[PATCH 1/2] ARM: dts: sun4i: a10-lime: Override and remove 1008MHz OPP setting

[Siarhei Siamashka]

On Thu, 19 Mar 2015 16:17:30 +0800
Chen-Yu Tsai <wens at csie.org> wrote:

> On Thu, Mar 19, 2015 at 2:57 PM, Siarhei Siamashka
> <siarhei.siamashka at gmail.com> wrote:
> > On Thu, 19 Mar 2015 10:39:32 +0800
> > Chen-Yu Tsai <wens at csie.org> wrote:
> >
> >> The Olimex A10-Lime is known to be unstable when running at 1008MHz.
> >>
> >> Signed-off-by: Chen-Yu Tsai <wens at csie.org>
> >> ---
> >>  arch/arm/boot/dts/sun4i-a10-olinuxino-lime.dts | 14 ++++++++++++++
> >>  1 file changed, 14 insertions(+)
> >>
> >> diff --git a/arch/arm/boot/dts/sun4i-a10-olinuxino-lime.dts b/arch/arm/boot/dts/sun4i-a10-olinuxino-lime.dts
> >> index 31dc2f1c3870..16ecb8938e19 100644
> >> --- a/arch/arm/boot/dts/sun4i-a10-olinuxino-lime.dts
> >> +++ b/arch/arm/boot/dts/sun4i-a10-olinuxino-lime.dts
> >> @@ -74,6 +74,20 @@
> >>       status = "okay";
> >>  };
> >>
> >> +&cpu0 {
> >> +     /* The A10-Lime is known to be unstable when running at 1008 MHz */
> >> +     operating-points = <
> >> +             /* kHz    uV */
> >> +             960000  1400000
> >> +             912000  1400000
> >> +             864000  1300000
> >> +             720000  1200000
> >> +             528000  1100000
> >> +             312000  1000000
> >> +             144000  900000
> >> +             >;
> >> +};
> >> +
> >>  &ehci0 {
> >>       status = "okay";
> >>  };
> >
> > Thanks for the patch. At least it should make my A10-OLinuXino-LIME
> > working without obvious failures out of the box (the U-Boot is still
> > another story though and there is a gap during boot up when the board
> > is running with unreliable settings, but the probability of a failure
> > is rather low).
> >
> > I should also mention that using 960MHz @1.4V does not fail, but it does
> > not have any safety headroom either (the cyan 'sun4i_poorlime' line
> > on the plot):
> >
> >     http://people.freedesktop.org/~siamashka/files/20140512/sunxi-cpufreq-plot.png
> >
> > On the other hand, my board is on the worst part of the spectrum (many
> > other a10-lime boards do not fail even at 1008MHz), so maybe having
> > extra safety headroom is less necessary.
> >
> > An interesting question is whether the same problem may be reproducible
> > on the Allwinner A10 devices other than A10-OLinuXino-LIME. My original
> > problem report
> >
> >     https://www.mail-archive.com/linux-sunxi@googlegroups.com/msg04343.html
> >
> > mentioned the A10-OLinuXino-LIME rev.A and introduced some sort of
> > a bias by itself. At least I have seen people saying something like
> > "my a10-lime revision is not rev.A, so it's none of my concern and
> > I'm not going to bother running any tests". So far we have accumulated
> > reports from 4 or 5 people having this reliability problem on their
> > A10-OLinuXino-LIME (various revisions, not just rev.A), but not
> > much from the other boards owners.
> >
> > Anyway, this particular patch is
> > Tested-by: Siarhei Siamashka <siarhei.siamashka at gmail.com>
> > Acked-by: Siarhei Siamashka <siarhei.siamashka at gmail.com>
> 
> Good to hear it works. Did you test all the settings?

You have nailed it. I was about to send the results of the full
round of tests after running them a bit longer and revoke the
initial Tested-by.

Turns out that the 312MHz and 144MHz operating points fail to work
reliable and tend to deadlock:

Testing CPU 0
  960 MHz ............................................................ OK
  912 MHz ............................................................ OK
  864 MHz ............................................................ OK
  720 MHz ............................................................ OK
  528 MHz ............................................................ OK
  312 MHz ............................................................ OK
  144 MHz Write failed: Broken pipe

Testing CPU 0
  960 MHz ............................................................ OK
  912 MHz ............................................................ OK
  864 MHz ............................................................ OK
  720 MHz ............................................................ OK
  528 MHz ............................................................ OK
  312 MHz .................Write failed: Broken pipe


> I copied the wrong settings, from sun5i-a13.dtsi instead of sun4i-a10.dtsi.

I guess, this explains the problems at lower operating points.

> I'll send a fixed version later.

Thanks.

-- 
Best regards,
Siarhei Siamashka