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@xxxxxxxxxxx>
Cc: Tomasz Figa <tomasz.figa@xxxxxxxxx>
Cc: Mike Turquette <mturquette@xxxxxxxxxx>
Cc: Javier Martinez Canillas <javier.martinez@xxxxxxxxxxxxxxx>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
---
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 */
struct clk_hw;
struct clk_core;
--
1.7.9.5
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