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Date: Wed, 23 Jul 2014 15:35:46 +0300
From: Tuomas Tynkkynen <ttynkkynen@...dia.com>
To: Thierry Reding <thierry.reding@...il.com>
CC: "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
Stephen Warren <swarren@...dotorg.org>,
Peter De Schrijver <pdeschrijver@...dia.com>,
Prashant Gaikwad <pgaikwad@...dia.com>,
Mike Turquette <mturquette@...aro.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Viresh Kumar <viresh.kumar@...aro.org>,
Paul Walmsley <pwalmsley@...dia.com>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 14/16] cpufreq: Add cpufreq driver for Tegra124
On 23/07/14 10:09, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Mon, Jul 21, 2014 at 06:39:00PM +0300, Tuomas Tynkkynen wrote:
> [...]
>> diff --git a/drivers/cpufreq/tegra124-cpufreq.c b/drivers/cpufreq/tegra124-cpufreq.c
> [...]
>> +static int tegra124_cpu_switch_to_dfll(void)
>> +{
>> + struct clk *original_cpu_clk_parent;
>
> Maybe just "parent"?
>
>> + unsigned long rate;
>> + struct dev_pm_opp *opp;
>> + int ret;
>> +
>> + rate = clk_get_rate(cpu_clk);
>> + opp = dev_pm_opp_find_freq_ceil(cpu_dev, &rate);
>> + if (IS_ERR(opp))
>> + return PTR_ERR(opp);
>> +
>> + ret = clk_set_rate(dfll_clk, rate);
>> + if (ret)
>> + return ret;
>> +
>> + original_cpu_clk_parent = clk_get_parent(cpu_clk);
>> + clk_set_parent(cpu_clk, pllp_clk);
>> + if (ret)
>> + return ret;
>> +
>> + ret = clk_prepare_enable(dfll_clk);
>> + if (ret)
>> + goto out_switch_to_original_parent;
>
> This could simply be "out" or "err" or anything else shorter than the
> above.
>
>> +
>> + clk_set_parent(cpu_clk, dfll_clk);
>> +
>> + return 0;
>> +
>> +out_switch_to_original_parent:
>> + clk_set_parent(cpu_clk, original_cpu_clk_parent);
>> +
>> + return ret;
>> +}
>> +
>> +static struct platform_device_info cpufreq_cpu0_devinfo = {
>> + .name = "cpufreq-cpu0",
>> +};
>> +
>> +static int tegra124_cpufreq_probe(struct platform_device *pdev)
>> +{
>> + int ret;
>> +
>> + cpu_dev = get_cpu_device(0);
>> + if (!cpu_dev)
>> + return -ENODEV;
>> +
>> + cpu_clk = of_clk_get_by_name(cpu_dev->of_node, "cpu_g");
>> + if (IS_ERR(cpu_clk))
>> + return PTR_ERR(cpu_clk);
>> +
>> + dfll_clk = of_clk_get_by_name(cpu_dev->of_node, "dfll");
>> + if (IS_ERR(dfll_clk)) {
>> + ret = PTR_ERR(dfll_clk);
>> + goto out_put_cpu_clk;
>> + }
>> +
>> + pllx_clk = of_clk_get_by_name(cpu_dev->of_node, "pll_x");
>> + if (IS_ERR(pllx_clk)) {
>> + ret = PTR_ERR(pllx_clk);
>> + goto out_put_dfll_clk;
>> + }
>> +
>> + pllp_clk = of_clk_get_by_name(cpu_dev->of_node, "pll_p");
>> + if (IS_ERR(pllp_clk)) {
>> + ret = PTR_ERR(pllp_clk);
>> + goto out_put_pllx_clk;
>> + }
>
> Can the above not be devm_clk_get(cpu_dev, "...") so that you can remove
> all the clk_put() calls in the cleanup code below?
That would allocate the clks under the cpu_dev's devres list, i.e. all the
clk_puts wouldn't happen when the cpufreq driver goes away, but only when
cpu_dev itself goes away.
>
>> +
>> + ret = dev_pm_opp_init_cpufreq_table(cpu_dev, &freq_table);
>> + if (ret)
>> + goto out_put_pllp_clk;
>> +
>> + ret = tegra124_cpu_switch_to_dfll();
>> + if (ret)
>> + goto out_free_table;
>> +
>> + platform_device_register_full(&cpufreq_cpu0_devinfo);
>
> Should the cpufreq_cpu0_devinfo device perhaps be a child of pdev?
Yeah, I suppose it should.
>> +
>> + return 0;
>> +
>> +out_free_table:
>> + dev_pm_opp_free_cpufreq_table(cpu_dev, &freq_table);
>> +out_put_pllp_clk:
>> + clk_put(pllp_clk);
>> +out_put_pllx_clk:
>> + clk_put(pllx_clk);
>> +out_put_dfll_clk:
>> + clk_put(dfll_clk);
>> +out_put_cpu_clk:
>> + clk_put(cpu_clk);
>> +
>> + return ret;
>> +}
>> +
>> +static struct platform_driver tegra124_cpufreq_platdrv = {
>> + .driver = {
>> + .name = "cpufreq-tegra124",
>> + .owner = THIS_MODULE,
>> + },
>> + .probe = tegra124_cpufreq_probe,
>
> Note that simply leaving out .remove() here doesn't guarantee that the
> driver won't be unloaded. Also building it into the kernel doesn't
> prevent that. You can still unbind the driver via sysfs. So you'd need
> to add a .suppress_bind_attrs = true above.
I hadn't heard about suppress_bind_attrs before, it indeed sounds useful.
> But is there even a reason why we need that? Couldn't we make the
> driver's .remove() undo what .probe() did so that the driver can be
> unloaded?
I guess that could be done, though to fully undo everything the regulator
voltage would also need to be saved/restored.
> Otherwise it probably makes more sense not to use a driver (and dummy
> device) at all as Viresh already mentioned.
>
The dummy platform device is only required for probe deferral, if that
could be solved in a different way then yes.
>> +};
>> +
>> +static const struct of_device_id soc_of_matches[] = {
>> + { .compatible = "nvidia,tegra124", },
>> + {}
>> +};
>> +
>> +static int __init tegra_cpufreq_init(void)
>> +{
>> + int ret;
>> + struct platform_device *pdev;
>> +
>> + if (!of_find_matching_node(NULL, soc_of_matches))
>> + return -ENODEV;
>
> I think this could be of_machine_is_compatible() since there's only a
> single entry in the match table. If there's a good chance that we may
> end up with more entries, perhaps now would be a good time to add an
> of_match_machine() function?
I think this driver should work on Tegra132 without modifications.
of_match_machine() does sound useful for some of the other cpufreq
drivers as well and likely for your soc_is_tegra() from the PMC
series as well.
>
>> +
>> + ret = platform_driver_register(&tegra124_cpufreq_platdrv);
>> + if (ret)
>> + return ret;
>> +
>> + pdev = platform_device_register_simple("cpufreq-tegra124", -1, NULL, 0);
>> + if (IS_ERR(pdev)) {
>> + platform_driver_unregister(&tegra124_cpufreq_platdrv);
>> + return PTR_ERR(pdev);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +MODULE_AUTHOR("Tuomas Tynkkynen <ttynkkynen@...dia.com>");
>> +MODULE_DESCRIPTION("cpufreq driver for nVIDIA Tegra124");
>
> We use "NVIDIA" everywhere nowadays.
>
>> +MODULE_LICENSE("GPLv2");
>
> The correct license string is "GPL v2".
>
>> +module_init(tegra_cpufreq_init);
>
> The placement of this is unusual. It should go immediately below the
> tegra_cpufreq_init() function.
>
Ok.
Thanks,
Tuomas
--
nvpublic
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