linux-kernel - Re: [PATCH v2 2/3] ARM: at91: pm: add per soc validation of pm modes

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Message-ID: <20200804155636.GC10725@piout.net>
Date:   Tue, 4 Aug 2020 17:56:36 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Claudiu.Beznea@...rochip.com
Cc:     Nicolas.Ferre@...rochip.com, Ludovic.Desroches@...rochip.com,
        wenyou.yang@...el.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] ARM: at91: pm: add per soc validation of pm modes

On 04/08/2020 15:45:40+0000, Claudiu.Beznea@...rochip.com wrote:
> 
> 
> On 04.08.2020 18:08, Alexandre Belloni wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > On 04/08/2020 15:00:38+0000, Claudiu.Beznea@...rochip.com wrote:
> >>
> >>
> >> On 04.08.2020 14:42, Alexandre Belloni wrote:
> >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >>>
> >>> Hello,
> >>>
> >>> On 04/08/2020 14:07:37+0300, Claudiu Beznea wrote:
> >>>>  void __init at91rm9200_pm_init(void)
> >>>>  {
> >>>> +     static const int modes[] __initconst = {
> >>>
> >>> You don't need that to be static as it is now local to the function.
> >>>
> >>>> +             AT91_PM_STANDBY, AT91_PM_ULP0
> >>>> +     };
> >>>> +
> >>>>       if (!IS_ENABLED(CONFIG_SOC_AT91RM9200))
> >>>>               return;
> >>>>
> >>>> +     at91_pm_modes_validate(modes, ARRAY_SIZE(modes));
> >>>
> >>> For rm9200 and at91sam9, I would not allow changing the pm_modes and
> >>> simply enforce standby_mode = AT91_PM_STANDBY and suspend_mode =
> >>> AT91_PM_ULP0.I don't think you have any user that ever changed that
> >>> behaviour also that avoids increasing the boot time for those slow SoCs.
> >>
> >> OK, but bootargs is parsed at a moment when there is no information about
> >> the machine that is running the code. And enforcing this in *_pm_init()
> >> functions for rm9200 and at91sam9 may change suspend and standby mode that
> >> user selected. If there is no user up to this moment there is still the
> >> possibility of being one in the future.
> >>
> > 
> > So let's prevent users from doing that. Unused arguments are silently
> > ignored which is exactly what we want to do.
> 
> Can you share what are you thinking about? You want to not parse
> atmel.pm_modes for this machines?
> 

Well, as you said, when parsing we don't know on which machine we are
running so let's keep parsing it anyway.

> > You won't make me believe
> > there is actually a use case for swapping the standby and suspend
> > meanings.
> What i want to say is this:
> bootargs contains atmel.pm_modes=ulp0,standby
> 
> this leads to
> standby_mode=ulp0
> suspend_mode=standby
> 
> But you want in code to force
> standby_mode=standby
> suspend_mode=ulp0
> 
> The question is: is this what you are thinking this should be done?
> 

Yes, I think we need to enforce standby_mode=standby and
suspend_mode=ulp0 for rm9200 and at91sam9. This is how it always have
been.

You have two ways of doing that:

Etiher you enforce the values after parsing, in at91rm9200_pm_init and
at91sam9_pm_init. Or, when parsing your store the values in a different
location than soc_pm.data and update soc_pm.data only in sama5_pm_init,
sama5d2_pm_init and sam9x60_pm_init. I feel like the first solution is
easier.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com