Re: [PATCH 1/6] clk: add CLK_RECALC_NEW_RATES clock flag for Exynos cpu clock support

Michael Turquette
2015-06-20T19:14:00Z

Quoting Krzysztof Kozlowski (2015-06-20 03:01:12)
> W dniu 19.06.2015 o 23:53, Michael Turquette pisze:
> > Quoting Bartlomiej Zolnierkiewicz (2015-06-19 05:35:23)
> >> On Friday, June 19, 2015 01:19:06 PM Bartlomiej Zolnierkiewicz wrote:
> >>>
> >>> Hi,
> >>>
> >>> On Thursday, June 18, 2015 12:58:46 PM Michael Turquette wrote:
> >>>> Quoting Sylwester Nawrocki (2015-05-13 07:13:13)
> >>>>> On 03/04/15 18:43, Bartlomiej Zolnierkiewicz wrote:
> >>>>>> This flag is needed to fix the issue with wrong dividers being setup
> >>>>>> by Common Clock Framework when using the new Exynos cpu clock support.
> >>>>>>
> >>>>>> The issue happens because clk_core_set_rate_nolock() calls
> >>>>>> clk_calc_new_rates(clk, rate) before both pre/post clock notifiers have
> >>>>>> a chance to run. In case of Exynos cpu clock support pre/post clock
> >>>>>> notifiers are registered for mout_apll clock which is a parent of armclk
> >>>>>> cpu clock and dividers are modified in both pre and post clock notifier.
> >>>>>> This results in wrong dividers values being later programmed by
> >>>>>> clk_change_rate(top). To workaround the problem CLK_RECALC_NEW_RATES
> >>>>>> flag is added and it is set for mout_apll clock later so the correct
> >>>>>> divider values are re-calculated after both pre and post clock notifiers
> >>>>>> had run.
> >>>>>>
> >>>>>> For example when using "performance" governor on Exynos4210 Origen board
> >>>>>> the cpufreq-dt driver requests to change the frequency from 1000MHz to
> >>>>>> 1200MHz and after the change state of the relevant clocks is following:
> >>>>>>
> >>>>>> Without use of CLK_GET_RATE_NOCACHE flag:
> >>>>>>
> >>>>>> fout_apll rate: 1200000000
> >>>>>> fout_apll_div_2 rate: 600000000
> >>>>>> mout_clkout_cpu rate: 600000000
> >>>>>> div_clkout_cpu rate: 600000000
> >>>>>> clkout_cpu rate: 600000000
> >>>>>> mout_apll rate: 1200000000
> >>>>>> armclk rate: 1200000000
> >>>>>> mout_hpm rate: 1200000000
> >>>>>> div_copy rate: 300000000
> >>>>>> div_hpm rate: 300000000
> >>>>>> mout_core rate: 1200000000
> >>>>>> div_core rate: 1200000000
> >>>>>> div_core2 rate: 1200000000
> >>>>>> arm_clk_div_2 rate: 600000000
> >>>>>> div_corem0 rate: 300000000
> >>>>>> div_corem1 rate: 150000000
> >>>>>> div_periph rate: 300000000
> >>>>>> div_atb rate: 300000000
> >>>>>> div_pclk_dbg rate: 150000000
> >>>>>> sclk_apll rate: 1200000000
> >>>>>> sclk_apll_div_2 rate: 600000000
> >>>>>>
> >>>>>>
> >>>>>> With use of CLK_GET_RATE_NOCACHE flag:
> >>>>>>
> >>>>>> fout_apll rate: 1200000000
> >>>>>> fout_apll_div_2 rate: 600000000
> >>>>>> mout_clkout_cpu rate: 600000000
> >>>>>> div_clkout_cpu rate: 600000000
> >>>>>> clkout_cpu rate: 600000000
> >>>>>> mout_apll rate: 1200000000
> >>>>>> armclk rate: 1200000000
> >>>>>> mout_hpm rate: 1200000000
> >>>>>> div_copy rate: 200000000
> >>>>>> div_hpm rate: 200000000
> >>>>>> mout_core rate: 1200000000
> >>>>>> div_core rate: 1200000000
> >>>>>> div_core2 rate: 1200000000
> >>>>>> arm_clk_div_2 rate: 600000000
> >>>>>> div_corem0 rate: 300000000
> >>>>>> div_corem1 rate: 150000000
> >>>>>> div_periph rate: 300000000
> >>>>>> div_atb rate: 240000000
> >>>>>> div_pclk_dbg rate: 120000000
> >>>>>> sclk_apll rate: 150000000
> >>>>>> sclk_apll_div_2 rate: 75000000
> >>>>>>
> >>>>>> Without this change cpufreq-dt driver showed ~10 mA larger energy
> >>>>>> consumption when compared to cpufreq-exynos one when "performance"
> >>>>>> cpufreq governor was used on Exynos4210 SoC based Origen board.
> >>>>>>
> >>>>>> This issue was probably meant to be workarounded by use of
> >>>>>> CLK_GET_RATE_NOCACHE and CLK_DIVIDER_READ_ONLY clock flags in
> >>>>>> the original Exynos cpu clock patchset (in "[PATCH v12 6/6] clk:
> >>>>>> samsung: remove unused clock aliases and update clock flags" patch)
> >>>>>> but usage of these flags is not sufficient to fix the issue observed.
> >>>>>>
> >>>>>> Cc: Thomas Abraham <thomas.ab@samsung.com>
> >>>>>> Cc: Tomasz Figa <tomasz.figa@gmail.com>
> >>>>>> Cc: Mike Turquette <mturquette@linaro.org>
> >>>>>> Cc: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
> >>>>>> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> >>>>>> ---
> >>>>>> drivers/clk/clk.c | 3 +++
> >>>>>> include/linux/clk-provider.h | 1 +
> >>>>>> 2 files changed, 4 insertions(+)
> >>>>>>
> >>>>>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> >>>>>> index f85c8e2..97cc73e 100644
> >>>>>> --- a/drivers/clk/clk.c
> >>>>>> +++ b/drivers/clk/clk.c
> >>>>>> @@ -1771,6 +1771,9 @@ static void clk_change_rate(struct clk_core *clk)
> >>>>>> if (clk->notifier_count && old_rate != clk->rate)
> >>>>>> __clk_notify(clk, POST_RATE_CHANGE, old_rate, clk->rate);
> >>>>>>
> >>>>>> + if (clk->flags & CLK_RECALC_NEW_RATES)
> >>>>>> + (void)clk_calc_new_rates(clk, clk->new_rate);
> >>>>>> +
> >>>>>> /*
> >>>>>> * Use safe iteration, as change_rate can actually swap parents
> >>>>>> * for certain clock types.
> >>>>>> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> >>>>>> index 28abf1b..8d1aebe 100644
> >>>>>> --- a/include/linux/clk-provider.h
> >>>>>> +++ b/include/linux/clk-provider.h
> >>>>>> @@ -31,6 +31,7 @@
> >>>>>> #define CLK_GET_RATE_NOCACHE BIT(6) /* do not use the cached clk rate */
> >>>>>> #define CLK_SET_RATE_NO_REPARENT BIT(7) /* don't re-parent on rate change */
> >>>>>> #define CLK_GET_ACCURACY_NOCACHE BIT(8) /* do not use the cached clk accuracy */
> >>>>>> +#define CLK_RECALC_NEW_RATES BIT(9) /* recalc rates after notifications */
> >>>>>
> >>>>> Mike, Stephen, what do you think about this? I'm rather resistant to
> >>>>> this new flag approach, it looks like a hack. I don't seem to have better
> >>>>> ideas to address the missing rate recalculation issue though.
> >>>>
> >>>> I also do not like it. The root of the problem is the use of clk
> >>>> notifiers to change clk rates. This is also a hack and it points towards
> >>>> some missing infrastructure in the clock framework.
> >>>
> >>> I'm very surprised by this. Clock changes using clock notifiers in
> >>> Thomas' original patchset were Acked by you:
> >>>
> >>> "[PATCH v12 1/6] clk: samsung: add infrastructure to register cpu clocks"
> >>> https://www.marc.info/?l=linux-arm-kernel&m=141657613203808&w=2
> >>>
> >>> I've only fixed issues present within the original code (this 4 lines
> >>> workaround/hack change to clock subsystem is a result of this), I have
> >>> not changed it fundamentally.
> >>
> >> Moreover similar changes for rockchip SoCs (which were explicitly based
> >> on Thomas' patches as noted in the code!) have already been merged in
> >> 3.18:
> >>
> >> http://lkml.iu.edu/hypermail/linux/kernel/1410.1/02644.html
> >>
> >> and are available in commit f6fba5f6967dbc062a7c138d67e2314220f5dd04
> >> ("clk: rockchip: add new clock-type for the cpuclk").
> >>
> >> I understand that my findings have uncovered some clock subsystem
> >> deficiencies which resulted in afterthought about fundamental design
> >> of cpu clocks but I have a feeling that our patches are now being
> >> unjustly punished for making these issues public.
> >>
> >> I agree that current patches are not perfect (especially this patch)
> >> but they are good enough IMO. Please also understand that there were
> >> some serious work put into validating and reviewing them.
> >
> > You know what? You're right.
> >
> > I don't really like this cpu-clock code (and similarly I don't like
> > Tegra's EMC code which requires access to clk_hw_reparent). But I slept
> > on this issue overnight and it doesn't seem right for me to hold back
> > these patches when the better solution is currently vaporware (I have
> > some code but it's far from ready).
> >
> > It occurs to me that the best decision I can take is to merge it now and
> > then force you guys to switch over when the new infrastructure is
> > available. That is more reasonable than delaying the patches getting
> > pulled.
> >
> > So how to merge it? Viresh has given his Ack and is OK for the cpufreq
> > changes to go through another tree. I can take the whole thing with
> > Kukjin's Ack on the ARM dts patch, or we can set up an immutable
> > branch.
>
> I already acked the DTS [0] patch and I'm fine with it. However there
> would be some conflicts if this went through tree different than
> Samsung. There are many Exynos4 DTS changes in the queue for 4.2.
>
> Are there any objections for picking the DTS patch to Samsung tree?

That's fine with me. I don't foresee any build problems if I take
patches 1-3 and 5-6. So I'll take those and you'll take #4, sound good?

Regards,
Mike

>
> Best regards,
> Krzysztof
>
> [0] https://lkml.org/lkml/2015/5/7/999
>
> >
> > If you really want to make my life easy you can send a pull request for
> > these patches (and the other Exynos cpufreq/cpu-clock series).
> >
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