[PATCH] Exynos4: cpuidle: support dual CPUs with AFTR state

[Bartlomiej Zolnierkiewicz]

Hi,

On Friday, May 30, 2014 01:34:45 PM Tomasz Figa wrote:
> Hi Daniel,
> 
> On 30.05.2014 11:30, Daniel Lezcano wrote:
> > On 04/24/2014 07:42 PM, Tomasz Figa wrote:
> >> Hi Daniel,
> >>
> >> Please see my comments inline.
> >>
> >> Btw. Please fix your e-mail composer to properly wrap your messages
> >> around 7xth column, as otherwise they're hard to read.
> >>
> >> On 04.04.2014 11:48, Daniel Lezcano wrote:
> >>> The following driver is for exynos4210. I did not yet finished the
> >>> other boards, so
> >>> I created a specific driver for 4210 which could be merged later.
> >>>
> >>> The driver is based on Colin Cross's driver found at:
> >>>
> >>> https://android.googlesource.com/kernel/exynos/+/e686b1ec67423c40b4fdf811f9a4dfa3b393a010%5E%5E!/
> >>>
> >>>
> >>>
> >>> This one was based on a 3.4 kernel and an old API.
> >>>
> >>> It has been refreshed, simplified and based on the recent code cleanup
> >>> I sent
> >>> today.
> >>>
> >>> The AFTR could be entered when all the cpus (except cpu0) are down. In
> >>> order to
> >>> reach this situation, the couple idle states are used.
> >>>
> >>> There is a sync barrier at the entry and the exit of the low power
> >>> function. So
> >>> all cpus will enter and exit the function at the same time.
> >>>
> >>> At this point, CPU0 knows the other cpu will power down itself. CPU0
> >>> waits for
> >>> the CPU1 to be powered down and then initiate the AFTR power down
> >>> sequence.
> >>>
> >>> No interrupts are handled by CPU1, this is why we switch to the timer
> >>> broadcast
> >>> even if the local timer is not impacted by the idle state.
> >>>
> >>> When CPU0 wakes up, it powers up CPU1 and waits for it to boot. Then
> >>> they both
> >>> exit the idle function.
> >>>
> >>> This driver allows the exynos4210 to have the same power consumption
> >>> at idle
> >>> time than the one when we have to unplug CPU1 in order to let CPU0 to
> >>> reach
> >>> the AFTR state.
> >>>
> >>> This patch is a RFC because, we have to find a way to remove the macros
> >>> definitions and cpu powerdown function without pulling the arch
> >>> dependent
> >>> headers.
> >>>
> >>> Signed-off-by: Daniel Lezcano <daniel.lezcano at linaro.org>
> >>> ---
> >>>   arch/arm/mach-exynos/common.c        |   11 +-
> >>>   drivers/cpuidle/Kconfig.arm          |    8 ++
> >>>   drivers/cpuidle/Makefile             |    1 +
> >>>   drivers/cpuidle/cpuidle-exynos4210.c |  226
> >>> ++++++++++++++++++++++++++++++++++
> > 
> > [ ... ]
> > 
> > 
> >> Otherwise, I quite like the whole idea. I need to play a bit with CPU
> >> hotplug and PMU to verify that things couldn't really be simplified a
> >> bit, but in general this looks reasonably.
> > 
> > Hi Tomasz,
> > 
> > did you have time to look at this simplification ?
> 
> Unfortunately I got preempted with other things to do and now I'm on
> vacation. I worked a bit with Bart (added on CC) on this and generally
> the conclusion was that all the things are necessary. He was also
> working to extend the driver to support Exynos4x12.
> 
> Bart, has anything interesting showed up since we talked about this last
> time?

Since we last looked into this I have fixed the "standard" AFTR support
for Exynos3250 and started to work on adding Exynos3250 support to this
driver (as Exynos3250 support has bigger priority than Exynos4x12 one).
Unfortunately I also got preempted with other things so it is still
unfinished and doesn't work yet.  Moreover I had no possibility to test
the new driver on Exynos4210 based Origen yet (I hope to do this next
week).

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