linux-kernel - Re: [PATCH v2 3/3] watchdog: sama5d4: Implement resume hook

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Date:   Fri, 17 Feb 2017 16:22:01 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Wim Van Sebroeck <wim@...ana.be>,
        Nicolas Ferre <nicolas.ferre@...el.com>,
        linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] watchdog: sama5d4: Implement resume hook

On 17/02/2017 at 06:47:03 -0800, Guenter Roeck wrote:
> On 02/16/2017 11:30 AM, Alexandre Belloni wrote:
> > When resuming for the deepest state on sama5d2, it is necessary to restore
> > MR as the registers are lost.
> > 
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> > ---
> > Changes in v2:
> >  - cache mr beofre suspending
> > 
> >  drivers/watchdog/sama5d4_wdt.c | 32 ++++++++++++++++++++++++++++++++
> >  1 file changed, 32 insertions(+)
> > 
> > diff --git a/drivers/watchdog/sama5d4_wdt.c b/drivers/watchdog/sama5d4_wdt.c
> > index 2a60251806d2..5ddeb4803dc3 100644
> > --- a/drivers/watchdog/sama5d4_wdt.c
> > +++ b/drivers/watchdog/sama5d4_wdt.c
> > @@ -28,6 +28,7 @@
> >  struct sama5d4_wdt {
> >  	struct watchdog_device	wdd;
> >  	void __iomem		*reg_base;
> > +	u32			mr;
> 
> Makes me wonder if we shouldn't just retain the original 'config'
> (and maybe rename it to 'mr). After all, it _is_ used now.
> 
> >  };
> > 
> >  static int wdt_timeout = WDT_DEFAULT_TIMEOUT;
> > @@ -248,11 +249,42 @@ static const struct of_device_id sama5d4_wdt_of_match[] = {
> >  };
> >  MODULE_DEVICE_TABLE(of, sama5d4_wdt_of_match);
> > 
> > +#ifdef CONFIG_PM_SLEEP
> > +static int sama5d4_wdt_suspend(struct device *dev)
> > +{
> > +	struct sama5d4_wdt *wdt = dev_get_drvdata(dev);
> > +
> > +	wdt->mr = wdt_read(wdt, AT91_WDT_MR);
> > +
> 
> Wouldn't you want to stop the watchdog here if it is running,
> ie set AT91_WDT_WDDIS ?
> 

Some existing customers want the watchdog to continue to run while the
system is suspended.

> > +	return 0;
> > +}
> > +
> > +static int sama5d4_wdt_resume(struct device *dev)
> > +{
> > +	struct sama5d4_wdt *wdt = dev_get_drvdata(dev);
> > +	u32 reg;
> > +
> > +	reg = wdt_read(wdt, AT91_WDT_MR);
> > +	if (reg & AT91_WDT_WDDIS)
> > +		wdt_write(wdt, AT91_WDT_MR, reg & ~AT91_WDT_WDDIS);
> > +
> > +	wdt_write(wdt, AT91_WDT_MR, wdt->mr & ~AT91_WDT_WDDIS);
> 
> Is that necessary ? Why not just write wdt->mr unconditionally ?
> 

Because you can change WDV and WDD *OR* WDDIS but not both at the same
time.

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