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

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Date:	Sat, 25 Oct 2014 12:45:23 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Grygorii Strashko <grygorii.strashko@...com>,
	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 24 October 2014 18:39, Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> On Fri, Oct 24, 2014 at 11:53:05AM +0200, Ulf Hansson wrote:
>> 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.
>
> Why is this fragile design? Having pm_runtime_get_sync() result in
> resuming the device (and in turn the PM domain it is in) if device is
> suspended is the proper behavior, no?

It's fragile, because the device may very well be "runtime PM active"
at the point when we invoke pm_runtime_get_sync(). Thus the runtime PM
resume callback isn't invoked, which is a requirement for these cases
to work.

Kind regards
Uffe
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