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Date:	Thu, 23 Oct 2014 17:37:31 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Ulf Hansson <ulf.hansson@...aro.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	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

Hi Ulf,

On 10/23/2014 11:11 AM, Ulf Hansson wrote:
> 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().

Sorry, but some misunderstanding is here:
1) If some code call pm_runtime_set_active() it has to ensure
that all PM resources switched to ON state. All! So, it will 
be ok to call enable & get after that - these functions will only 
adjust counters.

2) if CONFIG_PM_RUNTIME=n the pm_runtime_set_active() will
be empty (see pm_runtime.h) and you can't relay on it.

3) if CONFIG_PM_RUNTIME=n the pm_runtime_enable/disable() will
be empty - and disable_depth == 1 all the time.

In my case, the combination of generic PD and PM clock framework
will do everything I need for both cases CONFIG_PM_RUNTIME=y/n.

PM domain attach_dev/detach_dev callbacks - will fill PM resources
and enable them if CONFIG_PM_RUNTIME=n.

if CONFIG_PM_RUNTIME - PM resources will be enabled/disabled
by Runtime PM through .start()/.stop() callbacks.

And seems suspend/resume will work too - can't try it now, but it
should work, because .start()/.stop() callbacks have to be called
from pm_genpd_suspend_noirq.


> 
> 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

It always was (and seems will) a big challenge to support both
CONFIG_PM_RUNTIME=y and system suspend in drivers ;), especially if driver was
initially created using Runtime PM centric approach.

But, for the case CONFIG_PM_RUNTIME + !CONFIG_PM_RUNTIME + suspend...
It will be painful :..((


For example your patches (may be I'm not fully understand your problem, 
so here are just comments to code):
patch 3:
  - I think you can do smth like this in probe 
        ret = pm_runtime_get_sync(&pdev->dev);
        if (ret < 0)
                goto err_m2m;
+       
+       if (!pm_runtime_enabled(dev)) {
+               gsc_runtime_resume(dev);
+       } 

 - and similar thing in remove, before pm_runtime_disable
 
patch 5 - pm_runtime_force_suspend/resume() will not take into
account or change Runtime PM state of the device if !CONFIG_PM_RUNTIME.
runtime_status == RPM_SUSPENDED always in this case!
So, there may be some side-effects.

patch 7 - you can't call clk_prepare/unprepare from Runtime PM
callbacks, because they aren't atomic

Oh, You definitely will be enjoyed ;)

regards,
-grygorii

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