Date:   Fri, 1 Feb 2019 10:43:07 +0700
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Andrew-sh Cheng <andrew-sh.cheng@...iatek.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        devicetree@...r.kernel.org, srv_heupstream@...iatek.com,
        linux-pm@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        Fan Chen <fan.chen@...iatek.com>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] devfreq: add mediatek cci devfreq

On Tue, Jan 29, 2019 at 1:36 PM Andrew-sh Cheng
<andrew-sh.cheng@...iatek.com> wrote:
>
> From: "Andrew-sh.Cheng" <andrew-sh.cheng@...iatek.com>
>
> For big/little cpu cluster architecture,
> not only CPU frequency, but CCI frequency will also affect performance.
>
> Little cores and cci share the same buck in Mediatek mt8183 IC,
> so we add a CCI devfreq which will get notification when buck voltage
> is changed, then CCI devfreq can set cci frequency as high as possible.
>
> Signed-off-by: Andrew-sh.Cheng <andrew-sh.cheng@...iatek.com>
> ---
>  drivers/devfreq/Kconfig              |   9 ++
>  drivers/devfreq/Makefile             |   1 +
>  drivers/devfreq/mt8183-cci-devfreq.c | 224 +++++++++++++++++++++++++++++++++++
>  3 files changed, 234 insertions(+)
>  create mode 100644 drivers/devfreq/mt8183-cci-devfreq.c
>
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index 6a172d3..0b14aab 100644
> --- a/drivers/devfreq/Kconfig
> +++ b/drivers/devfreq/Kconfig
> @@ -113,6 +113,15 @@ config ARM_RK3399_DMC_DEVFREQ
>            It sets the frequency for the memory controller and reads the usage counts
>            from hardware.
>
> +config ARM_MT8183_CCI_DEVFREQ
> +       tristate "MT8183 CCI DEVFREQ Driver"
> +       depends on ARM_MEDIATEK_CPUFREQ
> +       help
> +               This adds devfreq for cci clock

It might be nice to spell out that CCI stands for "Cache Coherent Interconnect".

> +               which is shared the same regulator with cpu cluster.
> +               It can track buck voltage and update a proper cci frequency.
> +               Use notification to get regulator status.
> +
>  source "drivers/devfreq/event/Kconfig"
>
>  endif # PM_DEVFREQ
> diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
> index 32b8d4d..25afe8c 100644
> --- a/drivers/devfreq/Makefile
> +++ b/drivers/devfreq/Makefile
> @@ -11,6 +11,7 @@ obj-$(CONFIG_DEVFREQ_GOV_PASSIVE)     += governor_passive.o
>  obj-$(CONFIG_ARM_EXYNOS_BUS_DEVFREQ)   += exynos-bus.o
>  obj-$(CONFIG_ARM_RK3399_DMC_DEVFREQ)   += rk3399_dmc.o
>  obj-$(CONFIG_ARM_TEGRA_DEVFREQ)                += tegra-devfreq.o
> +obj-$(CONFIG_ARM_MT8183_CCI_DEVFREQ)   += mt8183-cci-devfreq.o
>
>  # DEVFREQ Event Drivers
>  obj-$(CONFIG_PM_DEVFREQ_EVENT)         += event/
> diff --git a/drivers/devfreq/mt8183-cci-devfreq.c b/drivers/devfreq/mt8183-cci-devfreq.c
> new file mode 100644
> index 0000000..4837892
> --- /dev/null
> +++ b/drivers/devfreq/mt8183-cci-devfreq.c
> @@ -0,0 +1,224 @@
> +// SPDX-License-Identifier: GPL-2.0
> +//
> +// Copyright (c) 2018 MediaTek Inc.
> +#include <linux/cpu.h>
> +#include <linux/cpufreq.h>
> +#include <linux/devfreq.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/regulator/consumer.h>
> +
> +#include "governor.h"
> +
> +struct cci_devfreq_data {
> +       struct devfreq          *devfreq;
> +       struct regulator        *proc_reg;
> +       struct clk              *cci_clk;
> +       unsigned long           buck_volt;
> +       int                     volt_increasing;
> +       struct notifier_block   nb;
> +};
> +
> +static int mtk_cci_governor_get_target(struct devfreq *devfreq,
> +                                      unsigned long *freq)
> +{
> +       struct cci_devfreq_data *cci_devdata;
> +       int     i, opp_count;

No tab here: single space between int and i.

> +       struct dev_pm_opp       *opp;
> +       unsigned long   opp_rate, opp_voltage;
> +
> +       cci_devdata = dev_get_drvdata(devfreq->dev.parent);
> +
> +       /* find available frequency */
> +       opp_count = dev_pm_opp_get_opp_count(devfreq->dev.parent);
> +       for (i = 0, opp_rate = ULONG_MAX; i < opp_count; i++, opp_rate--) {
> +               opp = dev_pm_opp_find_freq_floor(devfreq->dev.parent,
> +                                                &opp_rate);

This is quite inefficient as each call to dev_pm_opp_find_freq_floor
may go through the whole OPP table (so your loop is O(n**2), but this
can be done in O(n) by simply walking through the list).

I'd just copy what dev_pm_opp_find_freq_ceil does
(https://elixir.bootlin.com/linux/v4.19/source/drivers/opp/core.c#L425).
Or maybe we need a new function in the opp core.

> +               opp_voltage = dev_pm_opp_get_voltage(opp);
> +               dev_pm_opp_put(opp);
> +
> +               if (opp_voltage <= cci_devdata->buck_volt)
> +                       break;
> +       }
> +       *freq = opp_rate;
> +
> +       return 0;
> +}
> +
> +static int mtk_cci_governor_event_handler(struct devfreq *devfreq,
> +                                         unsigned int event, void *data)
> +{
> +       return 0;
> +}
> +
> +static struct devfreq_governor mtk_cci_devfreq_governor = {
> +       .name = "voltage_monitor",
> +       .get_target_freq = mtk_cci_governor_get_target,
> +       .event_handler = mtk_cci_governor_event_handler,
> +};
> +
> +static int mtk_cci_devfreq_target(struct device *dev, unsigned long *freq,
> +                                 u32 flags)
> +{
> +       struct cci_devfreq_data *cci_devdata;
> +
> +       cci_devdata = dev_get_drvdata(dev);
> +
> +       clk_set_rate(cci_devdata->cci_clk, *freq);
> +
> +       return 0;
> +}
> +
> +static struct devfreq_dev_profile cci_devfreq_profile = {
> +       .polling_ms     = 0,
> +       .target         = mtk_cci_devfreq_target,
> +};
> +
> +static int cci_devfreq_regulator_notifier(struct notifier_block *nb,
> +                                         unsigned long val, void *data)
> +{
> +       struct cci_devfreq_data *cci_devdata =
> +               container_of(nb, struct cci_devfreq_data, nb);
> +
> +       /* deal with reduce frequency */
> +       if (val & REGULATOR_EVENT_PRE_VOLTAGE_CHANGE) {
> +               struct pre_voltage_change_data *pvc_data = data;
> +
> +               if (pvc_data->old_uV > pvc_data->min_uV) {
> +                       cci_devdata->volt_increasing = 0;
> +                       cci_devdata->buck_volt =
> +                               (unsigned long)(pvc_data->min_uV);
> +                       mutex_lock(&cci_devdata->devfreq->lock);
> +                       update_devfreq(cci_devdata->devfreq);
> +                       mutex_unlock(&cci_devdata->devfreq->lock);
> +               } else {
> +                       cci_devdata->volt_increasing = 1;
> +               }
> +       }
> +       /* deal with abort reduce frequency */
> +       if ((val & REGULATOR_EVENT_ABORT_VOLTAGE_CHANGE) ||
> +           /* deal with increase frequency */
> +           ((val & REGULATOR_EVENT_VOLTAGE_CHANGE) &&
> +            cci_devdata->volt_increasing == 1)) {
> +               cci_devdata->buck_volt = (unsigned long)data;
> +               mutex_lock(&cci_devdata->devfreq->lock);
> +               update_devfreq(cci_devdata->devfreq);
> +               mutex_unlock(&cci_devdata->devfreq->lock);
> +       }
> +
> +       return 0;
> +}
> +
> +static int mtk_cci_devfreq_probe(struct platform_device *pdev)
> +{
> +       struct device *cci_dev = &pdev->dev;
> +       struct cci_devfreq_data *cci_devdata;
> +       struct notifier_block *nb;
> +       int ret;
> +
> +       dev_pm_opp_of_add_table(&pdev->dev);
> +
> +       cci_devdata = devm_kzalloc(cci_dev, sizeof(*cci_devdata), GFP_KERNEL);
> +       if (!cci_devdata)
> +               return -ENOMEM;
> +       nb = &cci_devdata->nb;
> +       cci_devdata->cci_clk = ERR_PTR(-ENODEV);

This one is useless as you set cci_clk again just below.

> +       cci_devdata->proc_reg = ERR_PTR(-ENODEV);

For this one, I'd just create 2 goto targets below, instead of those
ifs in the error path.

> +
> +       cci_devdata->cci_clk = clk_get(cci_dev, "cci_clock");
> +       ret = PTR_ERR_OR_ZERO(cci_devdata->cci_clk);
> +       if (ret) {
> +               if (ret == -EPROBE_DEFER)
> +                       pr_err("cci clock not ready, retry\n");
> +               else
> +                       pr_err("no clock for cci: %d\n", ret);
> +
> +               goto out_free_resources;
> +       }
> +
> +       cci_devdata->proc_reg = regulator_get_optional(cci_dev, "proc");
> +       ret = PTR_ERR_OR_ZERO(cci_devdata->proc_reg);
> +       if (ret) {
> +               if (ret == -EPROBE_DEFER)
> +                       pr_err("cci regulator not ready, retry\n");
> +               else
> +                       pr_err("no regulator for cci: %d\n", ret);
> +
> +               goto out_free_resources;
> +       }
> +
> +       platform_set_drvdata(pdev, cci_devdata);
> +
> +       /* create cci_devfreq and add to cci device.
> +        * governor is voltage_monitor.
> +        * governor will get platform_device data to make decision.
> +        */
> +       cci_devdata->devfreq = devm_devfreq_add_device(cci_dev,
> +                                                      &cci_devfreq_profile,
> +                                                      "voltage_monitor",
> +                                                      NULL);
> +
> +       nb->notifier_call = cci_devfreq_regulator_notifier;
> +       regulator_register_notifier(cci_devdata->proc_reg,
> +                                   nb);
> +
> +       return 0;
> +
> +out_free_resources:
> +       if (!IS_ERR(cci_devdata->cci_clk))
> +               clk_put(cci_devdata->cci_clk);
> +       if (!IS_ERR(cci_devdata->proc_reg))
> +               regulator_put(cci_devdata->proc_reg);
> +
> +       return ret;
> +}
> +
> +static const struct of_device_id mediatek_cci_devfreq_of_match[] = {
> +       { .compatible = "mediatek,mt8183-cci" },
> +       { },
> +};
> +MODULE_DEVICE_TABLE(of, mediatek_cci_devfreq_of_match);
> +
> +static struct platform_driver cci_devfreq_driver = {
> +       .probe  = mtk_cci_devfreq_probe,
> +       .driver = {
> +               .name = "mediatek-cci-devfreq",
> +               .of_match_table = mediatek_cci_devfreq_of_match,
> +       },
> +};
> +
> +static int __init mtk_cci_devfreq_init(void)
> +{
> +       int ret = 0;
> +
> +       ret = devfreq_add_governor(&mtk_cci_devfreq_governor);
> +       if (ret) {
> +               pr_err("%s: failed to add governor: %d\n", __func__, ret);
> +               return ret;
> +       }
> +
> +       ret = platform_driver_register(&cci_devfreq_driver);
> +       if (ret)
> +               devfreq_remove_governor(&mtk_cci_devfreq_governor);
> +
> +       return ret;
> +}
> +module_init(mtk_cci_devfreq_init)
> +
> +static void __exit mtk_cci_devfreq_exit(void)
> +{
> +       int ret = 0;
> +
> +       platform_driver_unregister(&cci_devfreq_driver);
> +
> +       ret = devfreq_remove_governor(&mtk_cci_devfreq_governor);
> +       if (ret)
> +               pr_err("%s: failed to remove governor: %d\n", __func__, ret);
> +}
> +module_exit(mtk_cci_devfreq_exit)
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_DESCRIPTION("Mediatek CCI devfreq driver");
> +MODULE_AUTHOR("andrew-sh.cheng");
> +
> --
> 1.8.1.1.dirty
>
>
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