Re: [PATCH] ARM: dts: exynos4412-odroid-*: add workaround for CPUfreq/reboot issue

[Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>]

Hi,

On Tuesday, September 01, 2015 10:57:37 PM Krzysztof Kozlowski wrote:
> 2015-09-01 22:08 GMT+09:00 Marek Szyprowski <m.szyprowski@samsung.com>:
> > Exynos4412-based Odroid boards (X2, U3, U3+) don't reset PMIC
> > configuration during hardware reset. This causes serious issues with
> > CPUfreq, when ARM voltage is set below 1.0V. When one resets the board
> > when CPUfreq selected one of lower Exynos 4412 operating points (for
> > example: 200MHz and 0.9V), the bootloader crashes and it is not possible
> 
> s/crashes/hangs/ ? I did not observe a crash but a silent hang.
> 
> > to restart the board without turning power off.
> >
> > This patch provides a workaround for this issue by increasing the start
> > of valid range for vdd_arm regulator from 1.0V. After such change,
> > CPUfreq can still use lower operating points, but the voltage won't be
> > decreased below 1.0V and as a result it will be possible to reset board
> > at any time.
> >
> > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> 
> Do you plan to send the same fix for Trats2 board? Everything above
> applies there as well plus suspend is affected. The board cannot
> properly resume.
> 
> > ---
> > Hello,
> >
> > This issue was there from the beggining, but I was not able to reproduce
> > it. It has been already reported by Tobias in early Feb 2015
> > (http://www.spinics.net/lists/linux-samsung-soc/msg42294.html).
> > Recently, after CPUfreq changes (conversion to generic cpufreq dt and
> > enabling cpufreq in exynos_defconfig) it was much easier to observe this
> > issue.
> >
> > This workaround lets one still use CPUfreq and avoid unexpect board
> > crashes during reboot (both 'standard' and emergency).
> 
> Work-around looks nice and clean. It still allows to use cpufreq and
> reduce the energy consumption. The patch should go along with
> cpufreq-dt support for Exynos4412 which hopefully would be for v4.3.
> If cpufreq-dt for Exynos4412 won't get to v4.3 we can figure out
> proper solution, not a work-around.

This work-around is needed also for the old exynos-cpufreq driver
as the problem was already there on some Odroid setups (please read
the mail from February pointed by Marek for details).

We don't have a better fix for the time being so I think that it
should be merged now regardless of cpufreq-dt changes status.

> Anyway for the time being:
> Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
> 
> Thanks Marek,
> BR

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