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Date:   Thu, 2 May 2019 13:35:25 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Ludovic Barre <ludovic.Barre@st.com>
Cc:     Wim Van Sebroeck <wim@linux-watchdog.org>,
        Rob Herring <robh+dt@kernel.org>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        linux-watchdog@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org,
        linux-stm32@st-md-mailman.stormreply.com
Subject: Re: [PATCH V2 3/3] watchdog: stm32: add dynamic prescaler support
Message-ID: <20190502203525.GA29063@roeck-us.net>
References: <1556806126-15890-1-git-send-email-ludovic.Barre@st.com>
 <1556806126-15890-4-git-send-email-ludovic.Barre@st.com>
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On Thu, May 02, 2019 at 04:08:46PM +0200, Ludovic Barre wrote:
> From: Ludovic Barre <ludovic.barre@st.com>
> 
> This patch allows to define the max prescaler by compatible.
> To set a large range of timeout, the prescaler should be set
> dynamically (from the timeout request) to improve the resolution
> in order to have a timeout close to the expected value.
> 
> Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
> ---
>  drivers/watchdog/stm32_iwdg.c | 76 ++++++++++++++++++++++++-------------------
>  1 file changed, 42 insertions(+), 34 deletions(-)
> 
> diff --git a/drivers/watchdog/stm32_iwdg.c b/drivers/watchdog/stm32_iwdg.c
> index f19a6d4..0c765d4 100644
> --- a/drivers/watchdog/stm32_iwdg.c
> +++ b/drivers/watchdog/stm32_iwdg.c
> @@ -34,18 +34,12 @@
>  #define KR_KEY_EWA	0x5555 /* write access enable */
>  #define KR_KEY_DWA	0x0000 /* write access disable */
>  
> -/* IWDG_PR register bit values */
> -#define PR_4		0x00 /* prescaler set to 4 */
> -#define PR_8		0x01 /* prescaler set to 8 */
> -#define PR_16		0x02 /* prescaler set to 16 */
> -#define PR_32		0x03 /* prescaler set to 32 */
> -#define PR_64		0x04 /* prescaler set to 64 */
> -#define PR_128		0x05 /* prescaler set to 128 */
> -#define PR_256		0x06 /* prescaler set to 256 */
> +#define PR_SHIFT	2
> +#define PR_MIN		BIT(PR_SHIFT)
>  
>  /* IWDG_RLR register values */
> -#define RLR_MIN		0x07C /* min value supported by reload register */
> -#define RLR_MAX		0xFFF /* max value supported by reload register */
> +#define RLR_MIN		0x2		/* min value recommended */
> +#define RLR_MAX		GENMASK(11, 0)	/* max value of reload register */
>  
>  /* IWDG_SR register bit mask */
>  #define FLAG_PVU	BIT(0) /* Watchdog prescaler value update */
> @@ -55,15 +49,28 @@
>  #define TIMEOUT_US	100000
>  #define SLEEP_US	1000
>  
> -#define HAS_PCLK	true
> +struct stm32_iwdg_data {
> +	bool has_pclk;
> +	u32 max_prescaler;
> +};
> +
> +static const struct stm32_iwdg_data stm32_iwdg_data = {
> +	.has_pclk = false,
> +	.max_prescaler = 256,
> +};
> +
> +static const struct stm32_iwdg_data stm32mp1_iwdg_data = {
> +	.has_pclk = true,
> +	.max_prescaler = 1024,
> +};
>  
>  struct stm32_iwdg {
>  	struct watchdog_device	wdd;
> +	const struct stm32_iwdg_data *data;
>  	void __iomem		*regs;
>  	struct clk		*clk_lsi;
>  	struct clk		*clk_pclk;
>  	unsigned int		rate;
> -	bool			has_pclk;
>  };
>  
>  static inline u32 reg_read(void __iomem *base, u32 reg)
> @@ -79,26 +86,28 @@ static inline void reg_write(void __iomem *base, u32 reg, u32 val)
>  static int stm32_iwdg_start(struct watchdog_device *wdd)
>  {
>  	struct stm32_iwdg *wdt = watchdog_get_drvdata(wdd);
> -	u32 val = FLAG_PVU | FLAG_RVU;
> -	u32 reload;
> +	u32 presc, iwdg_rlr, iwdg_pr, iwdg_sr;
>  
>  	dev_dbg(wdd->parent, "%s\n", __func__);
>  
> -	/* prescaler fixed to 256 */
> -	reload = clamp_t(unsigned int, ((wdd->timeout * wdt->rate) / 256) - 1,
> -			 RLR_MIN, RLR_MAX);
> +	presc = DIV_ROUND_UP(wdd->timeout * wdt->rate, RLR_MAX + 1);
> +
> +	/* The prescaler is align on power of 2 and start at 2 ^ PR_SHIFT. */
> +	presc = roundup_pow_of_two(presc);
> +	iwdg_pr = presc <= 1 << PR_SHIFT ? 0 : ilog2(presc) - PR_SHIFT;
> +	iwdg_rlr = ((wdd->timeout * wdt->rate) / presc) - 1;
>  
> +	/* enable watchdog */
> +	reg_write(wdt->regs, IWDG_KR, KR_KEY_ENABLE);
>  	/* enable write access */
>  	reg_write(wdt->regs, IWDG_KR, KR_KEY_EWA);
> -
>  	/* set prescaler & reload registers */
> -	reg_write(wdt->regs, IWDG_PR, PR_256); /* prescaler fix to 256 */
> -	reg_write(wdt->regs, IWDG_RLR, reload);
> -	reg_write(wdt->regs, IWDG_KR, KR_KEY_ENABLE);
> +	reg_write(wdt->regs, IWDG_PR, iwdg_pr);
> +	reg_write(wdt->regs, IWDG_RLR, iwdg_rlr);
>  
>  	/* wait for the registers to be updated (max 100ms) */
> -	if (readl_relaxed_poll_timeout(wdt->regs + IWDG_SR, val,
> -				       !(val & (FLAG_PVU | FLAG_RVU)),
> +	if (readl_relaxed_poll_timeout(wdt->regs + IWDG_SR, iwdg_sr,
> +				       !(iwdg_sr & (FLAG_PVU | FLAG_RVU)),
>  				       SLEEP_US, TIMEOUT_US)) {
>  		dev_err(wdd->parent, "Fail to set prescaler, reload regs\n");
>  		return -EIO;

As mentioned in the other patch, pelase return the error returned from
readl_relaxed_poll_timeout(). If that returns a timeout, we want to know
about it and not just hide it behind -EIO.

> @@ -155,7 +164,7 @@ static int stm32_iwdg_clk_init(struct platform_device *pdev,
>  	}
>  
>  	/* optional peripheral clock */
> -	if (wdt->has_pclk) {
> +	if (wdt->data->has_pclk) {
>  		wdt->clk_pclk = devm_clk_get(&pdev->dev, "pclk");
>  		if (IS_ERR(wdt->clk_pclk)) {
>  			dev_err(&pdev->dev, "Unable to get pclk clock\n");
> @@ -196,8 +205,8 @@ static const struct watchdog_ops stm32_iwdg_ops = {
>  };
>  
>  static const struct of_device_id stm32_iwdg_of_match[] = {
> -	{ .compatible = "st,stm32-iwdg", .data = (void *)!HAS_PCLK },
> -	{ .compatible = "st,stm32mp1-iwdg", .data = (void *)HAS_PCLK },
> +	{ .compatible = "st,stm32-iwdg", .data = &stm32_iwdg_data },
> +	{ .compatible = "st,stm32mp1-iwdg", .data = &stm32mp1_iwdg_data },
>  	{ /* end node */ }
>  };
>  MODULE_DEVICE_TABLE(of, stm32_iwdg_of_match);
> @@ -205,20 +214,17 @@ MODULE_DEVICE_TABLE(of, stm32_iwdg_of_match);
>  static int stm32_iwdg_probe(struct platform_device *pdev)
>  {
>  	struct watchdog_device *wdd;
> -	const struct of_device_id *match;
>  	struct stm32_iwdg *wdt;
>  	struct resource *res;
>  	int ret;
>  
> -	match = of_match_device(stm32_iwdg_of_match, &pdev->dev);
> -	if (!match)
> -		return -ENODEV;
> -
>  	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
>  	if (!wdt)
>  		return -ENOMEM;
>  
> -	wdt->has_pclk = match->data;
> +	wdt->data = of_device_get_match_data(&pdev->dev);
> +	if (!wdt->data)
> +		return -ENODEV;
>  
>  	/* This is the timer base. */
>  	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> @@ -236,8 +242,10 @@ static int stm32_iwdg_probe(struct platform_device *pdev)
>  	wdd = &wdt->wdd;
>  	wdd->info = &stm32_iwdg_info;
>  	wdd->ops = &stm32_iwdg_ops;
> -	wdd->min_timeout = ((RLR_MIN + 1) * 256) / wdt->rate;
> -	wdd->max_hw_heartbeat_ms = ((RLR_MAX + 1) * 256 * 1000) / wdt->rate;
> +	wdd->min_timeout = max_t(unsigned int, 1,
> +				 (((RLR_MIN + 1) * PR_MIN) / wdt->rate));

Is that any different to DIV_ROUND_UP() ?

> +	wdd->max_hw_heartbeat_ms = ((RLR_MAX + 1) * wdt->data->max_prescaler *
> +				    1000) / wdt->rate;
>  	wdd->parent = &pdev->dev;
>  
>  	watchdog_set_drvdata(wdd, wdt);
> -- 
> 2.7.4
>