linux-kernel - RE: [PATCH 07/12] pm: at91: the standby mode uses the same sram function as the suspend to memory mode

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Message-ID: <B256D81BAE5131468A838E5D7A243641BFD3484F@penmbx01>
Date:	Mon, 26 Jan 2015 03:08:46 +0000
From:	"Yang, Wenyou" <Wenyou.Yang@...el.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Sylvain Rochet <sylvain.rochet@...secur.com>
CC:	"Ferre, Nicolas" <Nicolas.FERRE@...el.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"peda@...ntia.se" <peda@...ntia.se>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH 07/12] pm: at91: the standby mode uses the same sram
 function as the suspend to memory mode

Hi Alexandre,

Thank you for review.

> -----Original Message-----
> From: Alexandre Belloni [mailto:alexandre.belloni@...e-electrons.com]
> Sent: Saturday, January 24, 2015 7:02 AM
> To: Sylvain Rochet
> Cc: Yang, Wenyou; Ferre, Nicolas; linux@....linux.org.uk; linux-
> kernel@...r.kernel.org; peda@...ntia.se; linux-arm-kernel@...ts.infradead.org
> Subject: Re: [PATCH 07/12] pm: at91: the standby mode uses the same sram
> function as the suspend to memory mode
> 
> On 23/01/2015 at 18:32:34 +0100, Sylvain Rochet wrote :
> > Hello Wenyou,
> >
> > On Tue, Jan 20, 2015 at 04:17:00PM +0800, Wenyou Yang wrote:
> > >
> > > diff --git a/arch/arm/mach-at91/pm.c b/arch/arm/mach-at91/pm.c index
> > > 691e6db..a1010f0 100644
> > > --- a/arch/arm/mach-at91/pm.c
> > > +++ b/arch/arm/mach-at91/pm.c
> >   (...)
> > >  static int at91_pm_enter(suspend_state_t state)  {
> > >  	at91_pinctrl_gpio_suspend();
> > >
> > >  	switch (state) {
> > > +	/*
> > > +	 * Suspend-to-RAM is like STANDBY plus slow clock mode, so
> > > +	 * drivers must suspend more deeply, the master clock switches
> > > +	 * to the clk32k and turns off the main oscillator
> > > +	 *
> > > +	 * STANDBY mode has *all* drivers suspended; ignores irqs not
> > > +	 * marked as 'wakeup' event sources; and reduces DRAM power.
> > > +	 * But otherwise it's identical to PM_SUSPEND_ON:  cpu idle, and
> > > +	 * nothing fancy done with main or cpu clocks.
> > > +	 */
> > > +	case PM_SUSPEND_MEM:
> > > +	case PM_SUSPEND_STANDBY:
> >    (...)
> > > -		case PM_SUSPEND_MEM:
> > > -			/*
> > > -			 * Ensure that clocks are in a valid state.
> > > -			 */
> > > -			if (!at91_pm_verify_clocks())
> > > -				goto error;
> >    (...)
> > > +		if (!at91_pm_verify_clocks())
> > > +			goto error;
> > >
> >    (...)
> > > -		case PM_SUSPEND_STANDBY:
> > > -			/*
> > > -			 * NOTE: the Wait-for-Interrupt instruction needs to be
> >
> > By doing that at91_pm_verify_clocks() is now called for both MEM and
> > STANDBY targets.
> >
> > In my opinion this function is misnamed and should be called
> > at91_pm_verify_clocks_for_slow_clock_mode(). This function actually
> > checks if we can safely switch to slow clock mode, if some peripherals
> > are still using the master clock, we abort the suspend because we
> > can't suspend in good condition. Hard unclocking peripherals which ask
> > for a soft stop, like USB controllers, is something we should avoid doing.
> >
> > This function checks if USB PLL and PLL B are stopped, if PCK0..PCK3
> > are stopped too (or just using the 32k clock). If all drivers
> > suspended correctly this is the state we expect and we can suspend in
> > a deep state.
> >
> > Not this is currently not the case in linux-next, suspend/resume
> > support to all Atmel USB drivers
> > (ehci-atmel,ohci-at91,atmel_usba,at91_udc) are in my series:
> >  [PATCHv7 0/6] USB: host: Atmel OHCI and EHCI drivers improvements
> >    <1421761144-11767-1-git-send-email-sylvain.rochet@...secur.com>
> >  [PATCHv6 0/5] USB: gadget: atmel_usba_udc: Driver improvements
> >    <1421945805-31129-1-git-send-email-sylvain.rochet@...secur.com>
> >
> > We are not going to change any clock for STANDBY target, there is no
> > clock to check, so we don't need to call at91_pm_verify_clocks() for
> > this target.
> >
> 
> I think we should actually stop checking those clocks. In the meantime, you are
> right and at91_pm_verify_clocks must not be called unconditionally.

Thanks.

I will change, the at91_pm_verify_clocks is only called for suspend to memory mode, not for the standby.

> 
> --
> Alexandre Belloni, Free Electrons
> Embedded Linux, Kernel and Android engineering http://free-electrons.com

Best Regards,
Wenyou Yang
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