Re: [PATCH v7 2/2] cpufreq: qcom-hw: Add support for QCOM cpufreq HW driver

[Matthias Kaehlcke <mka@chromium.org>]

On Sun, Sep 23, 2018 at 03:10:55PM +0530, Taniya Das wrote:
> Hello Matthias,
> 
> Thanks for your review comments.
> 
> On 8/29/2018 11:31 PM, Matthias Kaehlcke wrote:
> > Hi Taniya,
> > 
> > On Tue, Jul 24, 2018 at 04:12:50PM +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@codeaurora.org>
> > > Signed-off-by: Taniya Das <tdas@codeaurora.org>
> > > ---
> > >   drivers/cpufreq/Kconfig.arm       |  11 ++
> > >   drivers/cpufreq/Makefile          |   1 +
> > >   drivers/cpufreq/qcom-cpufreq-hw.c | 348 ++++++++++++++++++++++++++++++++++++++
> > >   3 files changed, 360 insertions(+)
> > >   create mode 100644 drivers/cpufreq/qcom-cpufreq-hw.c
> > > 
> > > diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> > > index 0cd8eb7..93a9d72 100644
> > > --- a/drivers/cpufreq/Kconfig.arm
> > > +++ b/drivers/cpufreq/Kconfig.arm
> > > @@ -298,3 +298,14 @@ config ARM_PXA2xx_CPUFREQ
> > >   	  This add the CPUFreq driver support for Intel PXA2xx SOCs.
> > > 
> > >   	  If in doubt, say N.
> > > +
> > > +config ARM_QCOM_CPUFREQ_HW
> > > +	bool "QCOM CPUFreq HW driver"
> > > +	depends on ARCH_QCOM
> > > +	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.
> > > diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> > > index c1ffeab..ca48a1d 100644
> > > --- a/drivers/cpufreq/Makefile
> > > +++ b/drivers/cpufreq/Makefile
> > > @@ -85,6 +85,7 @@ obj-$(CONFIG_ARM_TEGRA124_CPUFREQ)	+= tegra124-cpufreq.o
> > >   obj-$(CONFIG_ARM_TEGRA186_CPUFREQ)	+= tegra186-cpufreq.o
> > >   obj-$(CONFIG_ARM_TI_CPUFREQ)		+= ti-cpufreq.o
> > >   obj-$(CONFIG_ARM_VEXPRESS_SPC_CPUFREQ)	+= vexpress-spc-cpufreq.o
> > > +obj-$(CONFIG_ARM_QCOM_CPUFREQ_HW)	+= qcom-cpufreq-hw.o
> > > 
> > > 
> > >   ##################################################################################
> > > diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c
> > > new file mode 100644
> > > index 0000000..ea8f7d1
> > > --- /dev/null
> > > +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
> > > @@ -0,0 +1,348 @@
> > > +// 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 INIT_RATE			300000000UL
> > > +#define LUT_MAX_ENTRIES			40U
> > > +#define CORE_COUNT_VAL(val)		(((val) & (GENMASK(18, 16))) >> 16)
> > > +#define LUT_ROW_SIZE			32
> > > +
> > > +enum {
> > > +	REG_ENABLE,
> > > +	REG_LUT_TABLE,
> > > +	REG_PERF_STATE,
> > > +
> > > +	REG_ARRAY_SIZE,
> > > +};
> > > +
> > > +struct cpufreq_qcom {
> > > +	struct cpufreq_frequency_table *table;
> > > +	struct device *dev;
> > 
> > 'dev' is not used and can be removed.
> > 
> 
> Thanks, would remove in the next patch.
> 
> > > ...
> > > 
> > > +static int qcom_cpu_resources_init(struct platform_device *pdev,
> > > +				   struct device_node *np, unsigned int cpu,
> > > +				   unsigned long xo_rate)
> > > +{
> > > +	struct cpufreq_qcom *c;
> > > +	struct resource res;
> > > +	struct device *dev = &pdev->dev;
> > > +	const u16 *offsets;
> > > +	int ret, i, cpu_first, cpu_r;
> > > +	void __iomem *base;
> > > +
> > > +	if (qcom_freq_domain_map[cpu])
> > > +		return 0;
> > > +
> > > +	c = devm_kzalloc(dev, sizeof(*c), GFP_KERNEL);
> > > +	if (!c)
> > > +		return -ENOMEM;
> > > +
> > > +	offsets = of_device_get_match_data(&pdev->dev);
> > > +	if (!offsets)
> > > +		return -EINVAL;
> > > +
> > > +	if (of_address_to_resource(np, 0, &res))
> > > +		return -ENOMEM;
> > > +
> > > +	base = devm_ioremap_resource(dev, &res);
> > > +	if (!base)
> > > +		return -ENOMEM;
> > > +
> > > +	for (i = REG_ENABLE; i < REG_ARRAY_SIZE; i++)
> > > +		c->reg_bases[i] = base + offsets[i];
> > > +
> > > +	/* HW should be in enabled state to proceed */
> > > +	if (!(readl_relaxed(c->reg_bases[REG_ENABLE]) & 0x1)) {
> > > +		dev_err(dev, "%s cpufreq hardware not enabled\n", np->name);
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	ret = qcom_get_related_cpus(np, &c->related_cpus);
> > > +	if (ret) {
> > > +		dev_err(dev, "%s failed to get related CPUs\n", np->name);
> > > +		return ret;
> > > +	}
> > > +
> > > +	c->max_cores = cpumask_weight(&c->related_cpus);
> > > +	if (!c->max_cores)
> > > +		return -ENOENT;
> > > +
> > > +	c->xo_rate = xo_rate;
> > > +
> > > +	ret = qcom_cpufreq_hw_read_lut(pdev, c);
> > > +	if (ret) {
> > > +		dev_err(dev, "%s failed to read LUT\n", np->name);
> > > +		return ret;
> > > +	}
> > > +
> > > +	qcom_freq_domain_map[cpu] = c;
> > > +
> > > +	/* Related CPUs */
> > > +	cpu_first = cpumask_first(&c->related_cpus);
> > > +
> > > +	for_each_cpu(cpu_r, &c->related_cpus) {
> > > +		if (cpu_r != cpu_first)
> > > +			qcom_freq_domain_map[cpu_r] =
> > > +				qcom_freq_domain_map[cpu_first];
> > > +	}
> > 
> > The above ten lines could be simplified to:
> > 
> > 	for_each_cpu(cpu_r, &c->related_cpus)
> > 		qcom_freq_domain_map[cpu_r] = c;
> > 
> 
> Would clean it up in the next patch.
> 
> > > ...
> > > 
> > > +static int __init qcom_cpufreq_hw_init(void)
> > > +{
> > > +	return platform_driver_register(&qcom_cpufreq_hw_driver);
> > > +}
> > > +subsys_initcall(qcom_cpufreq_hw_init);
> > 
> > Is subsys_initcall used for a particular reason? It will cause
> > problems when registering cooling devices, since the thermal device
> > class is initialized through an fs_initcall, which are executed
> > later.
> > 
> > Most cpufreq drivers use module_init, device_initcall or
> > late_initcall, can't this driver use one of those?
> > 
> 
> We want the CPU to be scaling to the highest frequency at the
> earliest.

I guess you also want thermal management for the CPU. With the
subsys_initcall registration of cooling devices fails, as mentioned in
my earlier comment. Do you plan to defer the registration of cooling
devices?

Cheers

Matthias