. 
> >>>>> Let me share my thoughts on this.
> >>>>>
> >>
> >> [ ... ]
> >>
> >>>>>
> >>>>> 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.
> >>>>
> >>>> Need investigation.
> >>>>
> >>>> What is the exynos board version where that occurs ?
> >>>
> >>> Could you please tell me what exactly do you mean by that?
> >>>
> >>> I already wrote that we can reproduce the problem on EXYNOS4210 rev0
> >>> and rev1.1 (we don't have rev1.0). Tomek has also reproduced the problem
> >>> on some later SoCs (I hope that he can give you exact revisions).
> >>>
> >>> In our testing we didn't encounter the board on which the problem
> >>> doesn't occur. Our current working theory is that the problem may be
> >>> u-boot (or first stage bootloader) related.
> >>
> >> Ok, the status for what I know:
> >>
> >> Origen Exynos4210, board ver A: works for me
> >> Arndale Exynos5250: works for me but only if u-boot does not enable the
> >> hypervisor mode.
> >> Chromebook Exynos5250: works for me
> > 
> > I've also done some more testing. First I tested on some Exynos4412 devices
> > (M0 and SLP_PQ) and AFTR was not working on them. Then I got my hands on
> > Origen Exynos4210 (thanks to Tomek Figa for providing it) and AFTR is working
> > just fine on it. Finally I tried Trats board again but with the upstream
> > u-boot instead of our custom modified version (thanks to help from Lukasz
> > Majewski) and I found out that after this change AFTR works fine on it! It
> > also gives quite nice power savings (~80mA less current drawn in AFTR mode
> > compared to just WFI one).
> 
> Is the 80mA power saving comparing with:
> 
>  * (cpu0/cpu1 online) vs (cpu0 AFTR and cpu1 offline)
> or
>  * (cpu0 AFTR and cpu1 offline) vs (cpu0 WFI and cpu1 offline)
> 
> ?
> 
> > With the above findings it now seems that the issue is on our side and is
> > outside the kernel. Thanks for help with narrowing down the problem and
> > sorry for wasting your time.
> 
> May be we were not working on the same tree.
> 
> I am on the linux-pm-next tree.
> 
> Now the merge window occurred, the AFTR is no longer working on my board.
> 
> After git bisecting:
> 
> commit 87107d89052bcec1fe91b309631de4ed294a5171
> Author: Arnd Bergmann <arnd@arndb.de>
> Date:   Wed Jun 19 01:36:52 2013 +0900
> 
>     ARM: EXYNOS: Remove legacy L2X0 initialization
> 
>     Since Exynos is now supporting only DT-based boot, the old L2X0
>     initialization code is not needed anymore, so exynos4_l2x0_cache_init()
>     can be greatly simplified.
> 
>     Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>     Signed-off-by: Tomasz Figa <t.figa@samsung.com>
>     Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
>     Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
> 
> :040000 040000 79e1adfd6386256ba71b3f609592d5acf9c08222
> 9cb0026563b3b8657d906767493d26c501963269 M	arch
> 
> Reverting the patch solves the problem.
> 
> Any ideas ?

It is certainly a problem related to restoring L2 control registers in
plat-samsung/s5p-sleep.S, probably DT init misses some registers
(prefetch and power control) that are restored to zero values most
likely, or the cluster cannot be shut down owing to those values not
being programmed properly. Chander posted a patch to fix that but I could
not follow that thread, I have no idea where he got to and if that fixes
the issue, I think so.

Lorenzo