Message-ID: <CAPDyKFpwguzd_iy46mpPcwDs98bh1k_3fVNfe4UAjYYwNoBJPQ@mail.gmail.com>
Date:	Fri, 24 Oct 2014 11:53:05 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Grygorii Strashko <grygorii.strashko@...com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	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 23 October 2014 16:37, Grygorii Strashko <grygorii.strashko@...com> wrote:
> 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.

Correct.

This is also the key problem with your approach. You requires a
pm_runtime_get_sync() to trigger the runtime PM resume callbacks to be
invoked. That's a fragile design.

The solution that I propose is to "manually" enable your PM clks
during the probe sequence. We can do that as a part of pm_clk_add() or
we invoke pm_clk_resume() separately, but more important no matter of
CONFIG_PM_RUNTIME.

The driver could then be responsible to invoke pm_runtime_set_active()
to reflect that all runtime PM resources are enabled.

>
> 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 :..((

I agree to that this _has_ been an issue. It also remarkable that
people have been just accepting that for so long.

Now, we have added the pm_runtime_force_suspend|resume() helpers.
Those will help to solve these cases.

>
>
> 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;

This is wrong!

1) It will break the driver for !CONFIG_PM_RUNTIME.

2) It would also be broken for CONFIG_PM_RUNTIME for the scenario
where a bus also handles runtime PM resources.
Typically from the bus' ->probe() this is done:
pm_runtime_get_noresume()
pm_runtime_set_active()

As stated earlier, we shouldn't require the runtime PM resume callback
to be invoked just because a pm_runtime_get_sync(). It's fragile.

> +
> +       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.

pm_runtime_status_suspended() will always return false for !CONFIG_PM_RUNTIME.

There are no side effects as long as you have defined your runtime PM
callbacks within CONFIG_PM. SET_PM_RUNTIME_PM_OPS() also helps out
here.

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

If the runtime PM callbacks are invoked in atomic context, the driver
needs to tell the runtime PM core about it. That's done through,
pm_runtime_irq_safe(), which it doesn't.

>
> Oh, You definitely will be enjoyed ;)

Likely you to. :-)

Kind regards
Uffe
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