linux-kernel - Re: [RFC 1/2] PM / suspend: Add platform_suspend_target

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Message-ID: <d8c15114-636d-79bb-883e-d2d4439f755d@gmail.com>
Date:   Sun, 16 Jul 2017 08:35:59 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Pavel Machek <pavel@....cz>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-pm <linux-pm@...r.kernel.org>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        JB <jb_lescher@...madesigns.com>, Mason <slash.tmp@...e.fr>,
        Kevin Hilman <khilman@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 1/2] PM / suspend: Add platform_suspend_target_state()



On 07/16/2017 06:41 AM, Alexandre Belloni wrote:
> On 06/07/2017 at 05:18:19 +0200, Pavel Machek wrote:
>> On Sat 2017-07-15 20:33:58, Alexandre Belloni wrote:
>>> On 15/07/2017 at 10:20:27 -0700, Florian Fainelli wrote:
>>>>> We already have
>>>>>
>>>>> struct regulator_state {
>>>>>        int uV; /* suspend voltage */
>>>>>        unsigned int mode; /* suspend regulator operating mode */
>>>>>        int enabled; /* is regulator enabled in this suspend state */
>>>>>        int disabled; /* is the regulator disabled in this suspend state */
>>>>> };
>>>>>
>>>>>  * struct regulation_constraints - regulator operating constraints.
>>>>>   * @state_disk: State for regulator when system is suspended in disk
>>>>>   * mode.
>>>>>   * @state_mem: State for regulator when system is suspended in mem
>>>>>   * mode.
>>>>>   * @state_standby: State for regulator when system is suspended in
>>>>>   * standby
>>>>>   *                 mode.
>>>>>    
>>>>> . So it seems that maybe we should tell the drivers if we are entering
>>>>> "state_mem" or "state_standby" (something I may have opposed, sorry),
>>>>> then the driver can get neccessary information from regulator
>>>>> framework.
>>>>
>>>> OK, so what would be the mechanism to tell these drivers about the
>>>> system wide suspend state they are entering if it is not via
>>>> platform_suspend_target_state()?
>>>>
>>>> Keep in mind that regulators might be one aspect of what could be
>>>> causing the platform to behave specifically in one suspend state vs.
>>>> another, but there could be pieces of HW within the SoC that can't be
>>>> described with power domains, voltage islands etc. that would still have
>>>> inherent suspend states properties (like memory retention, pin/pad
>>>> controls etc. etc). We still need some mechanism, possibly centralized
>>>>
>>>
>>> I concur, the regulator stuff is one aspect of one of our suspend state
>>> (cutting VDDcore). But we have another state where the main clock (going
>>> to the IPs) is going from a few hundred MHz to 32kHz. This is currently
>>> handled by calling at91_suspend_entering_slow_clock(). I think it is
>>> important to take that into account so we can remove this hack from the
>>> kernel.
>>
>> Cure should not be worse then the disease... and it is in this case.
>>
>> For clocks, take a look at clock framework, perhaps it already has "clock_will_be_suspended"
>> as regulator framework had. If not, implement it.
>>
> 
> See Rafael's comment, currently, the clock framework can't say whether
> the clock will change because it doesn't know anything about the suspend
> target.
> 
>> Same with memory retention, pin/pad controls.
>>
> 
> Same here.

Exactly, here is another side effect of not knowing the platform
suspend/state that I came across on our platforms:

https://patchwork.kernel.org/patch/9561575/

(we later discussed this in details with Linus and this is why this very
patch set is being introduced now)
-- 
Florian