Re: [PATCH v4 5/8] clk: exynos: use cpu-clock provider type to represent arm clock.

[Lukasz Majewski <l.majewski@samsung.com>]

Hi Thomas,

> On Thu, May 15, 2014 at 3:07 AM, Mike Turquette
> <mturquette@linaro.org> wrote:
> > Quoting Thomas Abraham (2014-05-13 18:11:13)
> >> From: Thomas Abraham <thomas.ab@samsung.com>
> >>
> >> With the addition of the new Samsung specific cpu-clock type, the
> >> arm clock can be represented as a cpu-clock type and the
> >> independent clock blocks that made up the arm clock can be removed.
> >
> > <rant>
> >
> > I am not a fan of this type of "clock hiding". Certainly the design
> > of the CCF allows for a clock provider to obfuscate it's internals;
> > there was never a requirement that every clock node be exposed to
> > Linux as a struct clk. A truly obfuscated system could only expose
> > leaf clocks that are consumed by Linux device drivers, and never
> > expose any of the intermediary clocks in between the input clock
> > signal (if it exists) and the leaf nodes.
> >
> > However I feel that this patch is more of a workaround to the fact
> > that the clock framework today does not make DVFS transitions (or
> > coordinated, multi-clock rate change transitions) easy to control.
> > The generic "walk up the tree" algorithm might give you the right
> > rate, but perhaps using a non-validated combination of PLL
> > frequency and adjustable-rate dividers, or a combination that his
> > higher jitter or is more likely to unlock at higher temperatures,
> > etc.
> >
> > Back in the pre-CCF days lots of folks implemented this with
> > "virtual" clock nodes that simply called "clk_set_rate" or whatever
> > on the affected clocks, or even worse just banged a bunch of
> > registers.
> >
> > The cbus clock series for Tegra is also looks a little like this.
> >
> > </rant>
> >
> > Thomas,
> >
> > Would a coordinated clock rate change method solve this problem for
> > you in place of the cpu-clock provider type? A poorly conceived
> > call graph for this might look something like:
> >
> > clk_set_rate(div_arm2, 1000000);
> > -> if (div_arm2->coordinated == true)
> >         clk_coordinate_rates(div_arm2, 1000000);
> >         -> clk->ops->coordinate(div_arm2->hw, 1000000);
> >            -> vendor_supplied_magic()
> >
> > The vendor_supplied_magic() would be a callback that essentially
> > calls clk_set_rate() on all of the affected (coordinated) clocks.
> > In your case that looks like mout_core, div_core, div_core2,
> > arm_clk and sclk_apll for Exynos4.

I might misinterpret the idea here, but is clk_set_rate() function
ready to handle atomic change for several clocks? Especially setting
rate of dividers located in the same register, represented as different
clocks to CCF.

As fair as I remember it was not possible to serialize operations on
clocks with calling clk_set_rate() several times. Those had to be done
instantly, otherwise platform hanged.

Am I missing something, or a major improvement had I overlooked?

> >
> > The trick is that calling clk_set_rate() from any driver would
> > initiate this coordinated rate change, and then the exynos clock
> > driver would set up the coordinated clocks itself. No new API is
> > introduced to drivers (since it still uses clk_set_rate) and now a
> > new clock provider doesn't have to be invented every time we have a
> > couple of clocks involved in a DVFS transition.
> >
> > Does this sound right to you or have I horribly misinterpreted the
> > point of these clock patches?
> 
> Mike,
> 
> Thanks for your comments. If I have understood the coordinated clock
> as described above, I believe this patch series also attempts to do
> almost the same thing. The advantage of using coordinated clock over
> the approach in this series is that each platform need not define a
> new clock type.
> 
> In this patch series, for all exynos SoC's, a new cpu clock type was
> introduced which is reusable for multi-cluster exynos SoCs as well.
> The new clock type is part of the clock driver and all drivers can use
> standard clock API to access this clock type instance.
> 
> So probably, all the logic for the new cpu_clk clock type introduced
> in this patch would go into the vendor_supplied_magic() callback. So
> it sounds like the coordinated clock approach would be helpful. Is
> this something that you are already working on?
> 
> Thanks,
> Thomas.
> 
> >
> > Thanks,
> > Mike
> >
> >>
> >> Cc: Tomasz Figa <t.figa@samsung.com>
> >> Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
> >> ---
> >>  drivers/clk/samsung/clk-exynos4.c      |   25
> >> +++++++++---------------- drivers/clk/samsung/clk-exynos5250.c
> >> |   12 ++++++------ include/dt-bindings/clock/exynos5250.h |    1 +
> >>  3 files changed, 16 insertions(+), 22 deletions(-)
> >>
> >> diff --git a/drivers/clk/samsung/clk-exynos4.c
> >> b/drivers/clk/samsung/clk-exynos4.c index b4f9672..7e3bb16c 100644
> >> --- a/drivers/clk/samsung/clk-exynos4.c
> >> +++ b/drivers/clk/samsung/clk-exynos4.c
> >> @@ -471,7 +471,6 @@ static struct samsung_mux_clock
> >> exynos4210_mux_clks[] __initdata = { MUX(0, "mout_fimd1",
> >> group1_p4210, E4210_SRC_LCD1, 0, 4), MUX(0, "mout_mipi1",
> >> group1_p4210, E4210_SRC_LCD1, 12, 4), MUX(CLK_SCLK_MPLL,
> >> "sclk_mpll", mout_mpll_p, SRC_CPU, 8, 1),
> >> -       MUX(CLK_MOUT_CORE, "mout_core", mout_core_p4210, SRC_CPU,
> >> 16, 1), MUX(CLK_SCLK_VPLL, "sclk_vpll", sclk_vpll_p4210, SRC_TOP0,
> >> 8, 1), MUX(CLK_MOUT_FIMC0, "mout_fimc0", group1_p4210, SRC_CAM, 0,
> >> 4), MUX(CLK_MOUT_FIMC1, "mout_fimc1", group1_p4210, SRC_CAM, 4, 4),
> >> @@ -530,7 +529,6 @@ static struct samsung_mux_clock
> >> exynos4x12_mux_clks[] __initdata = { MUX(0, "mout_jpeg",
> >> mout_jpeg_p, E4X12_SRC_CAM1, 8, 1), MUX(CLK_SCLK_MPLL,
> >> "sclk_mpll", mout_mpll_p, SRC_DMC, 12, 1), MUX(CLK_SCLK_VPLL,
> >> "sclk_vpll", mout_vpll_p, SRC_TOP0, 8, 1),
> >> -       MUX(CLK_MOUT_CORE, "mout_core", mout_core_p4x12, SRC_CPU,
> >> 16, 1), MUX(CLK_MOUT_FIMC0, "mout_fimc0", group1_p4x12, SRC_CAM,
> >> 0, 4), MUX(CLK_MOUT_FIMC1, "mout_fimc1", group1_p4x12, SRC_CAM, 4,
> >> 4), MUX(CLK_MOUT_FIMC2, "mout_fimc2", group1_p4x12, SRC_CAM, 8, 4),
> >> @@ -572,8 +570,6 @@ static struct samsung_mux_clock
> >> exynos4x12_mux_clks[] __initdata = {
> >>
> >>  /* list of divider clocks supported in all exynos4 soc's */
> >>  static struct samsung_div_clock exynos4_div_clks[] __initdata = {
> >> -       DIV(0, "div_core", "mout_core", DIV_CPU0, 0, 3),
> >> -       DIV(0, "div_core2", "div_core", DIV_CPU0, 28, 3),
> >>         DIV(0, "div_fimc0", "mout_fimc0", DIV_CAM, 0, 4),
> >>         DIV(0, "div_fimc1", "mout_fimc1", DIV_CAM, 4, 4),
> >>         DIV(0, "div_fimc2", "mout_fimc2", DIV_CAM, 8, 4),
> >> @@ -619,8 +615,8 @@ static struct samsung_div_clock
> >> exynos4_div_clks[] __initdata = { DIV(0, "div_spi_pre2",
> >> "div_spi2", DIV_PERIL2, 8, 8), DIV(0, "div_audio1", "mout_audio1",
> >> DIV_PERIL4, 0, 4), DIV(0, "div_audio2", "mout_audio2", DIV_PERIL4,
> >> 16, 4),
> >> -       DIV(CLK_ARM_CLK, "arm_clk", "div_core2", DIV_CPU0, 28, 3),
> >> -       DIV(CLK_SCLK_APLL, "sclk_apll", "mout_apll", DIV_CPU0, 24,
> >> 3),
> >> +       DIV_F(CLK_SCLK_APLL, "sclk_apll", "mout_apll", DIV_CPU0,
> >> 24, 3,
> >> +                       CLK_GET_RATE_NOCACHE, 0),
> >>         DIV_F(0, "div_mipi_pre0", "div_mipi0", DIV_LCD0, 20, 4,
> >>                         CLK_SET_RATE_PARENT, 0),
> >>         DIV_F(0, "div_mmc_pre0", "div_mmc0", DIV_FSYS1, 8, 8,
> >> @@ -1003,12 +999,6 @@ static struct samsung_gate_clock
> >> exynos4x12_gate_clks[] __initdata = { 0),
> >>  };
> >>
> >> -static struct samsung_clock_alias exynos4_aliases[] __initdata = {
> >> -       ALIAS(CLK_MOUT_CORE, NULL, "moutcore"),
> >> -       ALIAS(CLK_ARM_CLK, NULL, "armclk"),
> >> -       ALIAS(CLK_SCLK_APLL, NULL, "mout_apll"),
> >> -};
> >> -
> >>  static struct samsung_clock_alias exynos4210_aliases[] __initdata
> >> = { ALIAS(CLK_SCLK_MPLL, NULL, "mout_mpll"),
> >>  };
> >> @@ -1241,6 +1231,9 @@ static void __init exynos4_clk_init(struct
> >> device_node *np, ARRAY_SIZE(exynos4210_gate_clks));
> >>                 samsung_clk_register_alias(exynos4210_aliases,
> >>                         ARRAY_SIZE(exynos4210_aliases));
> >> +               exynos_register_arm_clock(CLK_ARM_CLK,
> >> mout_core_p4210,
> >> +                       ARRAY_SIZE(mout_core_p4210), reg_base, np,
> >> NULL,
> >> +                       &samsung_clk_lock);
> >>         } else {
> >>                 samsung_clk_register_mux(exynos4x12_mux_clks,
> >>                         ARRAY_SIZE(exynos4x12_mux_clks));
> >> @@ -1250,11 +1243,11 @@ static void __init exynos4_clk_init(struct
> >> device_node *np, ARRAY_SIZE(exynos4x12_gate_clks));
> >>                 samsung_clk_register_alias(exynos4x12_aliases,
> >>                         ARRAY_SIZE(exynos4x12_aliases));
> >> +               exynos_register_arm_clock(CLK_ARM_CLK,
> >> mout_core_p4x12,
> >> +                       ARRAY_SIZE(mout_core_p4x12), reg_base, np,
> >> NULL,
> >> +                       &samsung_clk_lock);
> >>         }
> >>
> >> -       samsung_clk_register_alias(exynos4_aliases,
> >> -                       ARRAY_SIZE(exynos4_aliases));
> >> -
> >>         exynos4_clk_sleep_init();
> >>
> >>         pr_info("%s clocks: sclk_apll = %ld, sclk_mpll = %ld\n"
> >> @@ -1262,7 +1255,7 @@ static void __init exynos4_clk_init(struct
> >> device_node *np, exynos4_soc == EXYNOS4210 ? "Exynos4210" :
> >> "Exynos4x12", _get_rate("sclk_apll"), _get_rate("sclk_mpll"),
> >>                 _get_rate("sclk_epll"), _get_rate("sclk_vpll"),
> >> -               _get_rate("arm_clk"));
> >> +               _get_rate("armclk"));
> >>  }
> >>
> >>
> >> diff --git a/drivers/clk/samsung/clk-exynos5250.c
> >> b/drivers/clk/samsung/clk-exynos5250.c index e7ee442..3fe1ca0
> >> 100644 --- a/drivers/clk/samsung/clk-exynos5250.c
> >> +++ b/drivers/clk/samsung/clk-exynos5250.c
> >> @@ -260,8 +260,6 @@ static struct samsung_mux_clock
> >> exynos5250_mux_clks[] __initdata = { */
> >>         MUX_FA(0, "mout_apll", mout_apll_p, SRC_CPU, 0, 1,
> >>                                         CLK_SET_RATE_PARENT, 0,
> >> "mout_apll"),
> >> -       MUX_A(0, "mout_cpu", mout_cpu_p, SRC_CPU, 16, 1,
> >> "mout_cpu"), -
> >>         /*
> >>          * CMU_CORE
> >>          */
> >> @@ -339,9 +337,8 @@ static struct samsung_div_clock
> >> exynos5250_div_clks[] __initdata = { /*
> >>          * CMU_CPU
> >>          */
> >> -       DIV(0, "div_arm", "mout_cpu", DIV_CPU0, 0, 3),
> >> -       DIV(0, "div_apll", "mout_apll", DIV_CPU0, 24, 3),
> >> -       DIV_A(0, "div_arm2", "div_arm", DIV_CPU0, 28, 3, "armclk"),
> >> +       DIV_F(0, "div_apll", "mout_apll", DIV_CPU0, 24, 3,
> >> +                       CLK_GET_RATE_NOCACHE, 0),
> >>
> >>         /*
> >>          * CMU_TOP
> >> @@ -721,10 +718,13 @@ static void __init
> >> exynos5250_clk_init(struct device_node *np)
> >> ARRAY_SIZE(exynos5250_div_clks));
> >> samsung_clk_register_gate(exynos5250_gate_clks,
> >> ARRAY_SIZE(exynos5250_gate_clks));
> >> +       exynos_register_arm_clock(CLK_ARM_CLK, mout_cpu_p,
> >> +                       ARRAY_SIZE(mout_cpu_p), reg_base, np, NULL,
> >> +                       &samsung_clk_lock);
> >>
> >>         exynos5250_clk_sleep_init();
> >>
> >>         pr_info("Exynos5250: clock setup completed, armclk=%ld\n",
> >> -                       _get_rate("div_arm2"));
> >> +                       _get_rate("armclk"));
> >>  }
> >>  CLK_OF_DECLARE(exynos5250_clk, "samsung,exynos5250-clock",
> >> exynos5250_clk_init); diff --git
> >> a/include/dt-bindings/clock/exynos5250.h
> >> b/include/dt-bindings/clock/exynos5250.h index 922f2dc..59a10fb
> >> 100644 --- a/include/dt-bindings/clock/exynos5250.h +++
> >> b/include/dt-bindings/clock/exynos5250.h @@ -21,6 +21,7 @@
> >>  #define CLK_FOUT_CPLL          6
> >>  #define CLK_FOUT_EPLL          7
> >>  #define CLK_FOUT_VPLL          8
> >> +#define CLK_ARM_CLK            12
> >>
> >>  /* gate for special clocks (sclk) */
> >>  #define CLK_SCLK_CAM_BAYER     128
> >> --
> >> 1.7.4.4
> >>
> 
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-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group