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

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Date:   Wed, 17 Oct 2018 16:32:33 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Taniya Das <tdas@...eaurora.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     Rajendra Nayak <rnayak@...eaurora.org>, devicetree@...r.kernel.org,
        robh@...nel.org, skannan@...eaurora.org,
        linux-arm-msm@...r.kernel.org, amit.kucheria@...aro.org,
        evgreen@...gle.com, Taniya Das <tdas@...eaurora.org>
Subject: Re: [PATCH 2/2] cpufreq: qcom-hw: Add support for QCOM cpufreq HW driver

Quoting Taniya Das (2018-10-11 04:36:01)
> --- a/drivers/cpufreq/Kconfig.arm
> +++ b/drivers/cpufreq/Kconfig.arm
> @@ -121,6 +121,17 @@ config ARM_QCOM_CPUFREQ_KRYO
> 
>           If in doubt, say N.
> 
> +config ARM_QCOM_CPUFREQ_HW
> +       bool "QCOM CPUFreq HW driver"

Is there any reason this can't be a module?

> +       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/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c
> new file mode 100644
> index 0000000..fe1c264
> --- /dev/null
> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
> @@ -0,0 +1,354 @@
> +// 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/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
> +
> +enum {
> +       REG_ENABLE,
> +       REG_LUT_TABLE,
> +       REG_PERF_STATE,
> +
> +       REG_ARRAY_SIZE,
> +};
> +
> +struct cpufreq_qcom {
> +       struct cpufreq_frequency_table *table;
> +       void __iomem *reg_bases[REG_ARRAY_SIZE];
> +       cpumask_t related_cpus;
> +       unsigned int max_cores;
> +       unsigned long xo_rate;
> +       unsigned long cpu_hw_rate;
> +};
> +
> +static const u16 cpufreq_qcom_std_offsets[REG_ARRAY_SIZE] = {

Is this going to change in the future?

> +       [REG_ENABLE]            = 0x0,
> +       [REG_LUT_TABLE]         = 0x110,
> +       [REG_PERF_STATE]        = 0x920,
> +};
> +
> +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->reg_bases[REG_PERF_STATE]);

Why can't we avoid the indirection here and store the perf_state pointer
in probe? Then we don't have to indirect through a table to perform the
register write.

> +
> +       return 0;
> +}
> +
[..]
> +static int qcom_resources_init(struct platform_device *pdev)
> +{
> +       struct device_node *cpu_np;
> +       struct of_phandle_args args;
> +       struct clk *clk;
> +       unsigned int cpu;
> +       unsigned long xo_rate, cpu_hw_rate;
> +       int ret;
> +
> +       clk = clk_get(&pdev->dev, "xo");
> +       if (IS_ERR(clk))
> +               return PTR_ERR(clk);
> +
> +       xo_rate = clk_get_rate(clk);
> +
> +       clk_put(clk);
> +
> +       clk = clk_get(&pdev->dev, "cpu_clk");

Sad that the name is cpu_clk, instead of something like 'backup' or
whatever the name really is in hardware.