Re: [PATCH v3 7/7] clk: meson: a1: add Amlogic A1 CPU clock controller driver

Jerome Brunet
2024-06-10T10:06:33Z

On Wed 15 May 2024 at 21:47, Dmitry Rokosov <ddrokosov@salutedevices.com> wrote:

> The CPU clock controller plays a general role in the Amlogic A1 SoC
> family by generating CPU clocks. As an APB slave module, it offers the
> capability to inherit the CPU clock from two sources: the internal fixed
> clock known as 'cpu fixed clock' and the external input provided by the
> A1 PLL clock controller, referred to as 'syspll'.
>
> It is important for the driver to handle cpu_clk rate switching
> effectively by transitioning to the CPU fixed clock to avoid any
> potential execution freezes.
>
> Signed-off-by: Dmitry Rokosov <ddrokosov@salutedevices.com>
> ---
> drivers/clk/meson/Kconfig | 10 ++
> drivers/clk/meson/Makefile | 1 +
> drivers/clk/meson/a1-cpu.c | 331 +++++++++++++++++++++++++++++++++++++
> 3 files changed, 342 insertions(+)
> create mode 100644 drivers/clk/meson/a1-cpu.c
>
> diff --git a/drivers/clk/meson/Kconfig b/drivers/clk/meson/Kconfig
> index 80c4a18c83d2..148d4495eee3 100644
> --- a/drivers/clk/meson/Kconfig
> +++ b/drivers/clk/meson/Kconfig
> @@ -111,6 +111,16 @@ config COMMON_CLK_AXG_AUDIO
> Support for the audio clock controller on AmLogic A113D devices,
> aka axg, Say Y if you want audio subsystem to work.
>
> +config COMMON_CLK_A1_CPU
> + tristate "Amlogic A1 SoC CPU controller support"
> + depends on ARM64
> + select COMMON_CLK_MESON_REGMAP
> + select COMMON_CLK_MESON_CLKC_UTILS
> + help
> + Support for the CPU clock controller on Amlogic A113L based
> + device, A1 SoC Family. Say Y if you want A1 CPU clock controller
> + to work.
> +
> config COMMON_CLK_A1_PLL
> tristate "Amlogic A1 SoC PLL controller support"
> depends on ARM64
> diff --git a/drivers/clk/meson/Makefile b/drivers/clk/meson/Makefile
> index 4968fc7ad555..2a06eb0303d6 100644
> --- a/drivers/clk/meson/Makefile
> +++ b/drivers/clk/meson/Makefile
> @@ -18,6 +18,7 @@ obj-$(CONFIG_COMMON_CLK_MESON_AUDIO_RSTC) += meson-audio-rstc.o
>
> obj-$(CONFIG_COMMON_CLK_AXG) += axg.o axg-aoclk.o
> obj-$(CONFIG_COMMON_CLK_AXG_AUDIO) += axg-audio.o
> +obj-$(CONFIG_COMMON_CLK_A1_CPU) += a1-cpu.o
> obj-$(CONFIG_COMMON_CLK_A1_PLL) += a1-pll.o
> obj-$(CONFIG_COMMON_CLK_A1_PERIPHERALS) += a1-peripherals.o
> obj-$(CONFIG_COMMON_CLK_A1_AUDIO) += a1-audio.o
> diff --git a/drivers/clk/meson/a1-cpu.c b/drivers/clk/meson/a1-cpu.c
> new file mode 100644
> index 000000000000..a9edabeafea9
> --- /dev/null
> +++ b/drivers/clk/meson/a1-cpu.c
> @@ -0,0 +1,331 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Amlogic A1 SoC family CPU Clock Controller driver.
> + *
> + * Copyright (c) 2024, SaluteDevices. All Rights Reserved.
> + * Author: Dmitry Rokosov <ddrokosov@salutedevices.com>
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/clk-provider.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/platform_device.h>
> +#include "clk-regmap.h"
> +#include "meson-clkc-utils.h"
> +
> +#include <dt-bindings/clock/amlogic,a1-cpu-clkc.h>
> +
> +/* CPU Clock Controller register offset */
> +#define CPUCTRL_CLK_CTRL0 0x0
> +#define CPUCTRL_CLK_CTRL1 0x4
> +
> +static u32 cpu_fsource_sel_table[] = { 0, 1, 2 };
> +static const struct clk_parent_data cpu_fsource_sel_parents[] = {
> + { .fw_name = "xtal" },
> + { .fw_name = "fclk_div2" },
> + { .fw_name = "fclk_div3" },
> +};
> +
> +static struct clk_regmap cpu_fsource_sel0 = {
> + .data = &(struct clk_regmap_mux_data) {
> + .offset = CPUCTRL_CLK_CTRL0,
> + .mask = 0x3,
> + .shift = 0,
> + .table = cpu_fsource_sel_table,
> + },
> + .hw.init = &(struct clk_init_data) {
> + .name = "cpu_fsource_sel0",
> + .ops = &clk_regmap_mux_ops,
> + .parent_data = cpu_fsource_sel_parents,
> + .num_parents = ARRAY_SIZE(cpu_fsource_sel_parents),
> + .flags = CLK_SET_RATE_PARENT,

I don't think setting the rates of controller parents is appropriate

> + },
> +};
> +
> +static struct clk_regmap cpu_fsource_div0 = {
> + .data = &(struct clk_regmap_div_data) {
> + .offset = CPUCTRL_CLK_CTRL0,
> + .shift = 4,
> + .width = 6,
> + },
> + .hw.init = &(struct clk_init_data) {
> + .name = "cpu_fsource_div0",
> + .ops = &clk_regmap_divider_ops,
> + .parent_hws = (const struct clk_hw *[]) {
> + &cpu_fsource_sel0.hw
> + },
> + .num_parents = 1,
> + .flags = CLK_SET_RATE_PARENT,
> + },
> +};
> +
> +static struct clk_regmap cpu_fsel0 = {
> + .data = &(struct clk_regmap_mux_data) {
> + .offset = CPUCTRL_CLK_CTRL0,
> + .mask = 0x1,
> + .shift = 2,
> + },
> + .hw.init = &(struct clk_init_data) {
> + .name = "cpu_fsel0",
> + .ops = &clk_regmap_mux_ops,
> + .parent_hws = (const struct clk_hw *[]) {
> + &cpu_fsource_sel0.hw,
> + &cpu_fsource_div0.hw,
> + },
> + .num_parents = 2,
> + .flags = CLK_SET_RATE_GATE | CLK_SET_RATE_PARENT,
> + },
> +};
> +
> +static struct clk_regmap cpu_fsource_sel1 = {
> + .data = &(struct clk_regmap_mux_data) {
> + .offset = CPUCTRL_CLK_CTRL0,
> + .mask = 0x3,
> + .shift = 16,
> + .table = cpu_fsource_sel_table,
> + },
> + .hw.init = &(struct clk_init_data) {
> + .name = "cpu_fsource_sel1",
> + .ops = &clk_regmap_mux_ops,
> + .parent_data = cpu_fsource_sel_parents,
> + .num_parents = ARRAY_SIZE(cpu_fsource_sel_parents),
> + .flags = CLK_SET_RATE_PARENT,
> + },
> +};
> +
> +static struct clk_regmap cpu_fsource_div1 = {
> + .data = &(struct clk_regmap_div_data) {
> + .offset = CPUCTRL_CLK_CTRL0,
> + .shift = 20,
> + .width = 6,
> + },
> + .hw.init = &(struct clk_init_data) {
> + .name = "cpu_fsource_div1",
> + .ops = &clk_regmap_divider_ops,
> + .parent_hws = (const struct clk_hw *[]) {
> + &cpu_fsource_sel1.hw
> + },
> + .num_parents = 1,
> + .flags = CLK_SET_RATE_PARENT,
> + },
> +};
> +
> +static struct clk_regmap cpu_fsel1 = {
> + .data = &(struct clk_regmap_mux_data) {
> + .offset = CPUCTRL_CLK_CTRL0,
> + .mask = 0x1,
> + .shift = 18,
> + },
> + .hw.init = &(struct clk_init_data) {
> + .name = "cpu_fsel1",
> + .ops = &clk_regmap_mux_ops,
> + .parent_hws = (const struct clk_hw *[]) {
> + &cpu_fsource_sel1.hw,
> + &cpu_fsource_div1.hw,
> + },
> + .num_parents = 2,
> + .flags = CLK_SET_RATE_GATE | CLK_SET_RATE_PARENT,
> + },
> +};
> +
> +static struct clk_regmap cpu_fclk = {
> + .data = &(struct clk_regmap_mux_data) {
> + .offset = CPUCTRL_CLK_CTRL0,
> + .mask = 0x1,
> + .shift = 10,
> + },
> + .hw.init = &(struct clk_init_data) {
> + .name = "cpu_fclk",
> + .ops = &clk_regmap_mux_ops,
> + .parent_hws = (const struct clk_hw *[]) {
> + &cpu_fsel0.hw,
> + &cpu_fsel1.hw,
> + },
> + .num_parents = 2,
> + .flags = CLK_SET_RATE_PARENT,
> + },
> +};
> +
> +static struct clk_regmap cpu_clk = {
> + .data = &(struct clk_regmap_mux_data) {
> + .offset = CPUCTRL_CLK_CTRL0,
> + .mask = 0x1,
> + .shift = 11,
> + },
> + .hw.init = &(struct clk_init_data) {
> + .name = "cpu_clk",
> + .ops = &clk_regmap_mux_ops,
> + .parent_data = (const struct clk_parent_data []) {
> + { .hw = &cpu_fclk.hw },
> + { .fw_name = "sys_pll", },
> + },

You've put CLK_SET_RATE_GATE on fixed clock path but not the SYS_PLL
... that is odd. IMO there should be a bypass input clock to the sys_pll
with that flag.

> + .num_parents = 2,
> + .flags = CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
> + },
> +};
> +
> +/* Array of all clocks registered by this provider */
> +static struct clk_hw *a1_cpu_hw_clks[] = {
> + [CLKID_CPU_FSOURCE_SEL0] = &cpu_fsource_sel0.hw,
> + [CLKID_CPU_FSOURCE_DIV0] = &cpu_fsource_div0.hw,
> + [CLKID_CPU_FSEL0] = &cpu_fsel0.hw,
> + [CLKID_CPU_FSOURCE_SEL1] = &cpu_fsource_sel1.hw,
> + [CLKID_CPU_FSOURCE_DIV1] = &cpu_fsource_div1.hw,
> + [CLKID_CPU_FSEL1] = &cpu_fsel1.hw,
> + [CLKID_CPU_FCLK] = &cpu_fclk.hw,
> + [CLKID_CPU_CLK] = &cpu_clk.hw,
> +};
> +
> +static struct clk_regmap *const a1_cpu_regmaps[] = {
> + &cpu_fsource_sel0,
> + &cpu_fsource_div0,
> + &cpu_fsel0,
> + &cpu_fsource_sel1,
> + &cpu_fsource_div1,
> + &cpu_fsel1,
> + &cpu_fclk,
> + &cpu_clk,
> +};
> +
> +static struct regmap_config a1_cpu_regmap_cfg = {
> + .reg_bits = 32,
> + .val_bits = 32,
> + .reg_stride = 4,
> + .max_register = CPUCTRL_CLK_CTRL1,
> +};
> +
> +static struct meson_clk_hw_data a1_cpu_clks = {
> + .hws = a1_cpu_hw_clks,
> + .num = ARRAY_SIZE(a1_cpu_hw_clks),
> +};
> +
> +struct a1_sys_pll_nb_data {
> + struct notifier_block nb;
> + struct clk_hw *cpu_clk;
> + struct clk_hw *cpu_fclk;
> + struct clk *sys_pll;
> +};

There are number of things which are wrong with this notifier.

First, and foremost, this is a clock controller driver ... it should not
handle cpufreq policy. There is subsystem for that

> +
> +static int meson_a1_sys_pll_notifier_cb(struct notifier_block *nb,
> + unsigned long event, void *data)
> +{
> + struct a1_sys_pll_nb_data *nbd;
> + int ret = 0;
> +
> + nbd = container_of(nb, struct a1_sys_pll_nb_data, nb);
> +
> + switch (event) {
> + case PRE_RATE_CHANGE:
> + /*
> + * Clock sys_pll will be changed to feed cpu_clk,
> + * configure cpu_clk to use cpu_fclk fixed clock.
> + */
> + ret = clk_hw_set_parent(nbd->cpu_clk, nbd->cpu_fclk);

This jumps to whatever was the last frequency below 768MHz ... that does
not seems deterministic or safe.
> +
> + /* Wait for clock propagation */
> + if (!ret)
> + udelay(100);
> +
> + break;
> +
> + case POST_RATE_CHANGE:
> + /*
> + * Clock sys_pll rate has ben calculated,
> + * switch back cpu_clk to sys_pll
> + */
> + ret = clk_set_parent(nbd->cpu_clk->clk, nbd->sys_pll);

So whenever sys_pll changes, even if was not used by the CPU at that
time, this will change back to the sys_pll. Again, that seems fragile

> +
> + /* Wait for clock propagation */
> + if (!ret)
> + udelay(100);
> + break;
> +
> + default:
> + pr_warn("Unknown event %lu for sys_pll notifier\n", event);
> + break;
> + }
> +
> + return notifier_from_errno(ret);
> +}
> +
> +static struct a1_sys_pll_nb_data a1_sys_pll_nb_data = {
> + .nb.notifier_call = meson_a1_sys_pll_notifier_cb,
> + .cpu_clk = &cpu_clk.hw,
> + .cpu_fclk = &cpu_fclk.hw,
> +};
> +
> +static int meson_a1_dvfs_setup(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct clk *sys_pll;
> + int ret;
> +
> + /* Setup clock notifier for sys_pll clk */
> + sys_pll = devm_clk_get(dev, "sys_pll");
> + if (IS_ERR(sys_pll))
> + return dev_err_probe(dev, PTR_ERR(sys_pll),
> + "can't get sys_pll as notifier clock\n");
> +
> + a1_sys_pll_nb_data.sys_pll = sys_pll;
> + ret = devm_clk_notifier_register(dev, sys_pll,
> + &a1_sys_pll_nb_data.nb);
> + if (ret)
> + return dev_err_probe(dev, ret,
> + "can't register sys_pll notifier\n");
> +
> + return ret;
> +}

I don't think these notifiers are appropriate to handle CPU frequency
change. Cpufreq has a .target_intermediate() callback that seems more
appropriate to switch the CPU to a safe clock while relocking a PLL.

You should have a look at it and probably at the imx-cpufreq-dt.c which
improves on cpufreq-dt.c to handle platform quirks

> +
> +static int meson_a1_cpu_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + void __iomem *base;
> + struct regmap *map;
> + int clkid, i, err;
> +
> + base = devm_platform_ioremap_resource(pdev, 0);
> + if (IS_ERR(base))
> + return dev_err_probe(dev, PTR_ERR(base),
> + "can't ioremap resource\n");
> +
> + map = devm_regmap_init_mmio(dev, base, &a1_cpu_regmap_cfg);
> + if (IS_ERR(map))
> + return dev_err_probe(dev, PTR_ERR(map),
> + "can't init regmap mmio region\n");
> +
> + /* Populate regmap for the regmap backed clocks */
> + for (i = 0; i < ARRAY_SIZE(a1_cpu_regmaps); i++)
> + a1_cpu_regmaps[i]->map = map;
> +
> + for (clkid = 0; clkid < a1_cpu_clks.num; clkid++) {
> + err = devm_clk_hw_register(dev, a1_cpu_clks.hws[clkid]);
> + if (err)
> + return dev_err_probe(dev, err,
> + "clock[%d] registration failed\n",
> + clkid);
> + }
> +
> + err = devm_of_clk_add_hw_provider(dev, meson_clk_hw_get, &a1_cpu_clks);
> + if (err)
> + return dev_err_probe(dev, err, "can't add clk hw provider\n");
> +
> + return meson_a1_dvfs_setup(pdev);
> +}
> +
> +static const struct of_device_id a1_cpu_clkc_match_table[] = {
> + { .compatible = "amlogic,a1-cpu-clkc", },
> + {}
> +};
> +MODULE_DEVICE_TABLE(of, a1_cpu_clkc_match_table);
> +
> +static struct platform_driver a1_cpu_clkc_driver = {
> + .probe = meson_a1_cpu_probe,
> + .driver = {
> + .name = "a1-cpu-clkc",
> + .of_match_table = a1_cpu_clkc_match_table,
> + },
> +};
> +
> +module_platform_driver(a1_cpu_clkc_driver);
> +MODULE_AUTHOR("Dmitry Rokosov <ddrokosov@salutedevices.com>");
> +MODULE_LICENSE("GPL");

--
Jerome