linux-kernel - Re: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the sequence for wdog operations

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Message-ID: <00587a78-8069-4fbd-7e02-b774d541f75a@roeck-us.net>
Date:   Tue, 28 Jul 2020 21:15:02 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Anson Huang <Anson.Huang@....com>, wim@...ux-watchdog.org,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Linux-imx@....com
Subject: Re: [PATCH V2 1/2] watchdog: imx7ulp: Strictly follow the sequence
 for wdog operations

On 7/28/20 7:20 PM, Anson Huang wrote:
> According to reference manual, the i.MX7ULP WDOG's operations 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@....com>
> ---
> Changes since V1:
> 	- use readl_poll_timeout_atomic() instead of usleep_ranges() since IRQ is disabled.
> ---
>  drivers/watchdog/imx7ulp_wdt.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/watchdog/imx7ulp_wdt.c b/drivers/watchdog/imx7ulp_wdt.c
> index 7993c8c..7d2b12e 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	10000
>  
>  static bool nowayout = WATCHDOG_NOWAYOUT;
>  module_param(nowayout, bool, 0000);
> @@ -48,17 +50,31 @@ struct imx7ulp_wdt_device {
>  	struct clk *clk;
>  };
>  
> +static inline void imx7ulp_wdt_wait(void __iomem *base, u32 mask)
> +{
> +	u32 val = readl(base + WDOG_CS);
> +
> +	if (!(val & mask))
> +		WARN_ON(readl_poll_timeout_atomic(base + WDOG_CS, val,
> +						  val & mask, 0,
> +						  WDOG_WAIT_TIMEOUT));

I am not a friend of WARN_ON, especially in situations like this.
Please explain why this is needed, and why a return of -ETIMEDOUT
is not feasible.

Also, I do not believe that a 10 milli-second timeout is warranted.
This will need to be backed up by the datasheet.

Guenter

> +}
> +
>  static void 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);
>  
> +	local_irq_disable();
>  	writel(UNLOCK, wdt->base + WDOG_CNT);
> +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_ULK);
>  	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);
> +	local_irq_enable();
>  }
>  
>  static bool imx7ulp_wdt_is_enabled(void __iomem *base)
> @@ -72,7 +88,12 @@ static int imx7ulp_wdt_ping(struct watchdog_device *wdog)
>  {
>  	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
>  
> +	local_irq_disable();
> +	writel(UNLOCK, wdt->base + WDOG_CNT);
> +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_ULK);
>  	writel(REFRESH, wdt->base + WDOG_CNT);
> +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_RCS);
> +	local_irq_enable();
>  
>  	return 0;
>  }
> @@ -98,8 +119,12 @@ 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;
>  
> +	local_irq_disable();
>  	writel(UNLOCK, wdt->base + WDOG_CNT);
> +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_ULK);
>  	writel(val, wdt->base + WDOG_TOVAL);
> +	imx7ulp_wdt_wait(wdt->base, WDOG_CS_RCS);
> +	local_irq_enable();
>  
>  	wdog->timeout = timeout;
>  
> @@ -140,15 +165,19 @@ static void imx7ulp_wdt_init(void __iomem *base, unsigned int timeout)
>  {
>  	u32 val;
>  
> +	local_irq_disable();
>  	/* unlock the wdog for reconfiguration */
>  	writel_relaxed(UNLOCK_SEQ0, base + WDOG_CNT);
>  	writel_relaxed(UNLOCK_SEQ1, base + WDOG_CNT);
> +	imx7ulp_wdt_wait(base, WDOG_CS_ULK);
>  
>  	/* 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);
> +	local_irq_enable();
>  }
>  
>  static void imx7ulp_wdt_action(void *data)
>