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Date:   Thu, 30 Jul 2020 09:52:40 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Anson Huang <Anson.Huang@nxp.com>
Cc:     wim@linux-watchdog.org, shawnguo@kernel.org,
        s.hauer@pengutronix.de, kernel@pengutronix.de, festevam@gmail.com,
        linux-watchdog@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Linux-imx@nxp.com
Subject: Re: [PATCH V3 1/2] watchdog: imx7ulp: Strictly follow the sequence
 for wdog operations
Message-ID: <20200730165240.GA178323@roeck-us.net>
References: <1596074591-4207-1-git-send-email-Anson.Huang@nxp.com>
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On Thu, Jul 30, 2020 at 10:03:10AM +0800, Anson Huang wrote:
> According to reference manual, the i.MX7ULP WDOG's operations except
> refresh should follow below sequence:
> 
> 1. disable global interrupts;
> 2. unlock the wdog and wait unlock bit set;
> 3. reconfigure the wdog and wait for reconfiguration bit set;
> 4. enabel global interrupts.
> 
> Strictly follow the recommended sequence can make it more robust.
> 
> Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
> ---
> changes since V2:
> 	- change the wait timeout to 20us according to experiment;
> 	- drop WARN_ON when timeout, and check its return value in each caller for
> 	  unlock wait, no need to handle the return value for reconfiguration.
> ---
>  drivers/watchdog/imx7ulp_wdt.c | 74 ++++++++++++++++++++++++++++++++++--------
>  1 file changed, 61 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/watchdog/imx7ulp_wdt.c b/drivers/watchdog/imx7ulp_wdt.c
> index 7993c8c..010ddd1 100644
> --- a/drivers/watchdog/imx7ulp_wdt.c
> +++ b/drivers/watchdog/imx7ulp_wdt.c
> @@ -5,6 +5,7 @@
>  
>  #include <linux/clk.h>
>  #include <linux/io.h>
> +#include <linux/iopoll.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> @@ -36,6 +37,7 @@
>  #define DEFAULT_TIMEOUT	60
>  #define MAX_TIMEOUT	128
>  #define WDOG_CLOCK_RATE	1000
> +#define WDOG_WAIT_TIMEOUT	20
>  
>  static bool nowayout = WATCHDOG_NOWAYOUT;
>  module_param(nowayout, bool, 0000);
> @@ -48,17 +50,40 @@ struct imx7ulp_wdt_device {
>  	struct clk *clk;
>  };
>  
> -static void imx7ulp_wdt_enable(struct watchdog_device *wdog, bool enable)
> +static int imx7ulp_wdt_wait(void __iomem *base, u32 mask)
> +{
> +	u32 val = readl(base + WDOG_CS);
> +
> +	if (!(val & mask) && readl_poll_timeout_atomic(base + WDOG_CS, val,
> +						       val & mask, 0,
> +						       WDOG_WAIT_TIMEOUT))
> +		return -ETIMEDOUT;
> +
> +	return 0;
> +}
> +
> +static int imx7ulp_wdt_enable(struct watchdog_device *wdog, bool enable)
>  {
>  	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
>  
>  	u32 val = readl(wdt->base + WDOG_CS);
> +	int ret;
>  
> +	local_irq_disable();
>  	writel(UNLOCK, wdt->base + WDOG_CNT);
> +	ret = imx7ulp_wdt_wait(wdt->base, WDOG_CS_ULK);
> +	if (ret)
> +		goto enable_out;
>  	if (enable)
>  		writel(val | WDOG_CS_EN, wdt->base + WDOG_CS);
>  	else
>  		writel(val & ~WDOG_CS_EN, wdt->base + WDOG_CS);
> +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_RCS);
> +
> +enable_out:
> +	local_irq_enable();
> +
> +	return ret;
>  }
>  
>  static bool imx7ulp_wdt_is_enabled(void __iomem *base)
> @@ -79,17 +104,12 @@ static int imx7ulp_wdt_ping(struct watchdog_device *wdog)
>  
>  static int imx7ulp_wdt_start(struct watchdog_device *wdog)
>  {
> -
> -	imx7ulp_wdt_enable(wdog, true);
> -
> -	return 0;
> +	return imx7ulp_wdt_enable(wdog, true);
>  }
>  
>  static int imx7ulp_wdt_stop(struct watchdog_device *wdog)
>  {
> -	imx7ulp_wdt_enable(wdog, false);
> -
> -	return 0;
> +	return imx7ulp_wdt_enable(wdog, false);
>  }
>  
>  static int imx7ulp_wdt_set_timeout(struct watchdog_device *wdog,
> @@ -97,22 +117,37 @@ static int imx7ulp_wdt_set_timeout(struct watchdog_device *wdog,
>  {
>  	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
>  	u32 val = WDOG_CLOCK_RATE * timeout;
> +	int ret;
>  
> +	local_irq_disable();
>  	writel(UNLOCK, wdt->base + WDOG_CNT);
> +	ret = imx7ulp_wdt_wait(wdt->base, WDOG_CS_ULK);
> +	if (ret)
> +		goto timeout_out;
>  	writel(val, wdt->base + WDOG_TOVAL);
> +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_RCS);
> +
> +timeout_out:
> +	local_irq_enable();
>  
>  	wdog->timeout = timeout;

This needs to be moved up - the timeout did not get changed on error.

Guenter

>  
> -	return 0;
> +	return ret;
>  }
>  
>  static int imx7ulp_wdt_restart(struct watchdog_device *wdog,
>  			       unsigned long action, void *data)
>  {
>  	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
> +	int ret;
> +
> +	ret = imx7ulp_wdt_enable(wdog, true);
> +	if (ret)
> +		return ret;
>  
> -	imx7ulp_wdt_enable(wdog, true);
> -	imx7ulp_wdt_set_timeout(&wdt->wdd, 1);
> +	ret = imx7ulp_wdt_set_timeout(&wdt->wdd, 1);
> +	if (ret)
> +		return ret;
>  
>  	/* wait for wdog to fire */
>  	while (true)
> @@ -136,19 +171,30 @@ static const struct watchdog_info imx7ulp_wdt_info = {
>  		    WDIOF_MAGICCLOSE,
>  };
>  
> -static void imx7ulp_wdt_init(void __iomem *base, unsigned int timeout)
> +static int imx7ulp_wdt_init(void __iomem *base, unsigned int timeout)
>  {
>  	u32 val;
> +	int ret;
>  
> +	local_irq_disable();
>  	/* unlock the wdog for reconfiguration */
>  	writel_relaxed(UNLOCK_SEQ0, base + WDOG_CNT);
>  	writel_relaxed(UNLOCK_SEQ1, base + WDOG_CNT);
> +	ret = imx7ulp_wdt_wait(base, WDOG_CS_ULK);
> +	if (ret)
> +		goto init_out;
>  
>  	/* set an initial timeout value in TOVAL */
>  	writel(timeout, base + WDOG_TOVAL);
>  	/* enable 32bit command sequence and reconfigure */
>  	val = WDOG_CS_CMD32EN | WDOG_CS_CLK | WDOG_CS_UPDATE;
>  	writel(val, base + WDOG_CS);
> +	imx7ulp_wdt_wait(base, WDOG_CS_RCS);
> +
> +init_out:
> +	local_irq_enable();
> +
> +	return ret;
>  }
>  
>  static void imx7ulp_wdt_action(void *data)
> @@ -199,7 +245,9 @@ static int imx7ulp_wdt_probe(struct platform_device *pdev)
>  	watchdog_stop_on_reboot(wdog);
>  	watchdog_stop_on_unregister(wdog);
>  	watchdog_set_drvdata(wdog, imx7ulp_wdt);
> -	imx7ulp_wdt_init(imx7ulp_wdt->base, wdog->timeout * WDOG_CLOCK_RATE);
> +	ret = imx7ulp_wdt_init(imx7ulp_wdt->base, wdog->timeout * WDOG_CLOCK_RATE);
> +	if (ret)
> +		return ret;
>  
>  	return devm_watchdog_register_device(dev, wdog);
>  }
> -- 
> 2.7.4
>