Date:   Mon, 21 Nov 2016 17:08:41 -0800
From:   Markus Mayer <mmayer@...adcom.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>
Cc:     Power Management List <linux-pm@...r.kernel.org>,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] cpufreq: brcmstb-cpufreq: CPUfreq driver for older
 Broadcom STB SoCs

On 21 November 2016 at 17:06, Markus Mayer <code@...yer.net> wrote:
> From: Markus Mayer <mmayer@...adcom.com>
>
> This CPUfreq driver provides basic frequency scaling for older Broadcom
> STB SoCs that do not use AVS firmware with DVFS support. There is no
> support for voltage scaling.
>
> Signed-off-by: Markus Mayer <mmayer@...adcom.com>
> ---

I meant to add this to the patch:

Changes since v2:
    - removed brcmstb_cpufreq_get(), using cpufreq_generic_get() instead
    - replaced calls to cpufreq_table_validate_and_show() and
      cpumask_setall() with a call to cpufreq_generic_init()
    - removed code that would set policy->cur, leaving it up to the
      framework to do so
    - simplified show_brcmstb_safe_freq(), re-using already existing data

>  drivers/cpufreq/Kconfig.arm       |  12 ++
>  drivers/cpufreq/Makefile          |   1 +
>  drivers/cpufreq/brcmstb-cpufreq.c | 381 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 394 insertions(+)
>  create mode 100644 drivers/cpufreq/brcmstb-cpufreq.c
>
> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> index 920c469..36422af 100644
> --- a/drivers/cpufreq/Kconfig.arm
> +++ b/drivers/cpufreq/Kconfig.arm
> @@ -33,6 +33,18 @@ config ARM_BRCMSTB_AVS_CPUFREQ_DEBUG
>
>           If in doubt, say N.
>
> +config ARM_BRCMSTB_CPUFREQ
> +       tristate "Broadcom STB CPUfreq driver"
> +       depends on ARCH_BRCMSTB || COMPILE_TEST
> +       default y
> +       help
> +         Some Broadcom SoCs offer multiple operating frequencies that CPUfreq
> +         can take advantage of to improve energy efficiency.
> +
> +         Say Y, if you have a supported Broadcom SoC. If your Broadcom SoC
> +         has AVS firmware with support for frequency and voltage scaling,
> +         say N here and enable ARM_BRCMSTB_AVS_CPUFREQ instead.
> +
>  config ARM_DT_BL_CPUFREQ
>         tristate "Generic probing via DT for ARM big LITTLE CPUfreq driver"
>         depends on ARM_BIG_LITTLE_CPUFREQ && OF
> diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> index 1e46c39..23700aa 100644
> --- a/drivers/cpufreq/Makefile
> +++ b/drivers/cpufreq/Makefile
> @@ -52,6 +52,7 @@ obj-$(CONFIG_ARM_BIG_LITTLE_CPUFREQ)  += arm_big_little.o
>  obj-$(CONFIG_ARM_DT_BL_CPUFREQ)                += arm_big_little_dt.o
>
>  obj-$(CONFIG_ARM_BRCMSTB_AVS_CPUFREQ)  += brcmstb-avs-cpufreq.o
> +obj-$(CONFIG_ARM_BRCMSTB_CPUFREQ)      += brcmstb-cpufreq.o
>  obj-$(CONFIG_ARCH_DAVINCI)             += davinci-cpufreq.o
>  obj-$(CONFIG_UX500_SOC_DB8500)         += dbx500-cpufreq.o
>  obj-$(CONFIG_ARM_EXYNOS5440_CPUFREQ)   += exynos5440-cpufreq.o
> diff --git a/drivers/cpufreq/brcmstb-cpufreq.c b/drivers/cpufreq/brcmstb-cpufreq.c
> new file mode 100644
> index 0000000..0270789
> --- /dev/null
> +++ b/drivers/cpufreq/brcmstb-cpufreq.c
> @@ -0,0 +1,381 @@
> +/*
> + * CPU frequency scaling for Broadcom set top box SoCs
> + *
> + * Copyright (c) 2016 Broadcom
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation version 2.
> + *
> + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
> + * kind, whether express or implied; without even the implied warranty
> + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/clk-provider.h>
> +#include <linux/cpufreq.h>
> +#include <linux/module.h>
> +#include <linux/of_address.h>
> +#include <linux/platform_device.h>
> +
> +#define BRCMSTB_CPUFREQ_PREFIX "brcmstb"
> +#define BRCMSTB_CPUFREQ_NAME   BRCMSTB_CPUFREQ_PREFIX "-cpufreq"
> +
> +/* We search for these compatible strings. */
> +#define BRCMSTB_DT_CPU_CLK_CTRL        "brcm,brcmstb-cpu-clk-div"
> +#define BRCMSTB_DT_MEMC_DDR    "brcm,brcmstb-memc-ddr"
> +#define BRCM_AVS_CPU_DATA      "brcm,avs-cpu-data-mem"
> +
> +/* We also need a few clocks in device tree. These are node names. */
> +#define BRCMSTB_CLK_MDIV_CH0   "cpu_mdiv_ch0"
> +#define BRCMSTB_CLK_NDIV_INT   "cpu_ndiv_int"
> +#define BRCMSTB_CLK_SW_SCB     "sw_scb"
> +
> +#define BRCMSTB_TBL_SAFE_MODE  BIT(0)
> +#define BRCMSTB_REG_SAFE_MODE  BIT(4)
> +
> +#define TRANSITION_LATENCY     (25 * 1000)     /* 25 us */
> +
> +/* This is as low as we'll go in the frequency table. */
> +#define MIN_CPU_FREQ           (100 * 1000)    /* in kHz */
> +
> +struct private_data {
> +       void __iomem *cpu_clk_ctrl_reg;
> +       struct device *dev;
> +};
> +
> +/* Count the active memory controllers in the system. */
> +static int count_memory_controllers(void)
> +{
> +       struct device_node *np = NULL;
> +       int i = 0;
> +
> +       do {
> +               np = of_find_compatible_node(np, NULL, BRCMSTB_DT_MEMC_DDR);
> +               if (of_device_is_available(np))
> +                       i++;
> +               of_node_put(np);
> +       } while (np);
> +
> +       return i;
> +}
> +
> +static int get_frequencies(const struct cpufreq_policy *policy,
> +                          unsigned int *vco_freq, unsigned int *cpu_freq,
> +                          unsigned int *scb_freq)
> +{
> +       struct clk *cpu_ndiv_int, *sw_scb;
> +
> +       cpu_ndiv_int = __clk_lookup(BRCMSTB_CLK_NDIV_INT);
> +       if (!cpu_ndiv_int)
> +               return -ENODEV;
> +
> +       sw_scb = __clk_lookup(BRCMSTB_CLK_SW_SCB);
> +       if (!sw_scb)
> +               return -ENODEV;
> +
> +       /* return frequencies in kHz */
> +       *vco_freq = clk_get_rate(cpu_ndiv_int) / 1000;
> +       *cpu_freq = clk_get_rate(policy->clk) / 1000;
> +       *scb_freq = clk_get_rate(sw_scb) / 1000;
> +
> +       return 0;
> +}
> +
> +/*
> + * Safe mode: When set, the CPU's bus unit is being throttled. This is done to
> + * avoid buffer overflows when the CPU-to-bus-clock ratio is low.
> + *
> + * The formula as to what constitutes a low CPU-to-bus-clock ratio takes into
> + * account the number of memory controllers active in the system and the SCB
> + * frequency. More memory controllers means safe mode is required starting at
> + * higher frequencies.
> + *
> + * For 1 memory controller, cpu_freq/scb_freq must be greater than or equal to
> + * 2 to not require safe mode.
> + *
> + * For 2 or 3 memory controllers, cpu_freq/scb_freq must be greater than or
> + * equal 3 to not require safe mode.
> + */
> +
> +static int freq_requires_safe_mode(unsigned int cpu_freq, unsigned int scb_freq,
> +                                  int num_memc)
> +{
> +       unsigned int safe_ratio;
> +
> +       switch (num_memc) {
> +       case 1:
> +               safe_ratio = 2;
> +               break;
> +       case 2:
> +       case 3:
> +               safe_ratio = 3;
> +               break;
> +       default:
> +               return -EINVAL;
> +       }
> +
> +       return ((cpu_freq / scb_freq) < safe_ratio);
> +}
> +
> +static struct cpufreq_frequency_table *
> +brcmstb_get_freq_table(const struct cpufreq_policy *policy)
> +{
> +       unsigned int cpu_freq, vco_freq, scb_freq, mdiv, init_mdiv, f;
> +       struct cpufreq_frequency_table *table;
> +       struct private_data *priv;
> +       int num_memc, ret;
> +       unsigned int i = 0;
> +
> +       ret = get_frequencies(policy, &vco_freq, &cpu_freq, &scb_freq);
> +       if (ret)
> +               return ERR_PTR(ret);
> +
> +       priv = policy->driver_data;
> +       num_memc = count_memory_controllers();
> +
> +       /* Calculate the initial mdiv value. We'll increment mdiv from here. */
> +       init_mdiv = vco_freq / cpu_freq;
> +
> +       /* Count how many frequencies we'll offer. */
> +       f = cpu_freq;
> +       for (mdiv = init_mdiv; f >= MIN_CPU_FREQ; mdiv++, f = vco_freq / mdiv) {
> +               /* We only want to use "whole" MHz. */
> +               if ((f % 1000) == 0)
> +                       i++;
> +       }
> +
> +       table = devm_kzalloc(priv->dev, (i + 1) * sizeof(*table), GFP_KERNEL);
> +       if (!table)
> +               return ERR_PTR(-ENOMEM);
> +
> +       /* Now, fill the table. */
> +       f = cpu_freq;
> +       i = 0;
> +       for (mdiv = init_mdiv; f >= MIN_CPU_FREQ; mdiv++, f = vco_freq / mdiv) {
> +               if ((f % 1000) == 0) {
> +                       table[i].frequency = f;
> +                       ret = freq_requires_safe_mode(f, scb_freq, num_memc);
> +                       if (ret < 0)
> +                               return ERR_PTR(ret);
> +                       if (ret > 0)
> +                               table[i].driver_data |= BRCMSTB_TBL_SAFE_MODE;
> +                       i++;
> +               }
> +       }
> +       table[i].frequency = CPUFREQ_TABLE_END;
> +
> +       return table;
> +}
> +
> +static int brcmstb_target_index(struct cpufreq_policy *policy,
> +                               unsigned int index)
> +{
> +       struct cpufreq_frequency_table *entry;
> +       struct private_data *priv;
> +       int ret, safe_mode_needed;
> +       u32 reg;
> +
> +       priv = policy->driver_data;
> +       entry = &policy->freq_table[index];
> +       safe_mode_needed = entry->driver_data & BRCMSTB_TBL_SAFE_MODE;
> +
> +       reg = readl(priv->cpu_clk_ctrl_reg);
> +       if (safe_mode_needed && !(reg & BRCMSTB_REG_SAFE_MODE)) {
> +               reg |= BRCMSTB_REG_SAFE_MODE;
> +               writel(reg, priv->cpu_clk_ctrl_reg);
> +       }
> +       ret = clk_set_rate(policy->clk, entry->frequency * 1000);
> +       if (!ret && !safe_mode_needed && (reg & BRCMSTB_REG_SAFE_MODE)) {
> +               reg &= ~BRCMSTB_REG_SAFE_MODE;
> +               writel(reg, priv->cpu_clk_ctrl_reg);
> +       }
> +
> +       return ret;
> +}
> +
> +/*
> + * All initialization code that we only want to execute once goes here. Setup
> + * code that can be re-tried on every core (if it failed before) can go into
> + * brcm_avs_cpufreq_init().
> + */
> +static int brcmstb_prepare_init(struct platform_device *pdev)
> +{
> +       struct private_data *priv;
> +       struct resource *res;
> +       struct device *dev;
> +
> +       /*
> +        * If the BRCM STB AVS CPUfreq driver is supported, we bail, so that
> +        * the more modern approach implementing DVFS in firmware can be used.
> +        */
> +       if (IS_ENABLED(CONFIG_ARM_BRCM_AVS_CPUFREQ)) {
> +               struct device_node *np;
> +
> +               np = of_find_compatible_node(NULL, NULL, BRCM_AVS_CPU_DATA);
> +               if (np) {
> +                       of_node_put(np);
> +                       return -ENXIO;
> +               }
> +       }
> +
> +       dev = &pdev->dev;
> +
> +       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +       if (!priv)
> +               return -ENOMEM;
> +
> +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +       priv->cpu_clk_ctrl_reg = devm_ioremap_resource(dev, res);
> +       if (IS_ERR(priv->cpu_clk_ctrl_reg)) {
> +               dev_err(dev, "couldn't map DT entry %s\n",
> +                       BRCMSTB_DT_CPU_CLK_CTRL);
> +               return -ENODEV;
> +       }
> +
> +       priv->dev = dev;
> +       platform_set_drvdata(pdev, priv);
> +
> +       return 0;
> +}
> +
> +static int brcmstb_cpu_init(struct cpufreq_policy *policy)
> +{
> +       struct cpufreq_frequency_table *freq_table;
> +       struct platform_device *pdev;
> +       struct private_data *priv;
> +       struct clk *cpu_mdiv_ch0;
> +       struct device *dev;
> +       int ret;
> +
> +       cpu_mdiv_ch0 = __clk_lookup(BRCMSTB_CLK_MDIV_CH0);
> +       if (!cpu_mdiv_ch0)
> +               return -ENODEV;
> +
> +       pdev = cpufreq_get_driver_data();
> +       priv = platform_get_drvdata(pdev);
> +       dev = &pdev->dev;
> +
> +       policy->clk = cpu_mdiv_ch0;
> +       policy->driver_data = priv;
> +
> +       freq_table = brcmstb_get_freq_table(policy);
> +       if (IS_ERR(freq_table)) {
> +               ret = PTR_ERR(freq_table);
> +               dev_err(dev, "Couldn't determine frequency table (%d).\n", ret);
> +               if (ret == -EINVAL)
> +                       dev_emerg(dev,
> +                               "Invalid number of memory controllers -- %d!\n",
> +                               count_memory_controllers());
> +               return ret;
> +       }
> +
> +       ret = cpufreq_generic_init(policy, freq_table, TRANSITION_LATENCY);
> +       if (!ret)
> +               dev_info(dev, "registered\n");
> +
> +       return ret;
> +}
> +
> +/* Shows the number of memory controllers. */
> +static ssize_t show_brcmstb_num_memc(struct cpufreq_policy *policy, char *buf)
> +{
> +       return sprintf(buf, "%u\n", count_memory_controllers());
> +}
> +
> +/* Shows vco_freq, cpu_freq, and scb_freq in kHz. */
> +static ssize_t show_brcmstb_freqs(struct cpufreq_policy *policy, char *buf)
> +{
> +       unsigned int vco_freq, cpu_freq, scb_freq;
> +       int ret;
> +
> +       ret = get_frequencies(policy, &vco_freq, &cpu_freq, &scb_freq);
> +       if (ret)
> +               return sprintf(buf, "<unknown>\n");
> +
> +       return sprintf(buf, "%u %u %u\n", vco_freq, cpu_freq, scb_freq);
> +}
> +
> +/* Shows the lowest frequency (in kHz) that can be used without "safe mode". */
> +static ssize_t show_brcmstb_safe_freq(struct cpufreq_policy *policy, char *buf)
> +{
> +       struct cpufreq_frequency_table *entry;
> +       unsigned int safe_freq = 0;
> +
> +       cpufreq_for_each_valid_entry(entry, policy->freq_table) {
> +               if (!(entry->driver_data & BRCMSTB_TBL_SAFE_MODE))
> +                       safe_freq = entry->frequency;
> +       }
> +
> +       return sprintf(buf, "%u\n", safe_freq);
> +}
> +
> +cpufreq_freq_attr_ro(brcmstb_num_memc);
> +cpufreq_freq_attr_ro(brcmstb_freqs);
> +cpufreq_freq_attr_ro(brcmstb_safe_freq);
> +
> +static struct freq_attr *brcmstb_cpufreq_attr[] = {
> +       &cpufreq_freq_attr_scaling_available_freqs,
> +       &brcmstb_num_memc,
> +       &brcmstb_freqs,
> +       &brcmstb_safe_freq,
> +       NULL
> +};
> +
> +static struct cpufreq_driver brcmstb_driver = {
> +       .flags          = CPUFREQ_NEED_INITIAL_FREQ_CHECK,
> +       .verify         = cpufreq_generic_frequency_table_verify,
> +       .target_index   = brcmstb_target_index,
> +       .get            = cpufreq_generic_get,
> +       .init           = brcmstb_cpu_init,
> +       .attr           = brcmstb_cpufreq_attr,
> +       .name           = BRCMSTB_CPUFREQ_PREFIX,
> +};
> +
> +static int brcmstb_cpufreq_probe(struct platform_device *pdev)
> +{
> +       int ret;
> +
> +       ret = brcmstb_prepare_init(pdev);
> +       if (ret)
> +               return ret;
> +
> +       brcmstb_driver.driver_data = pdev;
> +
> +       return cpufreq_register_driver(&brcmstb_driver);
> +}
> +
> +static int brcmstb_cpufreq_remove(struct platform_device *pdev)
> +{
> +       int ret;
> +
> +       ret = cpufreq_unregister_driver(&brcmstb_driver);
> +       if (ret)
> +               return ret;
> +
> +       platform_set_drvdata(pdev, NULL);
> +
> +       return 0;
> +}
> +
> +static const struct of_device_id brcmstb_cpufreq_match[] = {
> +       { .compatible = BRCMSTB_DT_CPU_CLK_CTRL },
> +       { }
> +};
> +MODULE_DEVICE_TABLE(platform, brcmstb_cpufreq_match);
> +
> +static struct platform_driver brcmstb_cpufreq_platdrv = {
> +       .driver = {
> +               .name   = BRCMSTB_CPUFREQ_NAME,
> +               .of_match_table = brcmstb_cpufreq_match,
> +       },
> +       .probe          = brcmstb_cpufreq_probe,
> +       .remove         = brcmstb_cpufreq_remove,
> +};
> +module_platform_driver(brcmstb_cpufreq_platdrv);
> +
> +MODULE_AUTHOR("Markus Mayer <mmayer@...adcom.com>");
> +MODULE_DESCRIPTION("CPUfreq driver for Broadcom STB SoCs");
> +MODULE_LICENSE("GPL");
> --
> 2.7.4
>

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