Subject: Re: [PATCH 2/3] watchdog: sam9x60_wdt: introduce sam9x60 watchdog timer driver

From: Alexandre Belloni <[email-masked]>
Date: Wed, 2 Oct 2019 12:23:55 +0200

Hi,

On 02/10/2019 07:35:26+0000, [email-masked] wrote:
> +static void wdt_write(struct sam9x60_wdt *wdt, u32 field, u32 val)
> +{
> +	/*
> +	 * WDT_CR and WDT_MR must not be modified within three slow clock
> +	 * periods following a restart of the watchdog performed by a write
> +	 * access in WDT_CR.
> +	 */
> +	while (time_before(jiffies, wdt->last_ping + WDT_DELAY))
> +		usleep_range(30, 125);
> +	writel_relaxed(val, wdt->reg_base + field);
> +	wdt->last_ping = jiffies;
> +}
> +
> +static void wdt_write_nosleep(struct sam9x60_wdt *wdt, u32 field, u32 val)
> +{
> +	if (time_before(jiffies, wdt->last_ping + WDT_DELAY))
> +		usleep_range(123, 250);

So you have a _nosleep function that does sleep?

> +	writel_relaxed(val, wdt->reg_base + field);
> +	wdt->last_ping = jiffies;
> +}
> +
> +static int sam9x60_wdt_start(struct watchdog_device *wdd)
> +{
> +	struct sam9x60_wdt *wdt = watchdog_get_drvdata(wdd);
> +
> +	wdt->mr &= ~AT91_WDT_WDDIS;
> +	wdt_write(wdt, AT91_WDT_MR, wdt->mr);
> +	wdt_write_nosleep(wdt, AT91_WDT_IER, wdt->ir);

I don't think AT91_WDT_IER needs to be protected, you can probably write
it directly. Also, you certainly need to do that before starting the
watchdog to avoid race conditions.

> +
> +	return 0;
> +}
> +
> +static int sam9x60_wdt_stop(struct watchdog_device *wdd)
> +{
> +	struct sam9x60_wdt *wdt = watchdog_get_drvdata(wdd);
> +
> +	wdt->mr |= AT91_WDT_WDDIS;
> +	wdt_write(wdt, AT91_WDT_MR, wdt->mr);
> +	wdt_write_nosleep(wdt, AT91_WDT_IDR, wdt->ir);
> +

I don't think AT91_WDT_IDR needs to be protected.

> +	return 0;
> +}
> +
> +static int sam9x60_wdt_ping(struct watchdog_device *wdd)
> +{
> +	struct sam9x60_wdt *wdt = watchdog_get_drvdata(wdd);
> +
> +	wdt_write(wdt, AT91_WDT_CR, AT91_WDT_KEY | AT91_WDT_WDRSTT);
> +
> +	return 0;
> +}
> +
> +static int sam9x60_wdt_set_timeout(struct watchdog_device *wdd,
> +				   unsigned int timeout)
> +{
> +	struct sam9x60_wdt *wdt = watchdog_get_drvdata(wdd);
> +
> +	wdt_write(wdt, AT91_WDT_WLR,
> +		  AT91_WDT_SET_COUNTER(WDT_SEC2TICKS(timeout)));
> +

I don't think AT91_WDT_WLR needs to be protected.

> +	wdd->timeout = timeout;
> +
> +	return 0;
> +}
> +
> +static const struct watchdog_info sam9x60_wdt_info = {
> +	.options = WDIOF_SETTIMEOUT | WDIOF_MAGICCLOSE | WDIOF_KEEPALIVEPING,
> +	.identity = "Microchip SAM9X60 Watchdog",
> +};
> +
> +static const struct watchdog_ops sam9x60_wdt_ops = {
> +	.owner = THIS_MODULE,
> +	.start = sam9x60_wdt_start,
> +	.stop = sam9x60_wdt_stop,
> +	.ping = sam9x60_wdt_ping,
> +	.set_timeout = sam9x60_wdt_set_timeout,
> +};
> +
> +static irqreturn_t sam9x60_wdt_irq_handler(int irq, void *dev_id)
> +{
> +	struct sam9x60_wdt *wdt = platform_get_drvdata(dev_id);
> +
> +	if (wdt_read(wdt, AT91_WDT_ISR)) {
> +		pr_crit("Microchip Watchdog Software Reset\n");
> +		emergency_restart();
> +		pr_crit("Reboot didn't succeed\n");
> +	}

I'm not really convinced by the software restart use case but I guess it
is to be able to shut down while still flushing data to the storage.
This would not protect against kernel issues then.

> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int of_sam9x60_wdt_init(struct device_node *np, struct sam9x60_wdt *wdt)
> +{
> +	const char *tmp;
> +
> +	wdt->mr = AT91_WDT_WDDIS;
> +
> +	if (!of_property_read_string(np, "atmel,watchdog-type", &tmp) &&
> +	    !strcmp(tmp, "software"))
> +		wdt->ir = AT91_WDT_PERINT;
> +	else
> +		wdt->mr |= AT91_WDT_PERIODRST;
> +
> +	if (of_property_read_bool(np, "atmel,idle-halt"))
> +		wdt->mr |= AT91_WDT_WDIDLEHLT;
> +
> +	if (of_property_read_bool(np, "atmel,dbg-halt"))
> +		wdt->mr |= AT91_WDT_WDDBGHLT;
> +
> +	return 0;
> +}
> +
> +static int sam9x60_wdt_init(struct sam9x60_wdt *wdt)
> +{
> +	u32 reg;
> +	/*
> +	 * When booting and resuming, the bootloader may have changed the
> +	 * watchdog configuration.
> +	 * If the watchdog is already running, we can safely update it.
> +	 * Else, we have to disable it properly.
> +	 */
> +	if (wdt_enabled) {
> +		wdt_write_nosleep(wdt, AT91_WDT_MR, wdt->mr);
> +		wdt_write_nosleep(wdt, AT91_WDT_IER, wdt->ir);
> +		wdt_write(wdt, AT91_WDT_WLR,
> +			  AT91_WDT_SET_COUNTER(WDT_SEC2TICKS(WDT_DEFAULT_TIMEOUT)));
> +
> +	} else {
> +		reg = wdt_read(wdt, AT91_WDT_MR);
> +		if (!(reg & AT91_WDT_WDDIS))
> +			wdt_write_nosleep(wdt, AT91_WDT_MR,
> +					  reg | AT91_WDT_WDDIS);
> +	}
> +	return 0;
> +}
> +
> +static int sam9x60_wdt_probe(struct platform_device *pdev)
> +{
> +	struct watchdog_device *wdd;
> +	struct sam9x60_wdt *wdt;
> +	struct resource *res;
> +	void __iomem *regs;
> +	u32 irq = 0;
> +	int ret;
> +
> +	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
> +	if (!wdt)
> +		return -ENOMEM;
> +
> +	wdd = &wdt->wdd;
> +	wdd->timeout = WDT_DEFAULT_TIMEOUT;
> +	wdd->info = &sam9x60_wdt_info;
> +	wdd->ops = &sam9x60_wdt_ops;
> +	wdd->min_timeout = MIN_WDT_TIMEOUT;
> +	wdd->max_timeout = MAX_WDT_TIMEOUT;
> +	wdt->last_ping = jiffies;
> +
> +	watchdog_set_drvdata(wdd, wdt);
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	regs = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(regs))
> +		return PTR_ERR(regs);
> +
> +	wdt->reg_base = regs;
> +
> +	irq = irq_of_parse_and_map(pdev->dev.of_node, 0);
> +	if (!irq)
> +		dev_warn(&pdev->dev, "failed to get IRQ from DT\n");
> +
> +	ret = of_sam9x60_wdt_init(pdev->dev.of_node, wdt);
> +	if (ret)
> +		return ret;
> +
> +	if ((wdt->ir & AT91_WDT_PERINT) && irq) {
> +		ret = devm_request_irq(&pdev->dev, irq, sam9x60_wdt_irq_handler,
> +				       IRQF_SHARED | IRQF_IRQPOLL |
> +				       IRQF_NO_SUSPEND, pdev->name, pdev);
> +		if (ret) {
> +			dev_err(&pdev->dev,
> +				"cannot register interrupt handler\n");
> +			return ret;
> +		}
> +	}
> +
> +	watchdog_init_timeout(wdd, wdt_timeout, &pdev->dev);
> +
> +	ret = sam9x60_wdt_init(wdt);
> +	if (ret)
> +		return ret;
> +
> +	watchdog_set_nowayout(wdd, nowayout);
> +
> +	ret = watchdog_register_device(wdd);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failed to register watchdog device\n");
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, wdt);
> +
> +	dev_info(&pdev->dev, "initialized (timeout = %d sec, nowayout = %d)\n",
> +		 wdd->timeout, nowayout);
> +
> +	return 0;
> +}
> +
> +static int sam9x60_wdt_remove(struct platform_device *pdev)
> +{
> +	struct sam9x60_wdt *wdt = platform_get_drvdata(pdev);
> +
> +	sam9x60_wdt_stop(&wdt->wdd);
> +
> +	watchdog_unregister_device(&wdt->wdd);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id sam9x60_wdt_of_match[] = {
> +	{ .compatible = "microchip,sam9x60-wdt", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, sam9x60_wdt_of_match);
> +
> +#ifdef CONFIG_PM_SLEEP

Most of the logic has been copy/pasted from sama5d4_wdt.c and this
already miss some improvement that have been made between the time you
copied it and now.

Are you sure both drivers shouldn't be merged? I feel like this will be a
maintenance hell if we don't do that now.

> +static int sam9x60_wdt_resume(struct device *dev)
> +{
> +	struct sam9x60_wdt *wdt = dev_get_drvdata(dev);
> +
> +	/*
> +	 * FIXME: writing MR also pings the watchdog which may not be desired.
> +	 * This should only be done when the registers are lost on suspend but
> +	 * there is no way to get this information right now.
> +	 */
> +	sam9x60_wdt_init(wdt);
> +
> +	return 0;
> +}
> +#endif
> +
> +static SIMPLE_DEV_PM_OPS(sam9x60_wdt_pm_ops, NULL,
> +			 sam9x60_wdt_resume);
> +
> +static struct platform_driver sam9x60_wdt_driver = {
> +	.probe		= sam9x60_wdt_probe,
> +	.remove		= sam9x60_wdt_remove,
> +	.driver		= {
> +		.name	= "sam9x60_wdt",
> +		.pm	= &sam9x60_wdt_pm_ops,
> +		.of_match_table = sam9x60_wdt_of_match,
> +	}
> +};
> +module_platform_driver(sam9x60_wdt_driver);
> +
> +MODULE_AUTHOR("Eugen Hristev");
> +MODULE_DESCRIPTION("Microchip SAM9X60 Watchdog Timer driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.7.4
> 

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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