Date:	Fri, 5 Sep 2014 08:58:11 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel@...inux.com, wim@...ana.be, linux-watchdog@...r.kernel.org,
	David Paris <david.paris@...com>
Subject: Re: [PATCH 4/4] watchdog: st_wdt: Add new driver for ST's LPC
 Watchdog

On Thu, Sep 04, 2014 at 03:39:52PM +0100, Lee Jones wrote:

Some text may be useful here.

> Signed-off-by: David Paris <david.paris@...com>
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  drivers/watchdog/Kconfig  |  16 +++
>  drivers/watchdog/Makefile |   1 +
>  drivers/watchdog/st_wdt.c | 314 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 331 insertions(+)
>  create mode 100644 drivers/watchdog/st_wdt.c
> 
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index f57312f..c8abf57 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -432,6 +432,22 @@ config SIRFSOC_WATCHDOG
>  	  Support for CSR SiRFprimaII and SiRFatlasVI watchdog. When
>  	  the watchdog triggers the system will be reset.
>  
> +config ST_WATCHDOG
> +       tristate "STMicroelectronics LPC Watchdog"
> +       depends on ARCH_STI && OF
> +       depends on !RTC_DRV_ST_LPC
> +       select WATCHDOG_CORE
> +       help
> +	 Say Y here to include Watchdog timer support for the watchdog
> +	 existing in the LPC of STMicroelectronics SOCs.
> +	 !!! BE CARREFUL !!!
> +	 This driver shares hardware resources with RTC Alarm part of the
> +	 LPC. Both LPC Watchdog driver and LPC RTC driver cannot be
> +	 used together.
> +
Is this mandatory or an implementation choice ?
Or, in other words, could the resources be shared among drivers ?

> +	 To compile this driver as a module, choose M here: the
> +	 module will be called st-wdt.
> +
>  config TEGRA_WATCHDOG
>  	tristate "Tegra watchdog"
>  	depends on ARCH_TEGRA || COMPILE_TEST
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index 468c320..eb19937 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -57,6 +57,7 @@ obj-$(CONFIG_RETU_WATCHDOG) += retu_wdt.o
>  obj-$(CONFIG_BCM2835_WDT) += bcm2835_wdt.o
>  obj-$(CONFIG_MOXART_WDT) += moxart_wdt.o
>  obj-$(CONFIG_SIRFSOC_WATCHDOG) += sirfsoc_wdt.o
> +obj-$(CONFIG_ST_WATCHDOG) += st_wdt.o
>  obj-$(CONFIG_BCM_KONA_WDT) += bcm_kona_wdt.o
>  obj-$(CONFIG_TEGRA_WATCHDOG) += tegra_wdt.o
>  
> diff --git a/drivers/watchdog/st_wdt.c b/drivers/watchdog/st_wdt.c
> new file mode 100644
> index 0000000..b5dbc7d
> --- /dev/null
> +++ b/drivers/watchdog/st_wdt.c
> @@ -0,0 +1,314 @@
> +/*
> + * st-wdt.c -- ST's LPC Watchdog
> + *
> + * Copyright (C) 2014 STMicroelectronics -- All Rights Reserved
> + *
> + * Author: David Paris <david.paris@...com> for STMicroelectronics
> + * Contributor: Lee Jones <lee.jones@...aro.org> for STMicroelectronics
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public Licence
> + * as published by the Free Software Foundation; either version
> + * 2 of the Licence, or (at your option) any later version.

MODULE_LICENSE says GPL v2 explicitly. No idea if that is relevant, though.

> + */
> +
> +#include <linux/clk.h>
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/mfd/syscon.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/watchdog.h>
> +
> +/* Low Power Alarm */
> +#define LPC_LPA_LSB_OFF			0x410
> +#define LPC_LPA_START_OFF		0x418
> +
> +/* LPC as WDT */
> +#define LPC_WDT_OFF			0x510
> +
> +#define WATCHDOG_MIN			1
> +#define WATCHDOG_MAX32			4294967 /* 32bit resolution */

Nitpick, but the '32' is really unnecessary here since you don't
have a separate define for a different resolution.

> +
> +#define WDT_ENABLE			1
> +#define WDT_DISABLE			0
> +
> +struct st_wdog_syscfg {
> +	struct regmap *regmap;
> +	unsigned int type_reg;
> +	unsigned int type_mask;
> +	unsigned int enable_reg;
> +	unsigned int enable_mask;

Wondering ... why do you have regmap, type_reg, and enable_reg here
and not in the st_wdog structure ?

Logically all values in this structure could (should) be const,
and it doesn't really make sense to allocate static memory for it.
I can see the argument of having 'nice' looking code and retrieve,
say, enable_reg and enable_mask from the same structure, but that
doesn't really make much sense from a practical perspective. 
If you want that you could as well copy type_mask and enable_mask
into st_wdog.

> +};
> +
> +struct st_wdog {
> +	void __iomem *base;
> +	struct st_wdog_syscfg *syscfg;
> +	struct clk *clk;
> +	int warm_reset;

unsigned int ? Also see below.

> +};
> +
> +static struct st_wdog_syscfg stid127_syscfg = {
> +	.type_mask	= BIT(2),
> +	.enable_mask	= BIT(2),
> +};
> +
> +static struct st_wdog_syscfg stih415_syscfg = {
> +	.type_mask	= BIT(6),
> +	.enable_mask	= BIT(7),
> +};
> +
> +static struct st_wdog_syscfg stih416_syscfg = {
> +	.type_mask	= BIT(6),
> +	.enable_mask	= BIT(7),
> +};
> +
> +static struct st_wdog_syscfg stih407_syscfg = {
> +	.enable_mask	= BIT(19),
> +};
> +
> +static struct of_device_id st_wdog_match[] = {
> +	{
> +		.compatible = "st,stih407-watchdog",
> +		.data = (void *)&stih407_syscfg,
> +	},
> +	{
> +		.compatible = "st,stih416-watchdog",
> +		.data = (void *)&stih416_syscfg,
> +	},
> +	{
> +		.compatible = "st,stih415-watchdog",
> +		.data = (void *)&stih415_syscfg,
> +	},
> +	{
> +		.compatible = "st,stid127-watchdog",
> +		.data = (void *)&stid127_syscfg,
> +	},
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, st_wdog_match);
> +
> +static void st_wdog_setup(struct st_wdog *st_wdog, bool enable)
> +{
> +	/* Type of watchdog reset - 0: Cold 1: Warm */
> +	if (st_wdog->syscfg->type_reg)
> +		regmap_update_bits(st_wdog->syscfg->regmap,
> +				   st_wdog->syscfg->type_reg,
> +				   st_wdog->syscfg->type_mask,
> +				   st_wdog->warm_reset);
> +
> +	/* Mask/unmask watchdog reset */
> +	regmap_update_bits(st_wdog->syscfg->regmap,
> +			   st_wdog->syscfg->enable_reg,
> +			   st_wdog->syscfg->enable_mask,
> +			   !enable);

enable is a bool, but is supposed to provide the value to be put into the
register, masked with enable_mask. Unless I am missing something, the value
is not shifted in regmap_update_bits. So I don't think this can work, but
effectively always writes zero into the mask unless the mask happens to be
at bit position 0 - which never happens.

Same is true for warm_reset above, which also has values 0 or 1.

I know it does not really matter in C (at least when it comes to handling
0 and 1), but I would suggest to avoid mixing booleans with bit masks.

> +}
> +
> +static void st_wdog_load_timer(struct st_wdog *st_wdog, unsigned int timeout)
> +{
> +	timeout *= clk_get_rate(st_wdog->clk);
> +
> +	/* Write only LSB as timeout in Watchdog framework is 32bits only */

I don't entirely understand the logic here. timeout may be 32 bit,
but that doesn't mean that timeout * clk_get_rate(st_wdog->clk)
has to be 32 bit.

Also, what happens if MSB happens to be set to a nonzero value ?
Is that guaranteed to never happen ?

> +	writel_relaxed(timeout, st_wdog->base + LPC_LPA_LSB_OFF);
> +	writel_relaxed(1, st_wdog->base + LPC_LPA_START_OFF);
> +}
> +
> +static int st_wdog_start(struct watchdog_device *wdd)
> +{
> +	struct st_wdog *st_wdog = watchdog_get_drvdata(wdd);
> +
> +	writel_relaxed(1, st_wdog->base + LPC_WDT_OFF);
> +
> +	return 0;
> +}
> +
> +static int st_wdog_stop(struct watchdog_device *wdd)
> +{
> +	struct st_wdog *st_wdog = watchdog_get_drvdata(wdd);
> +
> +	writel_relaxed(0, st_wdog->base + LPC_WDT_OFF);
> +
> +	return 0;
> +}
> +
> +static int st_wdog_set_timeout(struct watchdog_device *wdd,
> +			       unsigned int timeout)
> +{
> +	struct st_wdog *st_wdog = watchdog_get_drvdata(wdd);
> +
> +	wdd->timeout = timeout;
> +	st_wdog_load_timer(st_wdog, timeout);
> +
> +	return 0;
> +}
> +
> +static int st_wdog_keepalive(struct watchdog_device *wdd)
> +{
> +	struct st_wdog *st_wdog = watchdog_get_drvdata(wdd);
> +
> +	st_wdog_load_timer(st_wdog, wdd->timeout);
> +
> +	return 0;
> +}
> +
> +static const struct watchdog_info st_wdog_info = {
> +	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
> +	.identity = "ST LPC WDT",
> +};
> +
> +static const struct watchdog_ops st_wdog_ops = {
> +	.owner		= THIS_MODULE,
> +	.start		= st_wdog_start,
> +	.stop		= st_wdog_stop,
> +	.ping		= st_wdog_keepalive,
> +	.set_timeout	= st_wdog_set_timeout,
> +};
> +
> +static struct watchdog_device st_wdog_dev = {
> +	.info		= &st_wdog_info,
> +	.ops		= &st_wdog_ops,
> +	.min_timeout	= WATCHDOG_MIN,
> +	.max_timeout	= WATCHDOG_MAX32,
> +};
> +
> +static int st_wdog_probe(struct platform_device *pdev)
> +{
> +	const struct of_device_id *match;
> +	struct device_node *np = pdev->dev.of_node;
> +	struct st_wdog *st_wdog;
> +	struct regmap *regmap;
> +	struct resource *res;
> +	struct clk *clk;
> +	void __iomem *base;
> +	int ret;
> +
> +	st_wdog = devm_kzalloc(&pdev->dev, sizeof(*st_wdog), GFP_KERNEL);
> +	if (!st_wdog)
> +		return -ENOMEM;
> +
> +	match = of_match_device(st_wdog_match, &pdev->dev);
> +	if (!match) {
> +		dev_err(&pdev->dev, "Couldn't match device\n");
> +		return -ENODEV;
> +	}
> +	st_wdog->syscfg	= (struct st_wdog_syscfg *)match->data;
> +
> +	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "base");
> +	base = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(base)) {
> +		dev_err(&pdev->dev, "Failed to ioremap base\n");

devm_ioremap_resource already creates an error message, so this should be
unnecessary.

> +		return PTR_ERR(base);
> +	}
> +
> +	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "syscfg-en");
> +	if (!res) {
> +		dev_err(&pdev->dev, "Failed to get enable register address\n");
> +		return -EINVAL;
> +	}
> +	st_wdog->syscfg->enable_reg = res->start;
> +
> +	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "syscfg-type");
> +	if (res)
> +		st_wdog->syscfg->type_reg = res->start;
> +
> +	regmap = syscon_regmap_lookup_by_phandle(np, "st,syscfg");
> +	if (IS_ERR(regmap)) {
> +		dev_err(&pdev->dev, "No syscfg phandle specified\n");
> +		return PTR_ERR(regmap);
> +	}
> +
> +	clk = of_clk_get_by_name(np, "st_wdog");
> +	if (IS_ERR(clk)) {
> +		dev_err(&pdev->dev, "Unable to request clock\n");
> +		return PTR_ERR(clk);
> +	}
> +	clk_prepare_enable(st_wdog->clk);
> +
> +	st_wdog->base 		= base;
> +	st_wdog->clk		= clk;
> +	st_wdog->warm_reset 	= of_property_read_bool(np, "st,warm_reset");
> +	st_wdog->syscfg->regmap = regmap;
> +
> +	watchdog_set_drvdata(&st_wdog_dev, st_wdog);
> +	watchdog_set_nowayout(&st_wdog_dev, WATCHDOG_NOWAYOUT);
> +
> +	ret = watchdog_register_device(&st_wdog_dev);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Unable to register watchdog\n");
> +		clk_disable_unprepare(clk);
> +		return ret;
> +	}
> +
> +	/* Init Watchdog timeout with value in DT */
> +	ret = watchdog_init_timeout(&st_wdog_dev, 0, &pdev->dev);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Unable to initialise watchdog timeout\n");

No clk_disable_unprepare here ?

> +		return ret;
> +	}
> +
> +	st_wdog_setup(st_wdog, WDT_ENABLE);
> +
> +	dev_info(&pdev->dev, "LPC Watchdog driver registered, reset type is %s",
> +		 st_wdog->warm_reset ? "warm" : "cold");
> +
> +	return ret;
> +}
> +
> +static int st_wdog_remove(struct platform_device *pdev)
> +{
> +	struct st_wdog *st_wdog = watchdog_get_drvdata(&st_wdog_dev);
> +
> +	if (watchdog_active(&st_wdog_dev))
> +		st_wdog_stop(&st_wdog_dev);
> +
> +	st_wdog_setup(st_wdog, WDT_DISABLE);
> +
> +	watchdog_unregister_device(&st_wdog_dev);
> +
No clk_disable_unprepare ?

Maye it is not necessary, but then I wonder why you have it above.

> +	return 0;
> +}
> +
> +#ifdef CONFIG_PM
> +static int st_wdog_suspend(struct device *dev)
> +{
> +	if (watchdog_active(&st_wdog_dev))
> +		st_wdog_stop(&st_wdog_dev);
> +

Is any clock activity necessary here ? Just asking, I don't really have an idea.

> +	return 0;
> +}
> +
> +static int st_wdog_resume(struct device *dev)
> +{
> +	struct st_wdog *st_wdog = watchdog_get_drvdata(&st_wdog_dev);
> +
> +	if (watchdog_active(&st_wdog_dev)) {
> +		st_wdog_load_timer(st_wdog, st_wdog_dev.timeout);
> +		st_wdog_start(&st_wdog_dev);
> +	}
> +
> +	return 0;
> +}
> +#endif
> +
> +static SIMPLE_DEV_PM_OPS(st_wdog_pm_ops,
> +			 st_wdog_suspend,
> +			 st_wdog_resume);
> +
> +static struct platform_driver st_wdog_driver = {
> +	.driver	= {
> +		.name = "st-wdt",
> +		.pm = &st_wdog_pm_ops,
> +		.of_match_table = st_wdog_match,
> +	},
> +	.probe = st_wdog_probe,
> +	.remove = st_wdog_remove,
> +};
> +module_platform_driver(st_wdog_driver);
> +
> +MODULE_AUTHOR("David PARIS <david.paris@...com>");
> +MODULE_DESCRIPTION("ST LPC Watchdog Driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 1.9.1
> 
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