linux-kernel - Re: [PATCH v2] watchdog: imx2

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Message-Id: <6b0d3b85-a3a3-4f06-a6c1-88fa0a4113f0@www.fastmail.com>
Date:   Thu, 27 Jan 2022 20:35:33 +1000
From:   Alistair <alistair@...stair23.me>
To:     "Guenter Roeck" <linux@...ck-us.net>,
        linux-arm-kernel@...ts.infradead.org, shawnguo@...nel.org,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        s.hauer@...gutronix.de, linux-watchdog@...r.kernel.org,
        wim@...ux-watchdog.org
Cc:     devicetree@...r.kernel.org, festevam@...il.com, linux-imx@....com,
        "Rob Herring" <robh+dt@...nel.org>, kernel@...gutronix.de
Subject: Re: [PATCH v2] watchdog: imx2_wdg: Alow ping on suspend

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@...stair23.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);
> 
>