linux-kernel - Re: [PATCH v3 2/2] cpufreq: tegra: Re-model Tegra cpufreq driver

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Date:	Thu, 05 Dec 2013 16:04:33 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Bill Huang <bilhuang@...dia.com>, rjw@...ysocki.net,
	viresh.kumar@...aro.org, thierry.reding@...il.com
CC:	linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v3 2/2] cpufreq: tegra: Re-model Tegra cpufreq driver

On 12/05/2013 12:44 AM, Bill Huang wrote:
> Re-model Tegra cpufreq driver to support all Tegra series of SoCs.
> 
> * Make tegra-cpufreq.c a generic Tegra cpufreq driver.
> * Move Tegra20 specific codes into tegra20-cpufreq.c.
> * Bind Tegra cpufreq dirver with a fake device so defer probe would work
>   when we're going to get regulator in the driver to support voltage
>   scaling (DVFS).

> diff --git a/drivers/cpufreq/tegra-cpufreq.c b/drivers/cpufreq/tegra-cpufreq.c

> @@ -91,14 +40,10 @@ static int tegra_update_cpu_speed(struct cpufreq_policy *policy,
...
> +	if (soc_config->vote_emc_on_cpu_rate)
> +		soc_config->vote_emc_on_cpu_rate(rate);
> +
> +	ret = soc_config->cpu_clk_set_rate(rate * 1000);
>  	if (ret)
>  		pr_err("cpu-tegra: Failed to set cpu frequency to %lu kHz\n",
>  			rate);

Is there any/much shared code left in this file after this patch? It
seems like all this file does now is make each cpufreq callback function
call soc_config->the_same_function_name(). If so, wouldn't it be better
to simply implement completely separate tegar20-cpufreq and
tegra30-cpufreq drivers, and register them each directly with the
cpufreq core, to avoid this file doing all the indirection?


> -int __init tegra_cpufreq_init(void)
> +static struct {
> +	char *compat;
> +	int (*init)(struct tegra_cpufreq_data *,
> +			const struct tegra_cpufreq_config **);
> +} tegra_init_funcs[] = {
> +	{ "nvidia,tegra20", tegra20_cpufreq_init },
> +};
> +
> +static int tegra_cpufreq_probe(struct platform_device *pdev)
...
> +	for (i = 0; i < ARRAY_SIZE(tegra_init_funcs); i++) {
> +		if (of_machine_is_compatible(tegra_init_funcs[i].compat)) {
> +			ret = tegra_init_funcs[i].init(tegra_data, &soc_config);
> +			if (!ret)
> +				break;
> +			else
> +				goto out;
> +		}
>  	}
> +	if (i == ARRAY_SIZE(tegra_init_funcs))
> +		goto out;

I think there are better ways of doing this than open-coding it. Perhaps
of_match_device() or the platform-driver equivalent could be made to work?

> +int __init tegra_cpufreq_init(void)
> +{
> +	struct platform_device_info devinfo = { .name = "tegra-cpufreq", };
> +
> +	platform_device_register_full(&devinfo);
> +
> +	return 0;
>  }
>  EXPORT_SYMBOL(tegra_cpufreq_init);

Perhaps instead of hard-coding the name "tegra-cpufreq" here, you could
dynamically construct the device name based on the DT's root compatible
value, register "${root_compatible}-cpufreq", e.g.
"nvidia,tegra20-cpufreq" or "nvidia,tegra30-cpufreq". That would allow
the kernel's standard device/driver matching mechanism to pick the
correct driver to instantiate. Perhaps you could even dynamically
register an OF device so that you can use of_match_device() in probe, if
there's some advantage of having a single driver that supports N chips.
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