Re: [PATCH v10 2/2] cpufreq: qcom-hw: Add support for QCOM cpufreq HW driver

[Matthias Kaehlcke]

On Wed, Nov 21, 2018 at 04:12:47PM +0530, Taniya Das wrote:
> The CPUfreq HW present in some QCOM chipsets offloads the steps necessary
> for changing the frequency of CPUs. The driver implements the cpufreq
> driver interface for this hardware engine.
> 
> Signed-off-by: Saravana Kannan <skannan@xxxxxxxxxxxxxx>
> Signed-off-by: Taniya Das <tdas@xxxxxxxxxxxxxx>
> ---
>  drivers/cpufreq/Kconfig.arm       |  11 ++
>  drivers/cpufreq/Makefile          |   1 +
>  drivers/cpufreq/qcom-cpufreq-hw.c | 346 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 358 insertions(+)
>  create mode 100644 drivers/cpufreq/qcom-cpufreq-hw.c
> 
> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> index 4e1131e..688f102 100644
> --- a/drivers/cpufreq/Kconfig.arm
> +++ b/drivers/cpufreq/Kconfig.arm
> @@ -114,6 +114,17 @@ config ARM_QCOM_CPUFREQ_KRYO
> 
>  	  If in doubt, say N.
> 
> +config ARM_QCOM_CPUFREQ_HW
> +	tristate "QCOM CPUFreq HW driver"
> +	depends on ARCH_QCOM || COMPILE_TEST
> +	help
> +	  Support for the CPUFreq HW driver.
> +	  Some QCOM chipsets have a HW engine to offload the steps
> +	  necessary for changing the frequency of the CPUs. Firmware loaded
> +	  in this engine exposes a programming interface to the OS.
> +	  The driver implements the cpufreq interface for this HW engine.
> +	  Say Y if you want to support CPUFreq HW.
> +
>  config ARM_S3C_CPUFREQ
>  	bool
>  	help
> diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> index d5ee456..789b2e0 100644
> --- a/drivers/cpufreq/Makefile
> +++ b/drivers/cpufreq/Makefile
> @@ -62,6 +62,7 @@ obj-$(CONFIG_ARM_OMAP2PLUS_CPUFREQ)	+= omap-cpufreq.o
>  obj-$(CONFIG_ARM_PXA2xx_CPUFREQ)	+= pxa2xx-cpufreq.o
>  obj-$(CONFIG_PXA3xx)			+= pxa3xx-cpufreq.o
>  obj-$(CONFIG_ARM_QCOM_CPUFREQ_KRYO)	+= qcom-cpufreq-kryo.o
> +obj-$(CONFIG_ARM_QCOM_CPUFREQ_HW)	+= qcom-cpufreq-hw.o
>  obj-$(CONFIG_ARM_S3C2410_CPUFREQ)	+= s3c2410-cpufreq.o
>  obj-$(CONFIG_ARM_S3C2412_CPUFREQ)	+= s3c2412-cpufreq.o
>  obj-$(CONFIG_ARM_S3C2416_CPUFREQ)	+= s3c2416-cpufreq.o
> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c
> new file mode 100644
> index 0000000..6390e85
> --- /dev/null
> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
> @@ -0,0 +1,346 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2018, The Linux Foundation. All rights reserved.
> + */
> +
> +#include <linux/cpufreq.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of_address.h>
> +#include <linux/of_platform.h>
> +
> +#define LUT_MAX_ENTRIES			40U
> +#define CORE_COUNT_VAL(val)		(((val) & (GENMASK(18, 16))) >> 16)
> +#define LUT_ROW_SIZE			32
> +#define CLK_HW_DIV			2
> +
> +/* Register offsets */
> +#define REG_ENABLE			0x0
> +#define REG_LUT_TABLE			0x110
> +#define REG_PERF_STATE			0x920
> +
> +struct cpufreq_qcom {
> +	struct cpufreq_frequency_table *table;
> +	void __iomem *perf_base;
> +	cpumask_t related_cpus;
> +	unsigned int max_cores;
> +	unsigned long xo_rate;
> +	unsigned long cpu_hw_rate;
> +};
> +
> +static struct cpufreq_qcom *qcom_freq_domain_map[NR_CPUS];
> +
> +static int
> +qcom_cpufreq_hw_target_index(struct cpufreq_policy *policy,
> +			     unsigned int index)
> +{
> +	struct cpufreq_qcom *c = policy->driver_data;
> +
> +	writel_relaxed(index, c->perf_base);
> +
> +	return 0;
> +}
> +
> +static unsigned int qcom_cpufreq_hw_get(unsigned int cpu)
> +{
> +	struct cpufreq_qcom *c;
> +	struct cpufreq_policy *policy;
> +	unsigned int index;
> +
> +	policy = cpufreq_cpu_get_raw(cpu);
> +	if (!policy)
> +		return 0;
> +
> +	c = policy->driver_data;
> +
> +	index = readl_relaxed(c->perf_base);
> +	index = min(index, LUT_MAX_ENTRIES - 1);
> +
> +	return policy->freq_table[index].frequency;
> +}
> +
> +static unsigned int
> +qcom_cpufreq_hw_fast_switch(struct cpufreq_policy *policy,
> +			    unsigned int target_freq)
> +{
> +	struct cpufreq_qcom *c = policy->driver_data;
> +	int index;
> +
> +	index = policy->cached_resolved_idx;
> +	if (index < 0)
> +		return 0;
> +
> +	writel_relaxed(index, c->perf_base);
> +
> +	return policy->freq_table[index].frequency;
> +}
> +
> +static int qcom_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
> +{
> +	struct cpufreq_qcom *c;
> +
> +	c = qcom_freq_domain_map[policy->cpu];
> +	if (!c) {
> +		pr_err("No scaling support for CPU%d\n", policy->cpu);
> +		return -ENODEV;
> +	}
> +
> +	cpumask_copy(policy->cpus, &c->related_cpus);
> +
> +	policy->fast_switch_possible = true;
> +	policy->freq_table = c->table;
> +	policy->driver_data = c;
> +
> +	return 0;
> +}
> +
> +static struct freq_attr *qcom_cpufreq_hw_attr[] = {
> +	&cpufreq_freq_attr_scaling_available_freqs,
> +	&cpufreq_freq_attr_scaling_boost_freqs,
> +	NULL
> +};
> +
> +static struct cpufreq_driver cpufreq_qcom_hw_driver = {
> +	.flags		= CPUFREQ_STICKY | CPUFREQ_NEED_INITIAL_FREQ_CHECK |
> +			  CPUFREQ_HAVE_GOVERNOR_PER_POLICY,
> +	.verify		= cpufreq_generic_frequency_table_verify,
> +	.target_index	= qcom_cpufreq_hw_target_index,
> +	.get		= qcom_cpufreq_hw_get,
> +	.init		= qcom_cpufreq_hw_cpu_init,
> +	.fast_switch    = qcom_cpufreq_hw_fast_switch,
> +	.name		= "qcom-cpufreq-hw",
> +	.attr		= qcom_cpufreq_hw_attr,
> +	.boost_enabled	= true,

I have no real expertise with cpufreq boost, but after reading a bit
through cpufreq code this seems wrong. Boost is enabled statically,
however the driver has neither a ->set_boost function nor does it call
cpufreq_enable_boost_support() which would use a default
implementation for ->set_boost. As a result boost support is
effectively disabled:

static bool cpufreq_boost_supported(void)
{
        return likely(cpufreq_driver) && cpufreq_driver->set_boost;
}

The driver should probably do the same as cpufreq-dt.c and call
cpufreq_enable_boost_support() if boost frequencies are available,
instead of 'enabling' boost statically.

Thanks

Matthias