Re: [PATCH 2/2] watchdog: digicolor: driver for Conexant Digicolor CX92755 SoC

From: Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>
To: Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org>,
	Wim Van Sebroeck <wim-IQzOog9fTRqzQB+pC5nmwQ@public.gmane.org>
Cc: linux-watchdog-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
Subject: Re: [PATCH 2/2] watchdog: digicolor: driver for Conexant Digicolor CX92755 SoC
Date: Sun, 22 Mar 2015 09:59:06 -0700	[thread overview]
Message-ID: <550EF4DA.6040407@roeck-us.net> (raw)
In-Reply-To: <409ece75204d3911dc526a9bc0c908fc30893b26.1427028036.git.baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org>

On 03/22/2015 05:40 AM, Baruch Siach wrote:
> This commit add a driver for the watchdog functionality of the Conexant CX92755
> SoC, from the Digicolor series of SoCs. Of 8 system timers provided by the
> CX92755, the first one, timer A, can reset the chip when its counter reaches
> zero. This driver uses this capability to provide userspace with a standard
> watchdog, using the watchdog timer driver core framework. This driver also
> implements a reboot handler for the reboot(2) system call.
>
> The watchdog driver shares the timer registers with the CX92755 timer driver
> (drivers/clocksource/timer-digicolor.c). The timer driver, however, uses only
> timers other than A, so both drivers should coexist.
>
> Signed-off-by: Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org>

Looks pretty good. Couple of comments below.

Thanks,
Guenter

> ---
>   drivers/watchdog/Kconfig         |  10 ++
>   drivers/watchdog/Makefile        |   1 +
>   drivers/watchdog/digicolor_wdt.c | 203 +++++++++++++++++++++++++++++++++++++++
>   3 files changed, 214 insertions(+)
>   create mode 100644 drivers/watchdog/digicolor_wdt.c
>
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index 16f202350997..7d73d6c78cf6 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -515,6 +515,16 @@ config MEDIATEK_WATCHDOG
>   	  To compile this driver as a module, choose M here: the
>   	  module will be called mtk_wdt.
>
> +config DIGICOLOR_WATCHDOG
> +	tristate "Conexant Digicolor SoCs watchdog support"
> +	depends on ARCH_DIGICOLOR
> +	select WATCHDOG_CORE

This doesn't (directly) depend on HAVE_CLK, meaning clk_get can return NULL
if HAVE_CLK is not configured. Can that happen ?

> +	help
> +	  Say Y here to include support for the watchdog timer
> +	  in Conexant Digicolor SoCs.
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called digicolor_wdt.
> +
>   # AVR32 Architecture
>
>   config AT32AP700X_WDT
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index 5c19294d1c30..0721f10e8d13 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -64,6 +64,7 @@ obj-$(CONFIG_BCM_KONA_WDT) += bcm_kona_wdt.o
>   obj-$(CONFIG_TEGRA_WATCHDOG) += tegra_wdt.o
>   obj-$(CONFIG_MESON_WATCHDOG) += meson_wdt.o
>   obj-$(CONFIG_MEDIATEK_WATCHDOG) += mtk_wdt.o
> +obj-$(CONFIG_DIGICOLOR_WATCHDOG) += digicolor_wdt.o
>
>   # AVR32 Architecture
>   obj-$(CONFIG_AT32AP700X_WDT) += at32ap700x_wdt.o
> diff --git a/drivers/watchdog/digicolor_wdt.c b/drivers/watchdog/digicolor_wdt.c
> new file mode 100644
> index 000000000000..260cc4495370
> --- /dev/null
> +++ b/drivers/watchdog/digicolor_wdt.c
> @@ -0,0 +1,203 @@
> +/*
> + * Watchdog driver for Conexant Digicolor
> + *
> + * Copyright (C) 2015 Paradox Innovation Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the
> + * Free Software Foundation; either version 2 of the License, or (at your
> + * option) any later version.
> + */
> +
> +#include <linux/types.h>
> +#include <linux/module.h>
> +#include <linux/io.h>
> +#include <linux/delay.h>
> +#include <linux/clk.h>
> +#include <linux/watchdog.h>
> +#include <linux/reboot.h>
> +#include <linux/platform_device.h>
> +#include <linux/of_address.h>
> +
> +#define TIMER_A_CONTROL		0
> +#define TIMER_A_COUNT		4
> +
> +#define TIMER_A_ENABLE_COUNT	BIT(0)
> +#define TIMER_A_ENABLE_WATCHDOG	BIT(1)
> +
> +#define DC_WDT_DEFAULT_TIME	5
> +

Five seconds is an extremely low default timeout. More common would be
30 or 60 seconds. Any special reason for selecting this default ?

> +struct dc_wdt {
> +	void __iomem		*base;
> +	struct clk		*clk;
> +	struct notifier_block	restart_handler;
> +	spinlock_t		lock;
> +};
> +
> +static unsigned timeout;
> +module_param(timeout, uint, 0);
> +MODULE_PARM_DESC(timeout, "Watchdog timeout in seconds");
> +
> +static int dc_restart_handler(struct notifier_block *this, unsigned long mode,
> +			      void *cmd)
> +{
> +	struct dc_wdt *wdt = container_of(this, struct dc_wdt, restart_handler);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&wdt->lock, flags);
> +
> +	writel_relaxed(0, wdt->base + TIMER_A_CONTROL);
> +	writel_relaxed(1, wdt->base + TIMER_A_COUNT);
> +	writel_relaxed(TIMER_A_ENABLE_COUNT | TIMER_A_ENABLE_WATCHDOG,
> +		       wdt->base + TIMER_A_CONTROL);
> +
> +	spin_unlock_irqrestore(&wdt->lock, flags);
> +
> +	/* wait for reset to assert... */
> +	mdelay(500);
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static int dc_wdt_start(struct watchdog_device *wdog)
> +{
> +	struct dc_wdt *wdt = watchdog_get_drvdata(wdog);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&wdt->lock, flags);
> +
> +	writel_relaxed(0, wdt->base + TIMER_A_CONTROL);
> +	writel_relaxed(wdog->timeout * clk_get_rate(wdt->clk),
> +		       wdt->base + TIMER_A_COUNT);
> +	writel_relaxed(TIMER_A_ENABLE_COUNT | TIMER_A_ENABLE_WATCHDOG,
> +		       wdt->base + TIMER_A_CONTROL);
> +
> +	spin_unlock_irqrestore(&wdt->lock, flags);
> +
You have this sequence twice, so a little helper function taking
wdt and the timeout as parameters might be useful.

> +	return 0;
> +}
> +
> +static int dc_wdt_stop(struct watchdog_device *wdog)
> +{
> +	struct dc_wdt *wdt = watchdog_get_drvdata(wdog);
> +
> +	writel_relaxed(0, wdt->base + TIMER_A_CONTROL);
> +
> +	return 0;
> +}
> +
> +static int dc_wdt_set_timeout(struct watchdog_device *wdog, unsigned int t)
> +{
> +	wdog->timeout = t;
> +
No updating the timer count register ?

If you increase the timeout significantly, the next ping may come too late.

> +	return 0;
> +}
> +
> +static unsigned int dc_wdt_get_timeleft(struct watchdog_device *wdog)
> +{
> +	struct dc_wdt *wdt = watchdog_get_drvdata(wdog);
> +	uint32_t count = readl_relaxed(wdt->base + TIMER_A_COUNT);
> +
> +	return (count / clk_get_rate(wdt->clk));
> +}
> +
> +static struct watchdog_ops dc_wdt_ops = {
> +	.owner		= THIS_MODULE,
> +	.start		= dc_wdt_start,
> +	.stop		= dc_wdt_stop,

Since you don't have a ping function, each ping will stop the watchdog,
update the timer, and restart it. Is this intentional ?

> +	.set_timeout	= dc_wdt_set_timeout,
> +	.get_timeleft	= dc_wdt_get_timeleft,
> +};
> +
> +static struct watchdog_info dc_wdt_info = {
> +	.options	= WDIOF_SETTIMEOUT | WDIOF_MAGICCLOSE
> +			| WDIOF_KEEPALIVEPING,
> +	.identity	= "Conexant Digicolor Watchdog",
> +};
> +
> +static struct watchdog_device dc_wdt_wdd = {
> +	.info		= &dc_wdt_info,
> +	.ops		= &dc_wdt_ops,
> +	.min_timeout	= 1,
> +	.timeout	= DC_WDT_DEFAULT_TIME,
> +};
> +
> +static int dc_wdt_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device_node *np = dev->of_node;
> +	struct dc_wdt *wdt;
> +	int ret;
> +
> +	wdt = devm_kzalloc(dev, sizeof(struct dc_wdt), GFP_KERNEL);
> +	if (!wdt)
> +		return -ENOMEM;
> +	platform_set_drvdata(pdev, wdt);
> +
> +	wdt->base = of_iomap(np, 0);
> +	if (!wdt->base) {
> +		dev_err(dev, "Failed to remap watchdog regs");
> +		return -ENODEV;
> +	}
> +
> +	wdt->clk = clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(wdt->clk))
> +		return PTR_ERR(wdt->clk);

iounmap missing.

> +	dc_wdt_wdd.max_timeout = U32_MAX / clk_get_rate(wdt->clk);
> +
> +	spin_lock_init(&wdt->lock);
> +
> +	watchdog_set_drvdata(&dc_wdt_wdd, wdt);
> +	watchdog_init_timeout(&dc_wdt_wdd, timeout, dev);
> +	ret = watchdog_register_device(&dc_wdt_wdd);
> +	if (ret) {
> +		dev_err(dev, "Failed to register watchdog device");
> +		iounmap(wdt->base);

I don't see clk_put in any of the error cases. How about using devm_clk_get above ?

> +		return ret;
> +	}
> +
> +	wdt->restart_handler.notifier_call = dc_restart_handler;
> +	wdt->restart_handler.priority = 128;

Is 128 intentional, ie is this the expected reset method for this platform ?
If not, it may be better to select a lower priority (eg 64). Using a watchdog
to reset a system should in general be a method of last resort.

> +	ret = register_restart_handler(&wdt->restart_handler);
> +	if (ret)
> +		dev_err(&pdev->dev, "cannot register restart handler\n");

dev_warn would be better here, since this is non-fatal.

> +
> +	return 0;
> +}
> +
> +static int dc_wdt_remove(struct platform_device *pdev)
> +{
> +	struct dc_wdt *wdt = platform_get_drvdata(pdev);
> +
> +	unregister_restart_handler(&wdt->restart_handler);
> +	watchdog_unregister_device(&dc_wdt_wdd);
> +	iounmap(wdt->base);

clk_put missing (or use devm_clk_get).

> +
> +	return 0;
> +}
> +
> +static void dc_wdt_shutdown(struct platform_device *pdev)
> +{
> +	dc_wdt_stop(&dc_wdt_wdd);
> +}
> +
> +static const struct of_device_id dc_wdt_of_match[] = {
> +	{ .compatible = "cnxt,cx92755-wdt", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, dc_wdt_of_match);
> +
> +static struct platform_driver dc_wdt_driver = {
> +	.probe		= dc_wdt_probe,
> +	.remove		= dc_wdt_remove,
> +	.shutdown	= dc_wdt_shutdown,
> +	.driver = {
> +		.name =		"digicolor-wdt",
> +		.of_match_table = dc_wdt_of_match,
> +	},
> +};
> +module_platform_driver(dc_wdt_driver);
> +
> +MODULE_AUTHOR("Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org>");
> +MODULE_DESCRIPTION("Driver for Conexant Digicolor watchdog timer");
> +MODULE_LICENSE("GPL");
>

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