linux-kernel - Re: [PATCH v2 2/3] ARM: keystone: pm: switch to use generic pm domains

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Message-ID: <CAPDyKFrVCczc+fSy1ax4XinhB4SMfZZWP=d4QdY5Lv4zjOrHPA@mail.gmail.com>
Date:	Thu, 23 Oct 2014 10:11:00 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Grygorii Strashko <grygorii.strashko@...com>,
	Santosh Shilimkar <santosh.shilimkar@...il.com>,
	ssantosh@...nel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...aro.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] ARM: keystone: pm: switch to use generic pm domains

On 22 October 2014 17:44, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Wed, Oct 22, 2014 at 5:28 PM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> On 22 October 2014 17:09, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>>> On Wed, Oct 22, 2014 at 5:01 PM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>>>>>> +void keystone_pm_domain_attach_dev(struct device *dev)
>>>>>>>   {
>>>>>>> +    struct clk *clk;
>>>>>>>       int ret;
>>>>>>> +    int i = 0;
>>>>>>>
>>>>>>>       dev_dbg(dev, "%s\n", __func__);
>>>>>>>
>>>>>>> -    ret = pm_generic_runtime_suspend(dev);
>>>>>>> -    if (ret)
>>>>>>> -        return ret;
>>>>>>> -
>>>>>>> -    ret = pm_clk_suspend(dev);
>>>>>>> +    ret = pm_clk_create(dev);
>>>>>>>       if (ret) {
>>>>>>> -        pm_generic_runtime_resume(dev);
>>>>>>> -        return ret;
>>>>>>> +        dev_err(dev, "pm_clk_create failed %d\n", ret);
>>>>>>> +        return;
>>>>>>> +    };
>>>>>>> +
>>>>>>> +    while ((clk = of_clk_get(dev->of_node, i++)) && !IS_ERR(clk)) {
>>>>>>> +        ret = pm_clk_add_clk(dev, clk);
>>>>>>> +        if (ret) {
>>>>>>> +            dev_err(dev, "pm_clk_add_clk failed %d\n", ret);
>>>>>>> +            goto clk_err;
>>>>>>> +        };
>>>>>>>       }
>>>>>>>
>>>>>>> -    return 0;
>>>>>>> +    if (!IS_ENABLED(CONFIG_PM_RUNTIME)) {
>>>>>> Can we not okkup two seperate callbacks instead of above check ?
>>>>>> I don't like this CONFIG check here. Its slightly better version of
>>>>>> ifdef in middle of the code.
>>>>>
>>>>> I've found more-less similar comment on patch
>>>>> "Re: [PATCH v3 1/3] power-domain: add power domain drivers for Rockchip platform"
>>>>> https://lkml.org/lkml/2014/10/17/257
>>>>>
>>>>> So, Would you like me to create patch which will enable clocks in pm_clk_add/_clk()
>>>>> in case !IS_ENABLED(CONFIG_PM_RUNTIME)
>>>>
>>>> I am wondering whether we actually should/could do this, no matter of
>>>> CONFIG_PM_RUNTIME.
>>>>
>>>> Typically, for configurations that uses CONFIG_PM_RUNTIME, the PM
>>>> clocks through pm_clk_suspend(), will be gated once the device becomes
>>>> runtime PM suspended. Right?
>>>
>>> Doing it unconditionally means we'll have lots of unneeded clocks running
>>> for a short while.
>
>> As long as the pm_clk_add() is being invoked from the ->attach_dev()
>> callback, we are in the probe path. Certainly we would like to have
>> clocks enabled while probing, don't you think?
>>
>> If we wouldn't enable the clocks for CONFIG_PM_RUNTIME, when will
>> those be enabled?
>
> They will be enabled when the driver does
>
>         pm_runtime_enable(dev);
>         pm_runtime_get_sync(dev);
>
> in its .probe() method.

No! This doesn't work for drivers which have used
pm_runtime_set_active() prior pm_runtime_enable().

That should also be a common good practice for most drivers, otherwise
they wouldn’t work unless CONFIG_PM_RUNTIME is enabled.

Please have a look at the following patchset, which is fixing up one
driver to behave better.
http://marc.info/?l=linux-pm&m=141327095713390&w=2

Kind regards
Uffe
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