[v2] watchdog: imx2_wdg: Alow ping on suspend

The i.MX watchdog cannot be disabled by softwrae once it has been
enabled. This means that it can't be stopped before suspend.

For systems that enter low power mode this is fine, as the watchdog will
be automatically stopped by hardwrae in low power mode. Not all i.MX
platforms support low power mode in the mainline kernel. For example the
i.MX7D does not enter low power mode and so will be rebooted 2 minutes
after entering freeze or mem sleep states.

This patch introduces a device tree property "fsl,ping-during-suspend"
that can be used to enable ping on suspend support for these systems.

Signed-off-by: Alistair Francis <alistair@alistair23.me>
---
 drivers/watchdog/imx2_wdt.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

On Tue, 25 Jan 2022, at 2:21 AM, Guenter Roeck wrote:
> On 1/24/22 04:00, Alistair Francis wrote:
> > The i.MX watchdog cannot be disabled by softwrae once it has been
> 
> s/softwrae/software/
> 
> > enabled. This means that it can't be stopped before suspend.
> > 
> > For systems that enter low power mode this is fine, as the watchdog will
> > be automatically stopped by hardwrae in low power mode. Not all i.MX
> 
> s/hardwrae/hardware/
> 
> > platforms support low power mode in the mainline kernel. For example the
> > i.MX7D does not enter low power mode and so will be rebooted 2 minutes
> > after entering freeze or mem sleep states.
> 
> I don't think "mem" adds any value here. Just make it sleep states.
> 
> > 
> > This patch introduces a device tree property "fsl,ping-during-suspend"
> > that can be used to enable ping on suspend support for these systems.
> > 
> > Signed-off-by: Alistair Francis <alistair@alistair23.me>
> > ---
> 
> Change log goes here.
> 
> >   drivers/watchdog/imx2_wdt.c | 27 ++++++++++++++++++++-------
> >   1 file changed, 20 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> > index 51bfb796898b..d0c5d47ddede 100644
> > --- a/drivers/watchdog/imx2_wdt.c
> > +++ b/drivers/watchdog/imx2_wdt.c
> > @@ -66,6 +66,7 @@ struct imx2_wdt_device {
> >   struct watchdog_device wdog;   
> >   bool ext_reset;
> >   bool clk_is_on;
> 
> I don't see the purpose of this variable. Unless I am missing something is is set
> but never used.

clk_is_on is used in imx2_wdt_ping(), it disables the access if
the clock isn't running.

> 
> > + bool no_ping;
> >   };
> >   
> >   static bool nowayout = WATCHDOG_NOWAYOUT;
> > @@ -312,12 +313,18 @@ static int __init imx2_wdt_probe(struct platform_device *pdev)
> >   
> >   wdev->ext_reset = of_property_read_bool(dev->of_node,
> >   "fsl,ext-reset-output");
> > + /*
> > + * The i.MX7D doesn't support low power mode, so we need to ping the watchdog
> > + * during suspend.
> > + */
> > + wdev->no_ping = !of_device_is_compatible(dev->of_node, "fsl,imx7d-wdt");
> 
> This is ok as long as there is only a single chip requiring this change.
> If there are more, the 'data' field in struct of_device_id should be used
> instead.

I only know of one now, so this should be fine then.

Alistair

> 
> >   platform_set_drvdata(pdev, wdog);
> >   watchdog_set_drvdata(wdog, wdev);
> >   watchdog_set_nowayout(wdog, nowayout);
> >   watchdog_set_restart_priority(wdog, 128);
> >   watchdog_init_timeout(wdog, timeout, dev);
> > - watchdog_stop_ping_on_suspend(wdog);
> > + if (wdev->no_ping)
> > + watchdog_stop_ping_on_suspend(wdog);
> >   
> >   if (imx2_wdt_is_running(wdev)) {
> >   imx2_wdt_set_timeout(wdog, wdog->timeout);
> > @@ -366,9 +373,11 @@ static int __maybe_unused imx2_wdt_suspend(struct device *dev)
> >   imx2_wdt_ping(wdog);
> >   }
> >   
> > - clk_disable_unprepare(wdev->clk);
> > + if (wdev->no_ping) {
> > + clk_disable_unprepare(wdev->clk);
> >   
> > - wdev->clk_is_on = false;
> > + wdev->clk_is_on = false;
> > + }
> >   
> >   return 0;
> >   }
> > @@ -380,11 +389,14 @@ static int __maybe_unused imx2_wdt_resume(struct device *dev)
> >   struct imx2_wdt_device *wdev = watchdog_get_drvdata(wdog);
> >   int ret;
> >   
> > - ret = clk_prepare_enable(wdev->clk);
> > - if (ret)
> > - return ret;
> > + if (wdev->no_ping) {
> > + ret = clk_prepare_enable(wdev->clk);
> >   
> > - wdev->clk_is_on = true;
> > + if (ret)
> > + return ret;
> > +
> > + wdev->clk_is_on = true;
> > + }
> >   
> >   if (watchdog_active(wdog) && !imx2_wdt_is_running(wdev)) {
> >   /*
> > @@ -407,6 +419,7 @@ static SIMPLE_DEV_PM_OPS(imx2_wdt_pm_ops, imx2_wdt_suspend,
> >   
> >   static const struct of_device_id imx2_wdt_dt_ids[] = {
> >   { .compatible = "fsl,imx21-wdt", },
> > + { .compatible = "fsl,imx7d-wdt", },
> >   { /* sentinel */ }
> >   };
> >   MODULE_DEVICE_TABLE(of, imx2_wdt_dt_ids);
> 
>