linux-kernel - Re: [PATCH] soc: mediatek: PMIC wrap: Enable STAUPD_PRD before WDT_SRC

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Message-ID: <1452070364.31834.60.camel@mtksdaap41>
Date:	Wed, 6 Jan 2016 16:52:44 +0800
From:	Henry Chen <henryc.chen@...iatek.com>
To:	Daniel Kurtz <djkurtz@...omium.org>
CC:	Matthias Brugger <matthias.bgg@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"moderated list:ARM/Mediatek SoC support" 
	<linux-mediatek@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] soc: mediatek: PMIC wrap: Enable STAUPD_PRD before
 WDT_SRC_EN enabled.

On Wed, 2016-01-06 at 10:37 +0800, Daniel Kurtz wrote:
> On Mon, Jan 4, 2016 at 11:05 AM, Henry Chen <henryc.chen@...iatek.com> wrote:
> > On Thu, 2015-12-31 at 22:19 +0800, Daniel Kurtz wrote:
> >> On Wed, Dec 30, 2015 at 8:36 PM, Henry Chen <henryc.chen@...iatek.com> wrote:
> >> >
> >> > The STAUPD_TRIG will be enable when WDT_INT enable on probe function, if
> >> > doesn't enable STAUPD_PRD together, interrupt will be triggered because
> >> > STAUPD timeout. To avoid unexpected interrupt, enable periodic status
> >> > update which will be updated to PMIC every selected time period.
> >>
> >> Sorry, I don't really understand this.
> >>
> >> What exactly is triggering the unexpected watchdog interrupt (WDT_INT)?
> >>
> >> How does setting STAUPD_PRD disable this "unexpected interrupt"?
> >>
> > Yes, WDT_INT was triggered because the bit[25] of WDT_SRC_EN was
> > enabled:
> >
> > bit[25] STAUPD_TRIG: STAUPD trigger signal timeout monitor
> >
> > Setting STAUPD_PRD will update the status of PMIC periodic to avoid this
> > watchdog timeout.
> 
> Sorry, I still don't understand.
Sorry, I will try to explain the behavior more clearly.
> 
> IIUC, setting STAUPD_PRD sets the period at which status updates are
> reported (announced via the shared STAUPD/WDT interrupt).
> 
> So, setting STAUPD_PRD=5 should set the reporting period to 98.5 us.
> But, how does changing this period fix the "unexpected interrupt"?

Setting STAUPD_PRD which means pmic wrap will get the status from PMIC
every 98.5us. Each time watchdog saw the STAUPD update, the interrupt
won't be trigger.

> I can understand how it might change the timing of the interrupt, but
> why does it make the interrupt no longer occur?

STAUPD_PRD was not the timer to trigger interrupt, I think what you said
was WDT_UNIT.

> We are still triggering the interrupt when we write bit[25]
> (STAUPD_TRIG) of WDT_SRC_EN, two lines later.

if STAUPD_TRIG was set, STAUPD_PRD=5 => STAUPD will trigger signal to
get the status from PMIC every 98.5us => the interrupt will not trigger,
because STAUPD_PRD working.
 
if STAUPD_TRIG was set, STAUPD_PRD=0 => STAUPD disable.=> the interrupt
will trigger by watchdog because STAUPD won't trigger the signal.

> Isn't this still requesting a STAUPD interrupt 98.5 us later?  (which,
> since STAUPD interrupts aren't handled, is an "unexpected interrupt")
> Wouldn't a better fix be to just clear the STAUPD_TRIG bit of
> WDT_SRC_EN, and just not trigger STAUPD in the first place if we can't
> handle them?
Yes. Maybe to clear the STAUPD_TRIG bit of WDT_SRC_EN was better to fix
the problem.

Henry
> 
> -Dan
> 
> >> From the MT8173 Datasheet, I can see that the value written to
> >> STAUPD_PRD is the "periodic status update timing (period)".
> >>
> >> > Signed-off-by: Henry Chen <henryc.chen@...iatek.com>
> >> > ---
> >> >  drivers/soc/mediatek/mtk-pmic-wrap.c | 5 +++++
> >> >  1 file changed, 5 insertions(+)
> >> >
> >> > diff --git a/drivers/soc/mediatek/mtk-pmic-wrap.c b/drivers/soc/mediatek/mtk-pmic-wrap.c
> >> > index a8cde17..6e5c20f 100644
> >> > --- a/drivers/soc/mediatek/mtk-pmic-wrap.c
> >> > +++ b/drivers/soc/mediatek/mtk-pmic-wrap.c
> >> > @@ -904,6 +904,11 @@ static int pwrap_probe(struct platform_device *pdev)
> >> >                 return -ENODEV;
> >> >         }
> >> >
> >> > +       /*
> >> > +        * Enable periodic status update which will be updated to PMIC
> >> > +        * every selected time period.
> >> > +        */
> >> > +       pwrap_writel(wrp, 0x5, PWRAP_STAUPD_PRD);
> >>
> >> nit: Perhaps use a define for 5, and specify the real period value.
> >> Something like this:
> >>
> >> #define PWRAP_STAUPD_98_5US  5
> >>
> > ok.
> >
> >>
> >> >         /* Initialize watchdog, may not be done by the bootloader */
> >> >         pwrap_writel(wrp, 0xf, PWRAP_WDT_UNIT);
> >> >         pwrap_writel(wrp, 0xffffffff, PWRAP_WDT_SRC_EN);
> >> > --
> >> > 1.9.1
> >> >
> >> > --
> >> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> >> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >> > Please read the FAQ at  http://www.tux.org/lkml/
> >
> >


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