[PATCH v6 4/5] PM / devfreq: Add dynamic scaling for imx8m ddr controller

Leonard Crestez
2019-11-14T18:34:40Z

Add driver for dynamic scaling the DDR Controller on imx8m chips. Actual
frequency switching is implemented inside TF-A, this driver wraps the
SMC calls and synchronizes the clk tree.

The DRAM clocks on imx8m have the following structure (abridged):

+----------+ |\ +------+
| dram_pll |-------|M| dram_core | |
+----------+ |U|---------->| D |
/--|X| | D |
dram_alt_root | |/ | R |
| | C |
+---------+ | |
|FIX DIV/4| | |
+---------+ | |
composite: | | |
+----------+ | | |
| dram_alt |----/ | |
+----------+ | |
| dram_apb |-------------------->| |
+----------+ +------+

The dram_pll is used for higher rates and dram_alt is used for lower
rates. The dram_alt and dram_apb clocks are "imx composite" and their
parent can also be modified.

This driver will prepare/enable the new parents ahead of switching (so
that the expected roots are enabled) and afterwards it will call
clk_set_parent to ensure the parents in clock framework are up-to-date.

The driver relies on dram_pll dram_alt and dram_apb being marked with
CLK_GET_RATE_NOCACHE for rate updates.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
---
drivers/devfreq/Kconfig | 9 +
drivers/devfreq/Makefile | 1 +
drivers/devfreq/imx8m-ddrc.c | 465 +++++++++++++++++++++++++++++++++++
3 files changed, 475 insertions(+)
create mode 100644 drivers/devfreq/imx8m-ddrc.c

diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
index 066e6c4efaa2..923a6132e741 100644
--- a/drivers/devfreq/Kconfig
+++ b/drivers/devfreq/Kconfig
@@ -89,10 +89,19 @@ config ARM_EXYNOS_BUS_DEVFREQ
Each memory bus group could contain many memoby bus block. It reads
PPMU counters of memory controllers by using DEVFREQ-event device
and adjusts the operating frequencies and voltages with OPP support.
This does not yet operate with optimal voltages.

+config ARM_IMX8M_DDRC_DEVFREQ
+ tristate "i.MX8M DDRC DEVFREQ Driver"
+ depends on ARCH_MXC || COMPILE_TEST
+ select DEVFREQ_GOV_SIMPLE_ONDEMAND
+ select DEVFREQ_GOV_USERSPACE
+ help
+ This adds the DEVFREQ driver for the i.MX8M DDR Controller. It allows
+ adjusting DRAM frequency.
+
config ARM_TEGRA_DEVFREQ
tristate "NVIDIA Tegra30/114/124/210 DEVFREQ Driver"
depends on ARCH_TEGRA_3x_SOC || ARCH_TEGRA_114_SOC || \
ARCH_TEGRA_132_SOC || ARCH_TEGRA_124_SOC || \
ARCH_TEGRA_210_SOC || \
diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
index 338ae8440db6..3eb4d5e6635c 100644
--- a/drivers/devfreq/Makefile
+++ b/drivers/devfreq/Makefile
@@ -7,10 +7,11 @@ obj-$(CONFIG_DEVFREQ_GOV_POWERSAVE) += governor_powersave.o
obj-$(CONFIG_DEVFREQ_GOV_USERSPACE) += governor_userspace.o
obj-$(CONFIG_DEVFREQ_GOV_PASSIVE) += governor_passive.o

# DEVFREQ Drivers
obj-$(CONFIG_ARM_EXYNOS_BUS_DEVFREQ) += exynos-bus.o
+obj-$(CONFIG_ARM_IMX8M_DDRC_DEVFREQ) += imx8m-ddrc.o
obj-$(CONFIG_ARM_RK3399_DMC_DEVFREQ) += rk3399_dmc.o
obj-$(CONFIG_ARM_TEGRA_DEVFREQ) += tegra30-devfreq.o
obj-$(CONFIG_ARM_TEGRA20_DEVFREQ) += tegra20-devfreq.o

# DEVFREQ Event Drivers
diff --git a/drivers/devfreq/imx8m-ddrc.c b/drivers/devfreq/imx8m-ddrc.c
new file mode 100644
index 000000000000..fea169619c59
--- /dev/null
+++ b/drivers/devfreq/imx8m-ddrc.c
@@ -0,0 +1,465 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2019 NXP
+ */
+
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/devfreq.h>
+#include <linux/pm_opp.h>
+#include <linux/clk.h>
+#include <linux/clk-provider.h>
+#include <linux/arm-smccc.h>
+
+#define IMX_SIP_DDR_DVFS 0xc2000004
+
+/* Values starting from 0 switch to specific frequency */
+#define IMX_SIP_DDR_FREQ_SET_HIGH 0x00
+
+/* Deprecated after moving IRQ handling to ATF */
+#define IMX_SIP_DDR_DVFS_WAIT_CHANGE 0x0F
+
+/* Query available frequencies. */
+#define IMX_SIP_DDR_DVFS_GET_FREQ_COUNT 0x10
+#define IMX_SIP_DDR_DVFS_GET_FREQ_INFO 0x11
+
+/*
+ * This should be in a 1:1 mapping with devicetree OPPs but
+ * firmware provides additional info.
+ */
+struct imx8m_ddrc_freq {
+ unsigned long rate;
+ unsigned long smcarg;
+ int dram_core_parent_index;
+ int dram_alt_parent_index;
+ int dram_apb_parent_index;
+};
+
+/* Hardware limitation */
+#define IMX8M_DDRC_MAX_FREQ_COUNT 4
+
+/*
+ * i.MX8M DRAM Controller clocks have the following structure (abridged):
+ *
+ * +----------+ |\ +------+
+ * | dram_pll |-------|M| dram_core | |
+ * +----------+ |U|---------->| D |
+ * /--|X| | D |
+ * dram_alt_root | |/ | R |
+ * | | C |
+ * +---------+ | |
+ * |FIX DIV/4| | |
+ * +---------+ | |
+ * composite: | | |
+ * +----------+ | | |
+ * | dram_alt |----/ | |
+ * +----------+ | |
+ * | dram_apb |-------------------->| |
+ * +----------+ +------+
+ *
+ * The dram_pll is used for higher rates and dram_alt is used for lower rates.
+ *
+ * Frequency switching is implemented in TF-A (via SMC call) and can change the
+ * configuration of the clocks, including mux parents. The dram_alt and
+ * dram_apb clocks are "imx composite" and their parent can change too.
+ *
+ * We need to prepare/enable the new mux parents head of switching and update
+ * their information afterwards.
+ */
+struct imx8m_ddrc {
+ struct devfreq_dev_profile profile;
+ struct devfreq *devfreq;
+
+ /* For frequency switching: */
+ struct clk *dram_core;
+ struct clk *dram_pll;
+ struct clk *dram_alt;
+ struct clk *dram_apb;
+
+ int freq_count;
+ struct imx8m_ddrc_freq freq_table[IMX8M_DDRC_MAX_FREQ_COUNT];
+};
+
+static struct imx8m_ddrc_freq *imx8m_ddrc_find_freq(struct imx8m_ddrc *priv,
+ unsigned long rate)
+{
+ struct imx8m_ddrc_freq *freq;
+ int i;
+
+ /*
+ * Firmware reports values in MT/s, so we round-down from Hz
+ * Rounding is extra generous to ensure a match.
+ */
+ rate = DIV_ROUND_CLOSEST(rate, 250000);
+ for (i = 0; i < priv->freq_count; ++i) {
+ freq = &priv->freq_table[i];
+ if (freq->rate == rate ||
+ freq->rate + 1 == rate ||
+ freq->rate - 1 == rate)
+ return freq;
+ }
+
+ return NULL;
+}
+
+static void imx8m_ddrc_smc_set_freq(int target_freq)
+{
+ struct arm_smccc_res res;
+ u32 online_cpus = 0;
+ int cpu;
+
+ local_irq_disable();
+
+ for_each_online_cpu(cpu)
+ online_cpus |= (1 << (cpu * 8));
+
+ /* change the ddr freqency */
+ arm_smccc_smc(IMX_SIP_DDR_DVFS, target_freq, online_cpus,
+ 0, 0, 0, 0, 0, &res);
+
+ local_irq_enable();
+}
+
+static struct clk *clk_get_parent_by_index(struct clk *clk, int index)
+{
+ struct clk_hw *hw;
+
+ hw = clk_hw_get_parent_by_index(__clk_get_hw(clk), index);
+
+ return hw ? hw->clk : NULL;
+}
+
+static int imx8m_ddrc_set_freq(struct device *dev, struct imx8m_ddrc_freq *freq)
+{
+ struct imx8m_ddrc *priv = dev_get_drvdata(dev);
+ struct clk *new_dram_core_parent;
+ struct clk *new_dram_alt_parent;
+ struct clk *new_dram_apb_parent;
+ int ret;
+
+ /*
+ * Fetch new parents
+ *
+ * new_dram_alt_parent and new_dram_apb_parent are optional but
+ * new_dram_core_parent is not.
+ */
+ new_dram_core_parent = clk_get_parent_by_index(
+ priv->dram_core, freq->dram_core_parent_index - 1);
+ if (!new_dram_core_parent) {
+ dev_err(dev, "failed to fetch new dram_core parent\n");
+ return -EINVAL;
+ }
+ if (freq->dram_alt_parent_index) {
+ new_dram_alt_parent = clk_get_parent_by_index(
+ priv->dram_alt,
+ freq->dram_alt_parent_index - 1);
+ if (!new_dram_alt_parent) {
+ dev_err(dev, "failed to fetch new dram_alt parent\n");
+ return -EINVAL;
+ }
+ } else
+ new_dram_alt_parent = NULL;
+
+ if (freq->dram_apb_parent_index) {
+ new_dram_apb_parent = clk_get_parent_by_index(
+ priv->dram_apb,
+ freq->dram_apb_parent_index - 1);
+ if (!new_dram_apb_parent) {
+ dev_err(dev, "failed to fetch new dram_apb parent\n");
+ return -EINVAL;
+ }
+ } else
+ new_dram_apb_parent = NULL;
+
+ /* increase reference counts and ensure clks are ON before switch */
+ ret = clk_prepare_enable(new_dram_core_parent);
+ if (ret) {
+ dev_err(dev, "failed to enable new dram_core parent: %d\n",
+ ret);
+ goto out;
+ }
+ ret = clk_prepare_enable(new_dram_alt_parent);
+ if (ret) {
+ dev_err(dev, "failed to enable new dram_alt parent: %d\n",
+ ret);
+ goto out_disable_core_parent;
+ }
+ ret = clk_prepare_enable(new_dram_apb_parent);
+ if (ret) {
+ dev_err(dev, "failed to enable new dram_apb parent: %d\n",
+ ret);
+ goto out_disable_alt_parent;
+ }
+
+ imx8m_ddrc_smc_set_freq(freq->smcarg);
+
+ /* update parents in clk tree after switch. */
+ ret = clk_set_parent(priv->dram_core, new_dram_core_parent);
+ if (ret)
+ dev_warn(dev, "failed to set dram_core parent: %d\n", ret);
+ if (new_dram_alt_parent) {
+ ret = clk_set_parent(priv->dram_alt, new_dram_alt_parent);
+ if (ret)
+ dev_warn(dev, "failed to set dram_alt parent: %d\n",
+ ret);
+ }
+ if (new_dram_apb_parent) {
+ ret = clk_set_parent(priv->dram_apb, new_dram_apb_parent);
+ if (ret)
+ dev_warn(dev, "failed to set dram_apb parent: %d\n",
+ ret);
+ }
+
+ /*
+ * Explicitly refresh dram PLL rate.
+ *
+ * Even if it's marked with CLK_GET_RATE_NOCACHE the rate will not be
+ * automatically refreshed when clk_get_rate is called on children.
+ */
+ clk_get_rate(priv->dram_pll);
+
+ /*
+ * clk_set_parent transfer the reference count from old parent.
+ * now we drop extra reference counts used during the switch
+ */
+ clk_disable_unprepare(new_dram_apb_parent);
+out_disable_alt_parent:
+ clk_disable_unprepare(new_dram_alt_parent);
+out_disable_core_parent:
+ clk_disable_unprepare(new_dram_core_parent);
+out:
+ return ret;
+}
+
+static int imx8m_ddrc_target(struct device *dev, unsigned long *freq, u32 flags)
+{
+ struct imx8m_ddrc *priv = dev_get_drvdata(dev);
+ struct imx8m_ddrc_freq *freq_info;
+ struct dev_pm_opp *new_opp;
+ unsigned long old_freq, new_freq;
+ int ret;
+
+ new_opp = devfreq_recommended_opp(dev, freq, flags);
+ if (IS_ERR(new_opp)) {
+ ret = PTR_ERR(new_opp);
+ dev_err(dev, "failed to get recommended opp: %d\n", ret);
+ return ret;
+ }
+ dev_pm_opp_put(new_opp);
+
+ old_freq = clk_get_rate(priv->dram_core);
+ if (*freq == old_freq)
+ return 0;
+
+ freq_info = imx8m_ddrc_find_freq(priv, *freq);
+ if (!freq_info)
+ return -EINVAL;
+
+ /*
+ * Read back the clk rate to verify switch was correct and so that
+ * we can report it on all error paths.
+ */
+ ret = imx8m_ddrc_set_freq(dev, freq_info);
+
+ new_freq = clk_get_rate(priv->dram_core);
+ if (ret)
+ dev_err(dev, "ddrc failed freq switch to %lu from %lu: error %d. now at %lu\n",
+ old_freq, *freq, ret, new_freq);
+ else if (*freq != new_freq)
+ dev_err(dev, "ddrc failed freq update to %lu from %lu, now at %lu\n",
+ old_freq, *freq, new_freq);
+ else
+ dev_dbg(dev, "ddrc freq set to %lu (was %lu)\n",
+ *freq, old_freq);
+
+ return ret;
+}
+
+static int imx8m_ddrc_get_cur_freq(struct device *dev, unsigned long *freq)
+{
+ struct imx8m_ddrc *priv = dev_get_drvdata(dev);
+
+ *freq = clk_get_rate(priv->dram_core);
+
+ return 0;
+}
+
+static int imx8m_ddrc_get_dev_status(struct device *dev,
+ struct devfreq_dev_status *stat)
+{
+ struct imx8m_ddrc *priv = dev_get_drvdata(dev);
+
+ stat->busy_time = 0;
+ stat->total_time = 0;
+ stat->current_frequency = clk_get_rate(priv->dram_core);
+
+ return 0;
+}
+
+static int imx8m_ddrc_init_freq_info(struct device *dev)
+{
+ struct imx8m_ddrc *priv = dev_get_drvdata(dev);
+ struct arm_smccc_res res;
+ int index;
+
+ /* An error here means DDR DVFS API not supported by firmware */
+ arm_smccc_smc(IMX_SIP_DDR_DVFS, IMX_SIP_DDR_DVFS_GET_FREQ_COUNT,
+ 0, 0, 0, 0, 0, 0, &res);
+ priv->freq_count = res.a0;
+ if (priv->freq_count <= 0 ||
+ priv->freq_count > IMX8M_DDRC_MAX_FREQ_COUNT)
+ return -ENODEV;
+
+ for (index = 0; index < priv->freq_count; ++index) {
+ struct imx8m_ddrc_freq *freq = &priv->freq_table[index];
+
+ arm_smccc_smc(IMX_SIP_DDR_DVFS, IMX_SIP_DDR_DVFS_GET_FREQ_INFO,
+ index, 0, 0, 0, 0, 0, &res);
+ /* Result should be strictly positive */
+ if ((long)res.a0 <= 0)
+ return -ENODEV;
+
+ freq->rate = res.a0;
+ freq->smcarg = index;
+ freq->dram_core_parent_index = res.a1;
+ freq->dram_alt_parent_index = res.a2;
+ freq->dram_apb_parent_index = res.a3;
+
+ /* dram_core has 2 options: dram_pll or dram_alt_root */
+ if (freq->dram_core_parent_index != 1 &&
+ freq->dram_core_parent_index != 2)
+ return -ENODEV;
+ /* dram_apb and dram_alt have exactly 8 possible parents */
+ if (freq->dram_alt_parent_index > 8 ||
+ freq->dram_apb_parent_index > 8)
+ return -ENODEV;
+ /* dram_core from alt requires explicit dram_alt parent */
+ if (freq->dram_core_parent_index == 2 &&
+ freq->dram_alt_parent_index == 0)
+ return -ENODEV;
+ }
+
+ return 0;
+}
+
+static int imx8m_ddrc_check_opps(struct device *dev)
+{
+ struct imx8m_ddrc *priv = dev_get_drvdata(dev);
+ struct imx8m_ddrc_freq *freq_info;
+ struct dev_pm_opp *opp;
+ unsigned long freq;
+ int i, opp_count;
+
+ /* Enumerate DT OPPs and disable those not supported by firmware */
+ opp_count = dev_pm_opp_get_opp_count(dev);
+ if (opp_count < 0)
+ return opp_count;
+ for (i = 0, freq = 0; i < opp_count; ++i, ++freq) {
+ opp = dev_pm_opp_find_freq_ceil(dev, &freq);
+ if (IS_ERR(opp)) {
+ dev_err(dev, "Failed enumerating OPPs: %ld\n",
+ PTR_ERR(opp));
+ return PTR_ERR(opp);
+ }
+ dev_pm_opp_put(opp);
+
+ freq_info = imx8m_ddrc_find_freq(priv, freq);
+ if (!freq_info) {
+ dev_info(dev, "Disable unsupported OPP %luHz %luMT/s\n",
+ freq, DIV_ROUND_CLOSEST(freq, 250000));
+ dev_pm_opp_disable(dev, freq);
+ }
+ }
+
+ return 0;
+}
+
+static void imx8m_ddrc_exit(struct device *dev)
+{
+ dev_pm_opp_of_remove_table(dev);
+}
+
+static int imx8m_ddrc_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct imx8m_ddrc *priv;
+ const char *gov = DEVFREQ_GOV_USERSPACE;
+ int ret;
+
+ priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+ if (!priv)
+ return -ENOMEM;
+
+ platform_set_drvdata(pdev, priv);
+
+ ret = imx8m_ddrc_init_freq_info(dev);
+ if (ret) {
+ dev_err(dev, "failed to init firmware freq info: %d\n", ret);
+ return ret;
+ }
+
+ priv->dram_core = devm_clk_get(dev, "core");
+ priv->dram_pll = devm_clk_get(dev, "pll");
+ priv->dram_alt = devm_clk_get(dev, "alt");
+ priv->dram_apb = devm_clk_get(dev, "apb");
+ if (IS_ERR(priv->dram_core) ||
+ IS_ERR(priv->dram_pll) ||
+ IS_ERR(priv->dram_alt) ||
+ IS_ERR(priv->dram_apb)) {
+ ret = PTR_ERR(priv->devfreq);
+ dev_err(dev, "failed to fetch clocks: %d\n", ret);
+ return ret;
+ }
+
+ ret = dev_pm_opp_of_add_table(dev);
+ if (ret < 0) {
+ dev_err(dev, "failed to get OPP table\n");
+ return ret;
+ }
+
+ ret = imx8m_ddrc_check_opps(dev);
+ if (ret < 0)
+ goto err;
+
+ priv->profile.polling_ms = 1000;
+ priv->profile.target = imx8m_ddrc_target;
+ priv->profile.get_dev_status = imx8m_ddrc_get_dev_status;
+ priv->profile.exit = imx8m_ddrc_exit;
+ priv->profile.get_cur_freq = imx8m_ddrc_get_cur_freq;
+ priv->profile.initial_freq = clk_get_rate(priv->dram_core);
+
+ priv->devfreq = devm_devfreq_add_device(dev, &priv->profile,
+ gov, NULL);
+ if (IS_ERR(priv->devfreq)) {
+ ret = PTR_ERR(priv->devfreq);
+ dev_err(dev, "failed to add devfreq device: %d\n", ret);
+ goto err;
+ }
+
+ return 0;
+
+err:
+ dev_pm_opp_of_remove_table(dev);
+ return ret;
+}
+
+static const struct of_device_id imx8m_ddrc_of_match[] = {
+ { .compatible = "fsl,imx8m-ddrc", },
+ { /* sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, imx8m_ddrc_of_match);
+
+static struct platform_driver imx8m_ddrc_platdrv = {
+ .probe = imx8m_ddrc_probe,
+ .driver = {
+ .name = "imx8m-ddrc-devfreq",
+ .of_match_table = of_match_ptr(imx8m_ddrc_of_match),
+ },
+};
+module_platform_driver(imx8m_ddrc_platdrv);
+
+MODULE_DESCRIPTION("i.MX8M DDR Controller frequency driver");
+MODULE_AUTHOR("Leonard Crestez <leonard.crestez@nxp.com>");
+MODULE_LICENSE("GPL v2");