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Subject: Re: [TEGRA194_CPUFREQ PATCH v6 3/3] cpufreq: Add Tegra194 cpufreq
 driver
To:     Jon Hunter <jonathanh@nvidia.com>, <rjw@rjwysocki.net>,
        <viresh.kumar@linaro.org>, <catalin.marinas@arm.com>,
        <will@kernel.org>, <thierry.reding@gmail.com>,
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        <devicetree@vger.kernel.org>, <talho@nvidia.com>,
        <linux-pm@vger.kernel.org>, <linux-tegra@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
CC:     <bbasu@nvidia.com>, <mperttunen@nvidia.com>,
        Sumit Gupta <sumitg@nvidia.com>
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From:   Sumit Gupta <sumitg@nvidia.com>
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>> Add support for CPU frequency scaling on Tegra194. The frequency
>> of each core can be adjusted by writing a clock divisor value to
>> a MSR on the core. The range of valid divisors is queried from
>> the BPMP.
>>
>> Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>> ---
>>   drivers/cpufreq/Kconfig.arm        |   7 +
>>   drivers/cpufreq/Makefile           |   1 +
>>   drivers/cpufreq/tegra194-cpufreq.c | 397 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 405 insertions(+)
>>   create mode 100644 drivers/cpufreq/tegra194-cpufreq.c
>>
>> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
>> index 15c1a12..7e99a46 100644
>> --- a/drivers/cpufreq/Kconfig.arm
>> +++ b/drivers/cpufreq/Kconfig.arm
>> @@ -314,6 +314,13 @@ config ARM_TEGRA186_CPUFREQ
>>   	help
>>   	  This adds the CPUFreq driver support for Tegra186 SOCs.
>>   
>> +config ARM_TEGRA194_CPUFREQ
>> +	tristate "Tegra194 CPUFreq support"
>> +	depends on ARCH_TEGRA_194_SOC && TEGRA_BPMP
>> +	default y
>> +	help
>> +	  This adds CPU frequency driver support for Tegra194 SOCs.
>> +
>>   config ARM_TI_CPUFREQ
>>   	bool "Texas Instruments CPUFreq support"
>>   	depends on ARCH_OMAP2PLUS
>> diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
>> index f6670c4..66b5563 100644
>> --- a/drivers/cpufreq/Makefile
>> +++ b/drivers/cpufreq/Makefile
>> @@ -83,6 +83,7 @@ obj-$(CONFIG_ARM_TANGO_CPUFREQ)		+= tango-cpufreq.o
>>   obj-$(CONFIG_ARM_TEGRA20_CPUFREQ)	+= tegra20-cpufreq.o
>>   obj-$(CONFIG_ARM_TEGRA124_CPUFREQ)	+= tegra124-cpufreq.o
>>   obj-$(CONFIG_ARM_TEGRA186_CPUFREQ)	+= tegra186-cpufreq.o
>> +obj-$(CONFIG_ARM_TEGRA194_CPUFREQ)	+= tegra194-cpufreq.o
>>   obj-$(CONFIG_ARM_TI_CPUFREQ)		+= ti-cpufreq.o
>>   obj-$(CONFIG_ARM_VEXPRESS_SPC_CPUFREQ)	+= vexpress-spc-cpufreq.o
>>   
>> diff --git a/drivers/cpufreq/tegra194-cpufreq.c b/drivers/cpufreq/tegra194-cpufreq.c
>> new file mode 100644
>> index 0000000..b52a5e2
>> --- /dev/null
>> +++ b/drivers/cpufreq/tegra194-cpufreq.c
>> @@ -0,0 +1,397 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (c) 2020, NVIDIA CORPORATION. All rights reserved
>> + */
>> +
>> +#include <linux/cpu.h>
>> +#include <linux/cpufreq.h>
>> +#include <linux/delay.h>
>> +#include <linux/dma-mapping.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/slab.h>
>> +
>> +#include <asm/smp_plat.h>
>> +
>> +#include <soc/tegra/bpmp.h>
>> +#include <soc/tegra/bpmp-abi.h>
>> +
>> +#define KHZ                     1000
>> +#define REF_CLK_MHZ             408 /* 408 MHz */
>> +#define US_DELAY                500
>> +#define US_DELAY_MIN            2
>> +#define CPUFREQ_TBL_STEP_HZ     (50 * KHZ * KHZ)
>> +#define MAX_CNT                 ~0U
>> +
>> +/* cpufreq transisition latency */
>> +#define TEGRA_CPUFREQ_TRANSITION_LATENCY (300 * 1000) /* unit in nanoseconds */
>> +
>> +enum cluster {
>> +	CLUSTER0,
>> +	CLUSTER1,
>> +	CLUSTER2,
>> +	CLUSTER3,
>> +	MAX_CLUSTERS,
>> +};
>> +
>> +struct tegra194_cpufreq_data {
>> +	void __iomem *regs;
>> +	size_t num_clusters;
>> +	struct cpufreq_frequency_table **tables;
>> +};
>> +
>> +struct tegra_cpu_ctr {
>> +	u32 cpu;
>> +	u32 delay;
>> +	u32 coreclk_cnt, last_coreclk_cnt;
>> +	u32 refclk_cnt, last_refclk_cnt;
>> +};
>> +
>> +struct read_counters_work {
>> +	struct work_struct work;
>> +	struct tegra_cpu_ctr c;
>> +};
>> +
>> +static struct workqueue_struct *read_counters_wq;
>> +
>> +static enum cluster get_cpu_cluster(u8 cpu)
>> +{
>> +	return MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
>> +}
>> +
>> +/*
>> + * Read per-core Read-only system register NVFREQ_FEEDBACK_EL1.
>> + * The register provides frequency feedback information to
>> + * determine the average actual frequency a core has run at over
>> + * a period of time.
>> + *	[31:0] PLLP counter: Counts at fixed frequency (408 MHz)
>> + *	[63:32] Core clock counter: counts on every core clock cycle
>> + *			where the core is architecturally clocking
>> + */
>> +static u64 read_freq_feedback(void)
>> +{
>> +	u64 val = 0;
>> +
>> +	asm volatile("mrs %0, s3_0_c15_c0_5" : "=r" (val) : );
>> +
>> +	return val;
>> +}
>> +
>> +static inline u32 map_ndiv_to_freq(struct mrq_cpu_ndiv_limits_response
>> +				   *nltbl, u16 ndiv)
>> +{
>> +	return nltbl->ref_clk_hz / KHZ * ndiv / (nltbl->pdiv * nltbl->mdiv);
>> +}
>> +
>> +static void tegra_read_counters(struct work_struct *work)
>> +{
>> +	struct read_counters_work *read_counters_work;
>> +	struct tegra_cpu_ctr *c;
>> +	u64 val;
>> +
>> +	/*
>> +	 * ref_clk_counter(32 bit counter) runs on constant clk,
>> +	 * pll_p(408MHz).
>> +	 * It will take = 2 ^ 32 / 408 MHz to overflow ref clk counter
>> +	 *              = 10526880 usec = 10.527 sec to overflow
>> +	 *
>> +	 * Like wise core_clk_counter(32 bit counter) runs on core clock.
>> +	 * It's synchronized to crab_clk (cpu_crab_clk) which runs at
>> +	 * freq of cluster. Assuming max cluster clock ~2000MHz,
>> +	 * It will take = 2 ^ 32 / 2000 MHz to overflow core clk counter
>> +	 *              = ~2.147 sec to overflow
>> +	 */
>> +	read_counters_work = container_of(work, struct read_counters_work,
>> +					  work);
>> +	c = &read_counters_work->c;
>> +
>> +	val = read_freq_feedback();
>> +	c->last_refclk_cnt = lower_32_bits(val);
>> +	c->last_coreclk_cnt = upper_32_bits(val);
>> +	udelay(c->delay);
>> +	val = read_freq_feedback();
>> +	c->refclk_cnt = lower_32_bits(val);
>> +	c->coreclk_cnt = upper_32_bits(val);
>> +}
>> +
>> +/*
>> + * Return instantaneous cpu speed
>> + * Instantaneous freq is calculated as -
>> + * -Takes sample on every query of getting the freq.
>> + *	- Read core and ref clock counters;
>> + *	- Delay for X us
>> + *	- Read above cycle counters again
>> + *	- Calculates freq by subtracting current and previous counters
>> + *	  divided by the delay time or eqv. of ref_clk_counter in delta time
>> + *	- Return Kcycles/second, freq in KHz
>> + *
>> + *	delta time period = x sec
>> + *			  = delta ref_clk_counter / (408 * 10^6) sec
>> + *	freq in Hz = cycles/sec
>> + *		   = (delta cycles / x sec
>> + *		   = (delta cycles * 408 * 10^6) / delta ref_clk_counter
>> + *	in KHz	   = (delta cycles * 408 * 10^3) / delta ref_clk_counter
>> + *
>> + * @cpu - logical cpu whose freq to be updated
>> + * Returns freq in KHz on success, 0 if cpu is offline
>> + */
>> +static unsigned int tegra194_get_speed_common(u32 cpu, u32 delay)
>> +{
>> +	struct read_counters_work read_counters_work;
>> +	struct tegra_cpu_ctr c;
>> +	u32 delta_refcnt;
>> +	u32 delta_ccnt;
>> +	u32 rate_mhz;
>> +
>> +	/*
>> +	 * udelay() is required to reconstruct cpu frequency over an
>> +	 * observation window. Using workqueue to call udelay() with
>> +	 * interrupts enabled.
>> +	 */
>> +	read_counters_work.c.cpu = cpu;
>> +	read_counters_work.c.delay = delay;
>> +	INIT_WORK_ONSTACK(&read_counters_work.work, tegra_read_counters);
>> +	queue_work_on(cpu, read_counters_wq, &read_counters_work.work);
>> +	flush_work(&read_counters_work.work);
>> +	c = read_counters_work.c;
>> +
>> +	if (c.coreclk_cnt < c.last_coreclk_cnt)
>> +		delta_ccnt = c.coreclk_cnt + (MAX_CNT - c.last_coreclk_cnt);
>> +	else
>> +		delta_ccnt = c.coreclk_cnt - c.last_coreclk_cnt;
>> +	if (!delta_ccnt)
>> +		return 0;
>> +
>> +	/* ref clock is 32 bits */
>> +	if (c.refclk_cnt < c.last_refclk_cnt)
>> +		delta_refcnt = c.refclk_cnt + (MAX_CNT - c.last_refclk_cnt);
>> +	else
>> +		delta_refcnt = c.refclk_cnt - c.last_refclk_cnt;
>> +	if (!delta_refcnt) {
>> +		pr_debug("cpufreq: %d is idle, delta_refcnt: 0\n", cpu);
>> +		return 0;
>> +	}
>> +	rate_mhz = ((unsigned long)(delta_ccnt * REF_CLK_MHZ)) / delta_refcnt;
>> +
>> +	return (rate_mhz * KHZ); /* in KHz */
>> +}
>> +
>> +static unsigned int tegra194_get_speed(u32 cpu)
>> +{
>> +	return tegra194_get_speed_common(cpu, US_DELAY);
>> +}
>> +
>> +static unsigned int tegra194_fast_get_speed(u32 cpu)
>> +{
>> +	return tegra194_get_speed_common(cpu, US_DELAY_MIN);
>> +}
> 
> Personally, I would not bother with the above function as it is only
> used in one place.
> 
Kept the function for better readability. Ok, will open code it.

>> +
>> +static int tegra194_cpufreq_init(struct cpufreq_policy *policy)
>> +{
>> +	struct tegra194_cpufreq_data *data = cpufreq_get_driver_data();
>> +	int cl = get_cpu_cluster(policy->cpu);
>> +	u32 cpu;
>> +
>> +	if (cl >= data->num_clusters)
>> +		return -EINVAL;
>> +
>> +	policy->cur = tegra194_fast_get_speed(policy->cpu); /* boot freq */
>> +
>> +	/* set same policy for all cpus in a cluster */
>> +	for (cpu = (cl * 2); cpu < ((cl + 1) * 2); cpu++)
>> +		cpumask_set_cpu(cpu, policy->cpus);
>> +
>> +	policy->freq_table = data->tables[cl];
>> +	policy->cpuinfo.transition_latency = TEGRA_CPUFREQ_TRANSITION_LATENCY;
>> +
>> +	return 0;
>> +}
>> +
>> +static void set_cpu_ndiv(void *data)
>> +{
>> +	struct cpufreq_frequency_table *tbl = data;
>> +	u64 ndiv_val = (u64)tbl->driver_data;
>> +
>> +	asm volatile("msr s3_0_c15_c0_4, %0" : : "r" (ndiv_val));
>> +}
>> +
>> +static int tegra194_cpufreq_set_target(struct cpufreq_policy *policy,
>> +				       unsigned int index)
>> +{
>> +	struct cpufreq_frequency_table *tbl = policy->freq_table + index;
>> +
>> +	/*
>> +	 * Each core writes frequency in per core register. Then both cores
>> +	 * in a cluster run at same frequency which is the maximum frequency
>> +	 * request out of the values requested by both cores in that cluster.
>> +	 */
>> +	on_each_cpu_mask(policy->cpus, set_cpu_ndiv, tbl, true);
>> +
>> +	return 0;
>> +}
>> +
>> +static struct cpufreq_driver tegra194_cpufreq_driver = {
>> +	.name = "tegra194",
>> +	.flags = CPUFREQ_STICKY | CPUFREQ_CONST_LOOPS |
>> +		CPUFREQ_NEED_INITIAL_FREQ_CHECK,
>> +	.verify = cpufreq_generic_frequency_table_verify,
>> +	.target_index = tegra194_cpufreq_set_target,
>> +	.get = tegra194_get_speed,
>> +	.init = tegra194_cpufreq_init,
>> +	.attr = cpufreq_generic_attr,
>> +};
>> +
>> +static void tegra194_cpufreq_free_resources(void)
>> +{
>> +	destroy_workqueue(read_counters_wq);
>> +}
> 
> I would not bother with adding this function either.
> 
This function is used from remove call also.

>> +
>> +static struct cpufreq_frequency_table *
>> +init_freq_table(struct platform_device *pdev, struct tegra_bpmp *bpmp,
>> +		unsigned int cluster_id)
>> +{
>> +	struct cpufreq_frequency_table *freq_table;
>> +	struct mrq_cpu_ndiv_limits_response resp;
>> +	unsigned int num_freqs, ndiv, delta_ndiv;
>> +	struct mrq_cpu_ndiv_limits_request req;
>> +	struct tegra_bpmp_message msg;
>> +	u16 freq_table_step_size;
>> +	int err, index;
>> +
>> +	memset(&req, 0, sizeof(req));
>> +	req.cluster_id = cluster_id;
>> +
>> +	memset(&msg, 0, sizeof(msg));
>> +	msg.mrq = MRQ_CPU_NDIV_LIMITS;
>> +	msg.tx.data = &req;
>> +	msg.tx.size = sizeof(req);
>> +	msg.rx.data = &resp;
>> +	msg.rx.size = sizeof(resp);
>> +
>> +	err = tegra_bpmp_transfer(bpmp, &msg);
>> +	if (err)
>> +		return ERR_PTR(err);
>> +
>> +	/*
>> +	 * Make sure frequency table step is a multiple of mdiv to match
>> +	 * vhint table granularity.
>> +	 */
>> +	freq_table_step_size = resp.mdiv *
>> +			DIV_ROUND_UP(CPUFREQ_TBL_STEP_HZ, resp.ref_clk_hz);
>> +
>> +	dev_dbg(&pdev->dev, "cluster %d: frequency table step size: %d\n",
>> +		cluster_id, freq_table_step_size);
>> +
>> +	delta_ndiv = resp.ndiv_max - resp.ndiv_min;
>> +
>> +	if (unlikely(delta_ndiv == 0)) {
>> +		num_freqs = 1;
>> +	} else {
>> +		/* We store both ndiv_min and ndiv_max hence the +1 */
>> +		num_freqs = delta_ndiv / freq_table_step_size + 1;
>> +	}
>> +
>> +	num_freqs += (delta_ndiv % freq_table_step_size) ? 1 : 0;
>> +
>> +	freq_table = devm_kcalloc(&pdev->dev, num_freqs + 1,
>> +				  sizeof(*freq_table), GFP_KERNEL);
>> +	if (!freq_table)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	for (index = 0, ndiv = resp.ndiv_min;
>> +			ndiv < resp.ndiv_max;
>> +			index++, ndiv += freq_table_step_size) {
>> +		freq_table[index].driver_data = ndiv;
>> +		freq_table[index].frequency = map_ndiv_to_freq(&resp, ndiv);
>> +	}
>> +
>> +	freq_table[index].driver_data = resp.ndiv_max;
>> +	freq_table[index++].frequency = map_ndiv_to_freq(&resp, resp.ndiv_max);
>> +	freq_table[index].frequency = CPUFREQ_TABLE_END;
>> +
>> +	return freq_table;
>> +}
>> +
>> +static int tegra194_cpufreq_probe(struct platform_device *pdev)
>> +{
>> +	struct tegra194_cpufreq_data *data;
>> +	struct tegra_bpmp *bpmp;
>> +	int err, i;
>> +
>> +	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
>> +	if (!data)
>> +		return -ENOMEM;
>> +
>> +	data->num_clusters = MAX_CLUSTERS;
>> +	data->tables = devm_kcalloc(&pdev->dev, data->num_clusters,
>> +				    sizeof(*data->tables), GFP_KERNEL);
>> +	if (!data->tables)
>> +		return -ENOMEM;
>> +
>> +	platform_set_drvdata(pdev, data);
>> +
>> +	bpmp = tegra_bpmp_get(&pdev->dev);
>> +	if (IS_ERR(bpmp))
>> +		return PTR_ERR(bpmp);
>> +
>> +	read_counters_wq = alloc_workqueue("read_counters_wq", __WQ_LEGACY, 1);
>> +	if (!read_counters_wq) {
>> +		dev_err(&pdev->dev, "fail to create_workqueue\n");
>> +		err = -EINVAL;
>> +		goto put_bpmp;
>> +	}
>> +
>> +	for (i = 0; i < data->num_clusters; i++) {
>> +		data->tables[i] = init_freq_table(pdev, bpmp, i);
>> +		if (IS_ERR(data->tables[i])) {
>> +			err = PTR_ERR(data->tables[i]);
>> +			goto err_free_res;
>> +		}
>> +	}
>> +
>> +	tegra194_cpufreq_driver.driver_data = data;
>> +
>> +	err = cpufreq_register_driver(&tegra194_cpufreq_driver);
>> +	if (err)
>> +		goto err_free_res;
> 
> You don't need the above if statement now you added the below.
> 
Sorry, missed to remove this. Will wait if any other comments before 
re-spin.

>> +
>> +	if (!err)
>> +		goto put_bpmp;
>> +
>> +err_free_res:
>> +	tegra194_cpufreq_free_resources();
>> +put_bpmp:
>> +	tegra_bpmp_put(bpmp);
>> +	return err;
>> +}
>> +
>> +static int tegra194_cpufreq_remove(struct platform_device *pdev)
>> +{
>> +	cpufreq_unregister_driver(&tegra194_cpufreq_driver);
>> +	tegra194_cpufreq_free_resources();
>> +
>> +	return 0;
>> +}
>> +
>> +static const struct of_device_id tegra194_cpufreq_of_match[] = {
>> +	{ .compatible = "nvidia,tegra194-ccplex", },
>> +	{ /* sentinel */ }
>> +};
>> +MODULE_DEVICE_TABLE(of, tegra194_cpufreq_of_match);
>> +
>> +static struct platform_driver tegra194_ccplex_driver = {
>> +	.driver = {
>> +		.name = "tegra194-cpufreq",
>> +		.of_match_table = tegra194_cpufreq_of_match,
>> +	},
>> +	.probe = tegra194_cpufreq_probe,
>> +	.remove = tegra194_cpufreq_remove,
>> +};
>> +module_platform_driver(tegra194_ccplex_driver);
>> +
>> +MODULE_AUTHOR("Mikko Perttunen <mperttunen@nvidia.com>");
>> +MODULE_AUTHOR("Sumit Gupta <sumitg@nvidia.com>");
>> +MODULE_DESCRIPTION("NVIDIA Tegra194 cpufreq driver");
>> +MODULE_LICENSE("GPL v2");
>>
> 
> Cheers
> Jon
>