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

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Date:   Mon, 28 Nov 2016 21:58:53 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Markus Mayer <markus.mayer@...adcom.com>
Cc:     Markus Mayer <code@...yer.net>,
        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>
Subject: Re: [PATCH v3] cpufreq: brcmstb-cpufreq: CPUfreq driver for older Broadcom STB SoCs

On Monday, November 28, 2016 9:12:05 AM CET Markus Mayer wrote:
> >> +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.
> 
> What compiler are you using? I didn't get any warnings. Otherwise I
> would have known right away that something isn't right.

This is a randconfig build with CONFIG_COMMON_CLK=n. There is a different
problem with COMMON_CLK=y and the cpufreq driver as a loadable module,
where the symbol causes a link error.

I did not get any warnings either, these are both hard errors.

> >> +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.
> 
> What is the typo, if I may ask. Again strange, since the build doesn't
> fail for me. What was the configuration you used?

MODULE_DEVICE_TABLE() is only used when building a loadable module,
e.g. in allmodconfig.

MODULE_DEVICE_TABLE(platform, ...) is for 'struct platform_device_id'.
You need to use MODULE_DEVICE_TABLE(of, ...) for 'struct of_device_id'.

	Arnd