Date:   Mon, 12 Aug 2019 01:41:22 +0000
From:   Anson Huang <anson.huang@....com>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "otavio@...ystems.com.br" <otavio@...ystems.com.br>,
        Leonard Crestez <leonard.crestez@....com>,
        "schnitzeltony@...il.com" <schnitzeltony@...il.com>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "jan.tuerk@...rion.com" <jan.tuerk@...rion.com>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH 2/4] watchdog: Add i.MX7ULP watchdog support

Hi, Guenter

> On Fri, Aug 09, 2019 at 03:14:00PM +0800, Anson Huang wrote:
> > The i.MX7ULP Watchdog Timer (WDOG) module is an independent timer
> that
> > is available for system use.
> > It provides a safety feature to ensure that software is executing as
> > planned and that the CPU is not stuck in an infinite loop or executing
> > unintended code. If the WDOG module is not serviced
> > (refreshed) within a certain period, it resets the MCU.
> >
> > Add driver support for i.MX7ULP watchdog.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@....com>
> > ---
> >  drivers/watchdog/Kconfig       |  13 +++
> >  drivers/watchdog/Makefile      |   1 +
> >  drivers/watchdog/imx7ulp_wdt.c | 221
> > +++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 235 insertions(+)
> >  create mode 100644 drivers/watchdog/imx7ulp_wdt.c
> >
> > diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig index
> > 8188963..0884e53 100644
> > --- a/drivers/watchdog/Kconfig
> > +++ b/drivers/watchdog/Kconfig
> > @@ -740,6 +740,19 @@ config IMX_SC_WDT
> >  	  To compile this driver as a module, choose M here: the
> >  	  module will be called imx_sc_wdt.
> >
> > +config IMX7ULP_WDT
> > +	tristate "IMX7ULP Watchdog"
> > +	depends on ARCH_MXC || COMPILE_TEST
> > +	select WATCHDOG_CORE
> > +	help
> > +	  This is the driver for the hardware watchdog on the Freescale
> > +	  IMX7ULP and later processors. If you have one of these
> > +	  processors and wish to have watchdog support enabled,
> > +	  say Y, otherwise say N.
> > +
> > +	  To compile this driver as a module, choose M here: the
> > +	  module will be called imx7ulp_wdt.
> > +
> >  config UX500_WATCHDOG
> >  	tristate "ST-Ericsson Ux500 watchdog"
> >  	depends on MFD_DB8500_PRCMU
> > diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> > index 7caa920..7d32537 100644
> > --- a/drivers/watchdog/Makefile
> > +++ b/drivers/watchdog/Makefile
> > @@ -69,6 +69,7 @@ obj-$(CONFIG_TS4800_WATCHDOG) += ts4800_wdt.o
> >  obj-$(CONFIG_TS72XX_WATCHDOG) += ts72xx_wdt.o
> >  obj-$(CONFIG_IMX2_WDT) += imx2_wdt.o
> >  obj-$(CONFIG_IMX_SC_WDT) += imx_sc_wdt.o
> > +obj-$(CONFIG_IMX7ULP_WDT) += imx7ulp_wdt.o
> >  obj-$(CONFIG_UX500_WATCHDOG) += ux500_wdt.o
> >  obj-$(CONFIG_RETU_WATCHDOG) += retu_wdt.o
> >  obj-$(CONFIG_BCM2835_WDT) += bcm2835_wdt.o diff --git
> > a/drivers/watchdog/imx7ulp_wdt.c b/drivers/watchdog/imx7ulp_wdt.c
> new
> > file mode 100644 index 0000000..8d56023
> > --- /dev/null
> > +++ b/drivers/watchdog/imx7ulp_wdt.c
> > @@ -0,0 +1,221 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright 2019 NXP.
> > + */
> > +
> > +#include <linux/init.h>
> > +#include <linux/io.h>
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/reboot.h>
> > +#include <linux/watchdog.h>
> > +
> > +#define WDOG_CS			0x0
> > +#define WDOG_CS_CMD32EN		(1 << 13)
> > +#define WDOG_CS_ULK		(1 << 11)
> > +#define WDOG_CS_RCS		(1 << 10)
> > +#define WDOG_CS_EN		(1 << 7)
> > +#define WDOG_CS_UPDATE		(1 << 5)
> > +
> 
> Please use BIT() where appropriate.

Got it.

> 
> > +#define WDOG_CNT	0x4
> > +#define WDOG_TOVAL	0x8
> > +
> > +#define REFRESH_SEQ0	0xA602
> > +#define REFRESH_SEQ1	0xB480
> > +#define REFRESH		((REFRESH_SEQ1 << 16) | (REFRESH_SEQ0))
> 
> The inner ( ) are unnecessary. While I would accept it for readability for the
> first part, (REFRESH_SEQ0) really doesn't add value.

Got it.

> 
> > +
> > +#define UNLOCK_SEQ0	0xC520
> > +#define UNLOCK_SEQ1	0xD928
> > +#define UNLOCK		((UNLOCK_SEQ1 << 16) | (UNLOCK_SEQ0))
> 
> Same as above.

Got it.

> 
> > +
> > +#define DEFAULT_TIMEOUT 60
> > +#define MAX_TIMEOUT 128
> 
> tabs after _TIMEOUT, please

Got it.

> 
> > +
> > +static bool nowayout = WATCHDOG_NOWAYOUT;
> module_param(nowayout,
> > +bool, 0000); MODULE_PARM_DESC(nowayout, "Watchdog cannot be
> stopped
> > +once started (default="
> > +		 __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
> > +
> > +struct imx7ulp_wdt_device {
> > +	struct notifier_block restart_handler;
> > +	struct watchdog_device wdd;
> > +	void __iomem *base;
> > +	int rate;
> > +};
> > +
> > +static inline void imx7ulp_wdt_enable(void __iomem *base, bool
> > +enable) {
> > +	u32 val = readl(base + WDOG_CS);
> > +
> > +	writel(UNLOCK, base + WDOG_CNT);
> > +	if (enable)
> > +		writel(val | WDOG_CS_EN, base + WDOG_CS);
> > +	else
> > +		writel(val & ~WDOG_CS_EN, base + WDOG_CS); }
> > +
> > +static inline bool imx7ulp_wdt_is_enabled(void __iomem *base) {
> > +	u32 val = readl(base + WDOG_CS);
> > +
> > +	return val & WDOG_CS_EN;
> > +}
> > +
> > +static int imx7ulp_wdt_ping(struct watchdog_device *wdog) {
> > +	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
> > +
> > +	writel(REFRESH, wdt->base + WDOG_CNT);
> > +
> > +	return 0;
> > +}
> > +
> > +static int imx7ulp_wdt_start(struct watchdog_device *wdog) {
> > +	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
> > +
> > +	imx7ulp_wdt_enable(wdt->base, true);
> > +
> > +	return 0;
> > +}
> > +
> > +static int imx7ulp_wdt_stop(struct watchdog_device *wdog) {
> > +	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
> > +
> > +	imx7ulp_wdt_enable(wdt->base, false);
> > +
> > +	return 0;
> > +}
> > +
> > +static int imx7ulp_wdt_set_timeout(struct watchdog_device *wdog,
> > +				   unsigned int timeout)
> > +{
> > +	struct imx7ulp_wdt_device *wdt = watchdog_get_drvdata(wdog);
> > +	u32 val = wdt->rate * timeout;
> > +
> > +	writel(UNLOCK, wdt->base + WDOG_CNT);
> > +	writel(val, wdt->base + WDOG_TOVAL);
> > +
> > +	wdog->timeout = timeout;
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct watchdog_ops imx7ulp_wdt_ops = {
> > +	.owner = THIS_MODULE,
> > +	.start = imx7ulp_wdt_start,
> > +	.stop  = imx7ulp_wdt_stop,
> > +	.ping  = imx7ulp_wdt_ping,
> > +	.set_timeout = imx7ulp_wdt_set_timeout, };
> > +
> > +static const struct watchdog_info imx7ulp_wdt_info = {
> > +	.identity = "i.MX7ULP watchdog timer",
> > +	.options  = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING |
> > +		    WDIOF_MAGICCLOSE,
> > +};
> > +
> > +static inline void imx7ulp_wdt_init(void __iomem *base, unsigned int
> > +timeout) {
> > +	u32 val;
> > +
> > +	/* unlock the wdog for reconfiguration */
> > +	writel_relaxed(UNLOCK_SEQ0, base + WDOG_CNT);
> > +	writel_relaxed(UNLOCK_SEQ1, base + WDOG_CNT);
> > +
> > +	/* set an initial timeout value in TOVAL */
> > +	writel(timeout, base + WDOG_TOVAL);
> > +	/* enable 32bit command sequence and reconfigure */
> > +	val = (1 << 13) | (1 << 8) | (1 << 5);
> 
> Please use BIT()

Got it.

> 
> > +	writel(val, base + WDOG_CS);
> > +}
> > +
> > +static int imx7ulp_wdt_probe(struct platform_device *pdev) {
> > +	struct imx7ulp_wdt_device *imx7ulp_wdt;
> > +	struct device *dev = &pdev->dev;
> > +	struct watchdog_device *wdog;
> > +	int ret;
> > +
> > +	imx7ulp_wdt = devm_kzalloc(&pdev->dev,
> > +				   sizeof(*imx7ulp_wdt), GFP_KERNEL);
> > +	if (!imx7ulp_wdt)
> > +		return -ENOMEM;
> > +
> > +	platform_set_drvdata(pdev, imx7ulp_wdt);
> > +
> > +	imx7ulp_wdt->base = devm_platform_ioremap_resource(pdev, 0);
> > +	if (IS_ERR(imx7ulp_wdt->base))
> > +		return PTR_ERR(imx7ulp_wdt->base);
> > +
> > +	imx7ulp_wdt->rate = 1000;
> > +	wdog = &imx7ulp_wdt->wdd;
> > +	wdog->info = &imx7ulp_wdt_info;
> > +	wdog->ops = &imx7ulp_wdt_ops;
> > +	wdog->min_timeout = 1;
> > +	wdog->max_timeout = MAX_TIMEOUT;
> > +	wdog->parent = dev;
> > +	wdog->timeout = DEFAULT_TIMEOUT;
> > +
> > +	watchdog_init_timeout(wdog, 0, dev);
> > +	watchdog_stop_on_reboot(wdog);
> > +	watchdog_stop_on_unregister(wdog);
> > +	watchdog_set_drvdata(wdog, imx7ulp_wdt);
> > +	imx7ulp_wdt_init(imx7ulp_wdt->base, wdog->timeout *
> > +imx7ulp_wdt->rate);
> > +
> > +	ret = devm_watchdog_register_device(dev, wdog);
> > +	if (ret)
> > +		dev_err(dev, "Failed to register watchdog device\n");
> 
> An error message is already displayed by the watchdog core.

Got it.

> 
> > +
> > +	return ret;
> > +}
> > +
> > +static int __maybe_unused imx7ulp_wdt_suspend(struct device *dev) {
> > +	struct imx7ulp_wdt_device *imx7ulp_wdt = dev_get_drvdata(dev);
> > +
> > +	if (watchdog_active(&imx7ulp_wdt->wdd))
> > +		imx7ulp_wdt_stop(&imx7ulp_wdt->wdd);
> > +
> > +	return 0;
> > +}
> > +
> > +static int __maybe_unused imx7ulp_wdt_resume(struct device *dev) {
> > +	struct imx7ulp_wdt_device *imx7ulp_wdt = dev_get_drvdata(dev);
> > +	u32 timeout = imx7ulp_wdt->wdd.timeout * imx7ulp_wdt->rate;
> > +
> > +	if (imx7ulp_wdt_is_enabled(imx7ulp_wdt->base))
> > +		imx7ulp_wdt_init(imx7ulp_wdt->base, timeout);
> > +
> If I understand correctly, imx7ulp_wdt_is_enabled() returns true if the
> watchdog is running. Since it was stopped on suspend, that means that it was
> started in BIOS/rommon during resume.
> 
> With that, the above translates to "If the watchdog was started by
> BIOS/rommon, re-initialize it. Otherwise do nothing". This doesn't really
> make much sense to me. What if the watchdog was reprogrammed by the
> BIOS/rommon, but not started ? In other words, why not call
> imx7ulp_wdt_init() unconditionally ?

The i.MX7ULP hardware design is, if A7 domain is powered off during suspend (mem suspend),
watchdog will be always reset and re-started by boot ROM. If A7 domain is NOT powered off during
suspend (standby suspend), the watchdog does NOT lose context and boot ROM NOT
run again after resume. 

> 
> Also, if it is possible that the watchdog is started by BIOS/rommon, why not
> keep it enabled and tell the watchdog core about it in the probe function ?

There are 2 cases of watchdog status during suspend/resume, i.MX7ULP supports
both standby suspend and mem suspend, for mem suspend, the whole A7 domain
will be powered off, and after resume, watchdog will be re-started by boot ROM (BIOS),
while for standby suspend, the watchdog does NOT re-started by boot ROM, as A7
domain is NOT powered off. That is why I added the check here, since there are 2 cases
sharing same suspend/resume callback. Does it make sense to you?

Thanks,
Anson

> 
> > +	if (watchdog_active(&imx7ulp_wdt->wdd))
> > +		imx7ulp_wdt_start(&imx7ulp_wdt->wdd);
> > +
> > +	return 0;
> > +}
> > +
> > +static SIMPLE_DEV_PM_OPS(imx7ulp_wdt_pm_ops,
> imx7ulp_wdt_suspend,
> > +			 imx7ulp_wdt_resume);
> > +
> > +static const struct of_device_id imx7ulp_wdt_dt_ids[] = {
> > +	{ .compatible = "fsl,imx7ulp-wdt", },
> > +	{ /* sentinel */ }
> > +};
> > +MODULE_DEVICE_TABLE(of, imx7ulp_wdt_dt_ids);
> > +
> > +static struct platform_driver imx7ulp_wdt_driver = {
> > +	.probe		= imx7ulp_wdt_probe,
> > +	.driver		= {
> > +		.name	= "imx7ulp-wdt",
> > +		.pm	= &imx7ulp_wdt_pm_ops,
> > +		.of_match_table = imx7ulp_wdt_dt_ids,
> > +	},
> > +};
> > +module_platform_driver(imx7ulp_wdt_driver);
> > +
> > +MODULE_AUTHOR("Anson Huang <Anson.Huang@....com>");
> > +MODULE_DESCRIPTION("Freescale i.MX7ULP watchdog driver");
> > +MODULE_LICENSE("GPL v2");
> > --
> > 2.7.4
> >

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