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Date:	Thu, 24 Jul 2014 08:42:24 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	Tomasz Figa <t.figa@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v2 1/2] clk: samsung: exynos4: Enable ARMCLK down feature

On śro, 2014-07-23 at 17:18 -0700, Mike Turquette wrote:
> Quoting Krzysztof Kozlowski (2014-07-18 07:36:32)
> > Enable ARMCLK down feature on all Exynos4 SoCs. The frequency of
> > ARMCLK will be reduced upon entering idle mode (WFI or WFE).
> > 
> > The feature behaves like very fast cpufreq ondemand governor. In idle
> > mode this reduces energy consumption on full frequency chosen by
> > cpufreq governor by approximately:
> >  - Trats2:  6.5% (153 mA -> 143 mA)
> >  - Trats:  33.0% (180 mA -> 120 mA)
> >  - Gear1:  27.0% (180 mA -> 130 mA)
> 
> Nice power savings! Just a quick question on this feature: the clock
> frequency is changed in hardware as a result of WFI/WFE?

Yes. This feature makes changes in DIVCORE and DIVCORE2 clock dividers
when given core enters WFI/WFE.

> And this only
> happens when all CPUs in a cluster (e.g. all 4 CPUs in Exynos 4412) are
> in WFI/WFE state?

No, this is per-core. However measured energy savings above were in case
where all cores entered idle (WFI).

Best regards,
Krzysztof


> 
> Thanks,
> Mike
> 
> > 
> > The patch uses simillar settings as Exynos5250 (clk-exynos5250.c),
> > except it disables clock up feature and on Exynos4412 ARMCLK down is
> > enabled for all 4 cores.
> > 
> > Tested on Trats board (Exynos4210), Trats2 board (Exynos4412) and
> > Samsung Gear 1 (Exynos4212).
> > 
> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> > 
> > ---
> > 
> > Changes since v1:
> > 1. Add PWR_CTRL registers to the list of saved clk registers on
> >    Exynos4x12. Suggested by Tomasz Figa.
> > 2. Disable the clock up feature. (sug. Tomasz Figa)
> > 3. Use macros for setting clock down ratio. (sug. Tomasz Figa)
> > 4. Use num_possible_cpus() for exception on Exynos4x12. (sug. Tomasz
> >    Figa)
> > 5. Enable the clock down feature also on Exynos4210 Trats board.
> > ---
> >  drivers/clk/samsung/clk-exynos4.c | 46 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 46 insertions(+)
> > 
> > diff --git a/drivers/clk/samsung/clk-exynos4.c b/drivers/clk/samsung/clk-exynos4.c
> > index 7f4a473a7ad7..86c7709dc6d6 100644
> > --- a/drivers/clk/samsung/clk-exynos4.c
> > +++ b/drivers/clk/samsung/clk-exynos4.c
> > @@ -114,11 +114,27 @@
> >  #define DIV_CPU1               0x14504
> >  #define GATE_SCLK_CPU          0x14800
> >  #define GATE_IP_CPU            0x14900
> > +#define PWR_CTRL1              0x15020
> > +#define E4X12_PWR_CTRL2                0x15024
> >  #define E4X12_DIV_ISP0         0x18300
> >  #define E4X12_DIV_ISP1         0x18304
> >  #define E4X12_GATE_ISP0                0x18800
> >  #define E4X12_GATE_ISP1                0x18804
> >  
> > +/* Below definitions are used for PWR_CTRL settings */
> > +#define PWR_CTRL1_CORE2_DOWN_RATIO(x)          (((x) & 0x7) << 28)
> > +#define PWR_CTRL1_CORE1_DOWN_RATIO(x)          (((x) & 0x7) << 16)
> > +#define PWR_CTRL1_DIV2_DOWN_EN                 (1 << 9)
> > +#define PWR_CTRL1_DIV1_DOWN_EN                 (1 << 8)
> > +#define PWR_CTRL1_USE_CORE3_WFE                        (1 << 7)
> > +#define PWR_CTRL1_USE_CORE2_WFE                        (1 << 6)
> > +#define PWR_CTRL1_USE_CORE1_WFE                        (1 << 5)
> > +#define PWR_CTRL1_USE_CORE0_WFE                        (1 << 4)
> > +#define PWR_CTRL1_USE_CORE3_WFI                        (1 << 3)
> > +#define PWR_CTRL1_USE_CORE2_WFI                        (1 << 2)
> > +#define PWR_CTRL1_USE_CORE1_WFI                        (1 << 1)
> > +#define PWR_CTRL1_USE_CORE0_WFI                        (1 << 0)
> > +
> >  /* the exynos4 soc type */
> >  enum exynos4_soc {
> >         EXYNOS4210,
> > @@ -155,6 +171,7 @@ static unsigned long exynos4210_clk_save[] __initdata = {
> >         E4210_GATE_IP_LCD1,
> >         E4210_GATE_IP_PERIR,
> >         E4210_MPLL_CON0,
> > +       PWR_CTRL1,
> >  };
> >  
> >  static unsigned long exynos4x12_clk_save[] __initdata = {
> > @@ -164,6 +181,8 @@ static unsigned long exynos4x12_clk_save[] __initdata = {
> >         E4X12_DIV_ISP,
> >         E4X12_DIV_CAM1,
> >         E4X12_MPLL_CON0,
> > +       PWR_CTRL1,
> > +       E4X12_PWR_CTRL2,
> >  };
> >  
> >  static unsigned long exynos4_clk_pll_regs[] __initdata = {
> > @@ -1164,6 +1183,32 @@ static struct samsung_pll_clock exynos4x12_plls[nr_plls] __initdata = {
> >                         VPLL_LOCK, VPLL_CON0, NULL),
> >  };
> >  
> > +static void __init exynos4_core_down_clock(enum exynos4_soc soc)
> > +{
> > +       unsigned int tmp;
> > +
> > +       /*
> > +        * Enable arm clock down (in idle) and set arm divider
> > +        * ratios in WFI/WFE state.
> > +        */
> > +       tmp = (PWR_CTRL1_CORE2_DOWN_RATIO(7) | PWR_CTRL1_CORE1_DOWN_RATIO(7) |
> > +               PWR_CTRL1_DIV2_DOWN_EN | PWR_CTRL1_DIV1_DOWN_EN |
> > +               PWR_CTRL1_USE_CORE1_WFE | PWR_CTRL1_USE_CORE0_WFE |
> > +               PWR_CTRL1_USE_CORE1_WFI | PWR_CTRL1_USE_CORE0_WFI);
> > +       /* On Exynos4412 enable it also on core 2 and 3 */
> > +       if (num_possible_cpus() == 4)
> > +               tmp |= PWR_CTRL1_USE_CORE3_WFE | PWR_CTRL1_USE_CORE2_WFE |
> > +                      PWR_CTRL1_USE_CORE3_WFI | PWR_CTRL1_USE_CORE2_WFI;
> > +       __raw_writel(tmp, reg_base + PWR_CTRL1);
> > +
> > +       /*
> > +        * Disable the clock up feature on Exynos4x12, in case it was
> > +        * enabled by bootloader.
> > +        */
> > +       if (exynos4_soc == EXYNOS4X12)
> > +               __raw_writel(0x0, reg_base + E4X12_PWR_CTRL2);
> > +}
> > +
> >  /* register exynos4 clocks */
> >  static void __init exynos4_clk_init(struct device_node *np,
> >                                     enum exynos4_soc soc)
> > @@ -1250,6 +1295,7 @@ static void __init exynos4_clk_init(struct device_node *np,
> >         samsung_clk_register_alias(ctx, exynos4_aliases,
> >                         ARRAY_SIZE(exynos4_aliases));
> >  
> > +       exynos4_core_down_clock(soc);
> >         exynos4_clk_sleep_init();
> >  
> >         pr_info("%s clocks: sclk_apll = %ld, sclk_mpll = %ld\n"
> > -- 
> > 1.9.1
> > 

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