[PATCH 1/2] watchdog: digicolor: document device tree binding

[PATCH 1/2] watchdog: digicolor: document device tree binding

[Baruch Siach]

Add a device tree binding documentation to the watchdog hardware block on the
Conexant CX92755 SoC. The CX92755 is from the Digicolor SoCs series. Other SoCs
in that series may share the same hardware block.

Signed-off-by: Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org>
---
 .../devicetree/bindings/watchdog/digicolor-wdt.txt | 25 ++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/watchdog/digicolor-wdt.txt

diff --git a/Documentation/devicetree/bindings/watchdog/digicolor-wdt.txt b/Documentation/devicetree/bindings/watchdog/digicolor-wdt.txt
new file mode 100644
index 000000000000..a882967e17d4
--- /dev/null
+++ b/Documentation/devicetree/bindings/watchdog/digicolor-wdt.txt
@@ -0,0 +1,25 @@
+Conexant Digicolor SoCs Watchdog timer
+
+The watchdog functionality in Conexant Digicolor SoCs relies on the so called
+"Agent Communication" block. This block includes the eight programmable system
+timer counters. The first timer (called "Timer A") is the only one that can be
+used as watchdog.
+
+Required properties:
+
+- compatible : Should be "cnxt,cx92755-wdt"
+- reg : Specifies base physical address and size of the registers
+- clocks : phandle; specifies the clock that drives the timer
+
+Optional properties:
+
+- timeout-sec : Contains the watchdog timeout in seconds
+
+Example:
+
+	watchdog@f0000fc0 {
+		compatible = "cnxt,cx92755-wdt";
+		reg = <0xf0000fc0 0x8>;
+		clocks = <&main_clk>;
+		timeout-sec = <15>;
+	};
-- 
2.1.4

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

[Baruch Siach]

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>
---
 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
+	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
+
+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);
+
+	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;
+
+	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,
+	.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);
+	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);
+		return ret;
+	}
+
+	wdt->restart_handler.notifier_call = dc_restart_handler;
+	wdt->restart_handler.priority = 128;
+	ret = register_restart_handler(&wdt->restart_handler);
+	if (ret)
+		dev_err(&pdev->dev, "cannot register restart handler\n");
+
+	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);
+
+	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");
-- 
2.1.4

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

[Guenter Roeck]

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

[Baruch Siach]

Hi Guenter,

On Sun, Mar 22, 2015 at 09:59:06AM -0700, Guenter Roeck wrote:
> 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. Please see my responses below.

> >  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 ?

ARCH_DIGICOLOR depends on ARCH_MULTI_V7 which depends on ARCH_MULTIPLATFORM, 
which in turn selects COMMON_CLK. So using the clk API should be safe.

[...]

> >+#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 ?

I copied this value from an old Conexant provided watchdog driver, so I 
thought it should be a safe default. In fact, the RTC timer is clocked at 
200MHz by default, and since the counter is only 32bit wide, we can't set 
timeout much longer than 20 seconds anyway.

[...]

> >+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.

Right. Will do.

> >+	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.

Some other drivers are doing the same (e.g. bcm2835_wdt, orion_wdt). Are they 
buggy? Will fix, anyway.

> >+	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 ?

No. Just copied other drivers. I guess I can set .ping to dc_wdt_start as 
well.

[...]

> >+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.

Will fix.

> >+	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 ?

Will fix.

> 
> >+		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.

Copied this value from imx2_wdt. grep indicates that almost all other watchdog 
drivers implementing restart_handler use priority of 128 (except bcm47xx_wdt). 
What is the policy here?

> 
> >+	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.

Again, copied from imx2_wdt. But I'll fix that anyway.

> >+	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).

Will fix.

Thanks for reviewing.

baruch

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

[Guenter Roeck]

On 03/22/2015 11:08 AM, Baruch Siach wrote:
> Hi Guenter,
>
> On Sun, Mar 22, 2015 at 09:59:06AM -0700, Guenter Roeck wrote:
>> 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. Please see my responses below.
>
>>>   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 ?
>
> ARCH_DIGICOLOR depends on ARCH_MULTI_V7 which depends on ARCH_MULTIPLATFORM,
> which in turn selects COMMON_CLK. So using the clk API should be safe.
>
> [...]
>
>>> +#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 ?
>
> I copied this value from an old Conexant provided watchdog driver, so I
> thought it should be a safe default. In fact, the RTC timer is clocked at
> 200MHz by default, and since the counter is only 32bit wide, we can't set
> timeout much longer than 20 seconds anyway.
>
That really depends on the application, user space load, and watchdogd
application configuration.

You declare that since someone else is doing it in a different watchdog
driver, it is safe to do it here. This is not really a good argument.

Remember we are talking about the default setting here, not about some
target specific setting. I would have thought that the default setting
would be on the relaxed side of the timeout (probably actually the
maximum if the maximum is in the 20 seconds range), not a low limit.
After all, it is always possible to overwrite a relaxed value with a
stricter one. Overwriting a strict value with a more relaxed one may
be more difficult if the application handling the watchdog doesn't
start in time to prevent the first timeout from happening.

Anyway, I am fine if you think that 5 seconds is ok; that is really
your call to make. But I really think your logic should be a bit better
than "someone else is doing it as well".

> [...]
>
>>> +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.
>
> Right. Will do.
>
>>> +	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.
>
> Some other drivers are doing the same (e.g. bcm2835_wdt, orion_wdt). Are they
> buggy? Will fix, anyway.
>

I always like that kind of argument ;-). Others do it, therefore I can do it as well.

Why don't you give it a try.

Here is the logic: Say, you increase the timeout from 5 seconds to 20 seconds.
User space now believes it has to ping the watchdog every 10 seconds or so.
However, you did not update the HW timeout immediately, meaning the watchdog will
time out no later than 5 seconds after the timeout change, even thought the timeout
is now supposed to be 20 seconds. If user space does not ping the watchdog immediately
after changing the timeout, but starts using the 10-second ping schedule, you may
have a problem.

Sure, you can declare that you expect user space to ping the watchdog immediately
after changing the timeout, but that does not necessarily happen just because
you expect it to happen.

>>> +	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 ?
>
> No. Just copied other drivers. I guess I can set .ping to dc_wdt_start as
> well.
>
That would be pretty pointless, since the watchdog core calls the start
function if no ping function is available.

Other hardware may mandate the sequence (turn off watchdog, set timer,
turn on watchdog). Other driver developers may have used the sequence
for convenience. That doesn't mean that this watchdog driver should use
the same sequence or logic just because others do it.

Specific problem: Assume your system hangs itself hard just after the
watchdog is disabled, due to some other CPU core doing something really
bad. Oops ... no more watchdog, system is dead.

Sure, this may be the mandated sequence on this architecture. That would be
bad enough, since it leaves the system unprotected for a couple of instructions
every few seconds. That doesn't mean it should be the default behavior,
though, if the sequence is _not_ mandated by the hardware.

So, if your argument was that the hardware mandates the sequence, fine,
nothing we can do about it. Yet, your argument is that you do it because
others do it. Think about it.

> [...]
>
>>> +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.
>
> Will fix.
>
>>> +	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 ?
>
> Will fix.
>
>>
>>> +		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.
>
> Copied this value from imx2_wdt. grep indicates that almost all other watchdog
> drivers implementing restart_handler use priority of 128 (except bcm47xx_wdt).
> What is the policy here?
>

The policy is to do what is sensible for the platform. That can only be decided
on a case-by-case basis. The documentation suggests to use 128 for "Default restart
handler; use if no other restart handler is expected to be available, and/or if
restart functionality is sufficient to restart the entire system".

So if this is the only means expected to be available to reset the system
for this architecture/platform, and if the watchdog resets the entire system
(not just the CPU), 128 may be ok to use. If, however, there may be other
means to reset the system, such as a GPIO pin, maybe not.

Thanks,
Guenter

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

[Baruch Siach]

Hi Guenter,

On Sun, Mar 22, 2015 at 11:59:43AM -0700, Guenter Roeck wrote:
> On 03/22/2015 11:08 AM, Baruch Siach wrote:
> >On Sun, Mar 22, 2015 at 09:59:06AM -0700, Guenter Roeck wrote:
> >>On 03/22/2015 05:40 AM, Baruch Siach wrote:
> >>>+#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 ?
> >
> >I copied this value from an old Conexant provided watchdog driver, so I
> >thought it should be a safe default. In fact, the RTC timer is clocked at
> >200MHz by default, and since the counter is only 32bit wide, we can't set
> >timeout much longer than 20 seconds anyway.
>
> That really depends on the application, user space load, and watchdogd
> application configuration.
> 
> You declare that since someone else is doing it in a different watchdog
> driver, it is safe to do it here. This is not really a good argument.
> 
> Remember we are talking about the default setting here, not about some
> target specific setting. I would have thought that the default setting
> would be on the relaxed side of the timeout (probably actually the
> maximum if the maximum is in the 20 seconds range), not a low limit.
> After all, it is always possible to overwrite a relaxed value with a
> stricter one. Overwriting a strict value with a more relaxed one may
> be more difficult if the application handling the watchdog doesn't
> start in time to prevent the first timeout from happening.
> 
> Anyway, I am fine if you think that 5 seconds is ok; that is really
> your call to make. But I really think your logic should be a bit better
> than "someone else is doing it as well".

My intention was to minimize the surprise for someone migrating from the old 
Conexant provided kernel to mainline. I agree though that this logic does not 
extend to watchdog timeout default. I'll set the default to (U32_MAX / 
clk_rate).

[...]

> >>>+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.
> >
> >Some other drivers are doing the same (e.g. bcm2835_wdt, orion_wdt). Are they
> >buggy? Will fix, anyway.
> >
> 
> I always like that kind of argument ;-). Others do it, therefore I can do it as well.
> 
> Why don't you give it a try.
> 
> Here is the logic: Say, you increase the timeout from 5 seconds to 20 seconds.
> User space now believes it has to ping the watchdog every 10 seconds or so.
> However, you did not update the HW timeout immediately, meaning the watchdog will
> time out no later than 5 seconds after the timeout change, even thought the timeout
> is now supposed to be 20 seconds. If user space does not ping the watchdog immediately
> after changing the timeout, but starts using the 10-second ping schedule, you may
> have a problem.
> 
> Sure, you can declare that you expect user space to ping the watchdog immediately
> after changing the timeout, but that does not necessarily happen just because
> you expect it to happen.

OK. Will fix.

> >>>+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 ?
> >
> >No. Just copied other drivers. I guess I can set .ping to dc_wdt_start as
> >well.
> >
> That would be pretty pointless, since the watchdog core calls the start
> function if no ping function is available.
> 
> Other hardware may mandate the sequence (turn off watchdog, set timer,
> turn on watchdog). Other driver developers may have used the sequence
> for convenience. That doesn't mean that this watchdog driver should use
> the same sequence or logic just because others do it.
> 
> Specific problem: Assume your system hangs itself hard just after the
> watchdog is disabled, due to some other CPU core doing something really
> bad. Oops ... no more watchdog, system is dead.
> 
> Sure, this may be the mandated sequence on this architecture. That would be
> bad enough, since it leaves the system unprotected for a couple of instructions
> every few seconds. That doesn't mean it should be the default behavior,
> though, if the sequence is _not_ mandated by the hardware.
> 
> So, if your argument was that the hardware mandates the sequence, fine,
> nothing we can do about it. Yet, your argument is that you do it because
> others do it. Think about it.

Right. Unfortunately in this case the counter can only be programmed when the 
timer is off. The watchdog hardware functionality (a single bit, actually) 
looks like an afterthought addition to the system timer. The fact that timer 
update takes place under spinlock should mitigate the problem somewhat.

[...]

> >>>+	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.
> >
> >Copied this value from imx2_wdt. grep indicates that almost all other watchdog
> >drivers implementing restart_handler use priority of 128 (except bcm47xx_wdt).
> >What is the policy here?
> 
> The policy is to do what is sensible for the platform. That can only be decided
> on a case-by-case basis. The documentation suggests to use 128 for "Default restart
> handler; use if no other restart handler is expected to be available, and/or if
> restart functionality is sufficient to restart the entire system".
> 
> So if this is the only means expected to be available to reset the system
> for this architecture/platform, and if the watchdog resets the entire system
> (not just the CPU), 128 may be ok to use. If, however, there may be other
> means to reset the system, such as a GPIO pin, maybe not.

This driver is for a SoC hardware block. The restart_handler priority level is 
hard coded in the drivers, and should thus work reasonably well for all its 
users. The fact that the common priority level is 128, is significant in this 
case IMO (as apposed to issues discussed above). Systems designers are likely 
take this priority level into account in their designs. If this does not match 
the documentation, then documentation needs to change to reflect reality.

Thanks for your thorough review, and enlightening comments.

baruch

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

[Guenter Roeck]

On 03/22/2015 10:33 PM, Baruch Siach wrote:

> [...]
>
>>>>> +	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.
>>>
>>> Copied this value from imx2_wdt. grep indicates that almost all other watchdog
>>> drivers implementing restart_handler use priority of 128 (except bcm47xx_wdt).
>>> What is the policy here?
>>
>> The policy is to do what is sensible for the platform. That can only be decided
>> on a case-by-case basis. The documentation suggests to use 128 for "Default restart
>> handler; use if no other restart handler is expected to be available, and/or if
>> restart functionality is sufficient to restart the entire system".
>>
>> So if this is the only means expected to be available to reset the system
>> for this architecture/platform, and if the watchdog resets the entire system
>> (not just the CPU), 128 may be ok to use. If, however, there may be other
>> means to reset the system, such as a GPIO pin, maybe not.
>
> This driver is for a SoC hardware block. The restart_handler priority level is
> hard coded in the drivers, and should thus work reasonably well for all its
> users. The fact that the common priority level is 128, is significant in this
> case IMO (as apposed to issues discussed above). Systems designers are likely
> take this priority level into account in their designs. If this does not match
> the documentation, then documentation needs to change to reflect reality.
>
Seems to me you are arguing (again) that it is ok to use priority 128 not
because of merit, but because others do it as well. As you may have noticed,
I kind of dislike that line of argument. Actually, I don't consider it to be
a valid argument in the first place.

Guenter

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

[Baruch Siach]

Hi Guenter,

Adding LKML to Cc.

On Sun, Mar 22, 2015 at 10:50:28PM -0700, Guenter Roeck wrote:
> On 03/22/2015 10:33 PM, Baruch Siach wrote:
> >>>>>+	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.
> >>>
> >>>Copied this value from imx2_wdt. grep indicates that almost all other watchdog
> >>>drivers implementing restart_handler use priority of 128 (except bcm47xx_wdt).
> >>>What is the policy here?
> >>
> >>The policy is to do what is sensible for the platform. That can only be decided
> >>on a case-by-case basis. The documentation suggests to use 128 for "Default restart
> >>handler; use if no other restart handler is expected to be available, and/or if
> >>restart functionality is sufficient to restart the entire system".
> >>
> >>So if this is the only means expected to be available to reset the system
> >>for this architecture/platform, and if the watchdog resets the entire system
> >>(not just the CPU), 128 may be ok to use. If, however, there may be other
> >>means to reset the system, such as a GPIO pin, maybe not.
> >
> >This driver is for a SoC hardware block. The restart_handler priority level is
> >hard coded in the drivers, and should thus work reasonably well for all its
> >users. The fact that the common priority level is 128, is significant in this
> >case IMO (as apposed to issues discussed above). Systems designers are likely
> >take this priority level into account in their designs. If this does not match
> >the documentation, then documentation needs to change to reflect reality.
>
> Seems to me you are arguing (again) that it is ok to use priority 128 not
> because of merit, but because others do it as well. As you may have noticed,
> I kind of dislike that line of argument. Actually, I don't consider it to be
> a valid argument in the first place.

I fully agree with you on other cases as I acknowledged earlier, but I 
disagree here. The only merit of priority 128 is how it is accepted. This 
priority level has no technical significance in or by itself. Our only 
guidance for choosing the "right" level is what others do. That's my opinion, 
at least.

At the technical level, this watchdog indirectly generates an external reset 
signal that should be used to reset the entire system. This seems to be the 
case on the Equinox evaluation board, which is the system I test this driver 
on. I believe this conforms to the documented behaviour for the 128 priority 
level.

baruch

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