linux-kernel - Re: [PATCH v3] cpufreq: brcmstb-cpufreq: CPUfreq driver for older Broadcom STB SoCs

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Date:   Mon, 28 Nov 2016 11:14:36 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Markus Mayer <code@...yer.net>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Power Management List <linux-pm@...r.kernel.org>,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Markus Mayer <mmayer@...adcom.com>
Subject: Re: [PATCH v3] cpufreq: brcmstb-cpufreq: CPUfreq driver for older Broadcom STB SoCs

On Tuesday, November 22, 2016 1:32:45 PM CET Markus Mayer wrote:
> From: Markus Mayer <mmayer@...adcom.com>
> 
> This CPUfreq driver provides basic frequency scaling for older Broadcom
> STB SoCs that do not use AVS firmware with DVFS support. There is no
> support for voltage scaling.
> 
> Signed-off-by: Markus Mayer <mmayer@...adcom.com>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

This causes multiple build errors in linux-next, please fix asap or
drop the patch again. My feeling is that it's probably too late to
fix it for v4.10, but that's up to Viresh and Rafael of course.

> +#define BRCMSTB_CPUFREQ_PREFIX	"brcmstb"
> +#define BRCMSTB_CPUFREQ_NAME	BRCMSTB_CPUFREQ_PREFIX "-cpufreq"
> +
> +/* We search for these compatible strings. */
> +#define BRCMSTB_DT_CPU_CLK_CTRL	"brcm,brcmstb-cpu-clk-div"
> +#define BRCMSTB_DT_MEMC_DDR	"brcm,brcmstb-memc-ddr"
> +#define BRCM_AVS_CPU_DATA	"brcm,avs-cpu-data-mem"
> +
> +/* We also need a few clocks in device tree. These are node names. */
> +#define BRCMSTB_CLK_MDIV_CH0	"cpu_mdiv_ch0"
> +#define BRCMSTB_CLK_NDIV_INT	"cpu_ndiv_int"
> +#define BRCMSTB_CLK_SW_SCB	"sw_scb"

Not critical but the use of those macros obfuscates the DT interfaces
here and made it harder to analyse what was going on.

Also, a couple of them are lacking a DT binding.

> +static int get_frequencies(const struct cpufreq_policy *policy,
> +			   unsigned int *vco_freq, unsigned int *cpu_freq,
> +			   unsigned int *scb_freq)
> +{
> +	struct clk *cpu_ndiv_int, *sw_scb;
> +
> +	cpu_ndiv_int = __clk_lookup(BRCMSTB_CLK_NDIV_INT);
> +	if (!cpu_ndiv_int)
> +		return -ENODEV;
> +
> +	sw_scb = __clk_lookup(BRCMSTB_CLK_SW_SCB);
> +	if (!sw_scb)
> +		return -ENODEV;
> +
> +	/* return frequencies in kHz */
> +	*vco_freq = clk_get_rate(cpu_ndiv_int) / 1000;
> +	*cpu_freq = clk_get_rate(policy->clk) / 1000;
> +	*scb_freq = clk_get_rate(sw_scb) / 1000;
> +
> +	return 0;
> +}

You really can't do this: 

../drivers/cpufreq/brcmstb-cpufreq.c: In function 'get_frequencies':
../drivers/cpufreq/brcmstb-cpufreq.c:71:17: error: implicit declaration of function '__clk_lookup';did you mean 'key_lookup'? [-Werror=implicit-function-declaration]
  cpu_ndiv_int = __clk_lookup(BRCMSTB_CLK_NDIV_INT);
                 ^~~~~~~~~~~~

__clk_lookup is an internal API for the clk providers.

In particular, relying on undocumented internal names of the
clk provider in a device driver is inappropriate.

> +static const struct of_device_id brcmstb_cpufreq_match[] = {
> +	{ .compatible = BRCMSTB_DT_CPU_CLK_CTRL },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(platform, brcmstb_cpufreq_match);

This is a simple typo, also causing the build to fail:

    FATAL: drivers/cpufreq/brcmstb-cpufreq: sizeof(struct platform_device_id)=24 is not a modulo of the size of section __mod_platform__<identifier>_device_table=392.

	Arnd