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

[Mike Turquette <mturquette@linaro.org>]

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.

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?

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
>