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Message-ID: <20190426141651.GA1715@roeck-us.net>
Date: Fri, 26 Apr 2019 07:16:51 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Ludovic Barre <ludovic.Barre@...com>
Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>,
Rob Herring <robh+dt@...nel.org>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...com>,
linux-watchdog@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org,
linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH] watchdog: stm32: add dynamic prescaler support
On Fri, Apr 26, 2019 at 03:41:15PM +0200, Ludovic Barre wrote:
> From: Ludovic Barre <ludovic.barre@...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@...com>
> ---
> drivers/watchdog/stm32_iwdg.c | 70 +++++++++++++++++++++++++------------------
> 1 file changed, 41 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/watchdog/stm32_iwdg.c b/drivers/watchdog/stm32_iwdg.c
> index e00e3b3..91d0a89 100644
> --- a/drivers/watchdog/stm32_iwdg.c
> +++ b/drivers/watchdog/stm32_iwdg.c
> @@ -34,18 +34,10 @@
> #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
>
> /* 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_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 +47,28 @@
> #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)
> @@ -80,21 +85,30 @@ 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 timeout, presc, iwdg_rlr, iwdg_pr;
> int ret;
>
> 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);
> + timeout = clamp_t(unsigned int, wdd->timeout,
> + wdd->min_timeout, wdd->max_hw_heartbeat_ms / 1000);
> +
> + if (timeout != wdd->timeout)
> + dev_warn(wdd->parent, "timeout skrinked to %d\n", timeout);
> +
Valid values for timeout should be set in the set_timeout function,
not here. As such, there is no need for this warning. More specifically,
if the selected timeout is between min_timeout and max_hw_heartbeat_ms,
and the hardware can not meet the exact requested value, the set_timeout
function should adjust wdd->timeout value accordingly.
Example: The requested timeout is 55 seconds, but the hardware can
only support either 32 or 64 seconds. The set_timeout function should
then set wdd->timeout to either 32 or 64.
Furthermore, this is a valid condition. For example, the timeout could
be set for one hour (or day), and the maximum heartbeat could be one
minute. In that situation, the watchdog core handles heartbeat/ping
requests. Again, this does not warrant a warning.
On top of all that, if the hardware can not set a minimum timeout of
1 second, min_timeout should not be set to 1 second. It should be set
to the actual minimum supportable value if that value is larger than
1 second.
> + presc = DIV_ROUND_UP(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 = ((timeout * wdt->rate) / presc) - 1;
>
> /* 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_PR, iwdg_pr);
> + reg_write(wdt->regs, IWDG_RLR, iwdg_rlr);
> reg_write(wdt->regs, IWDG_KR, KR_KEY_ENABLE);
>
> /* wait for the registers to be updated (max 100ms) */
> @@ -150,7 +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");
> @@ -191,8 +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);
> @@ -200,20 +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);
> @@ -231,8 +242,9 @@ 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 = 1;
Is this guaranteed to be no larger than 1 under all circumstances ?
[ Not that the old code was necessarily correct - it might have set
min_timeout to 0 if wdt->rate is high ]
> + 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
>
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