Date:	Fri, 26 Feb 2016 06:06:24 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Joshua Henderson <joshua.henderson@...rochip.com>,
	linux-kernel@...r.kernel.org
Cc:	linux-mips@...ux-mips.org, ralf@...ux-mips.org,
	Purna Chandra Mandal <purna.mandal@...rochip.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Wim Van Sebroeck <wim@...ana.be>, devicetree@...r.kernel.org,
	linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v2 2/2] watchdog: pic32-wdt: Add PIC32 watchdog driver

On 02/25/2016 10:27 AM, Joshua Henderson wrote:
> Add support for the watchdog peripheral found on PIC32 class
> devices.
>
> Signed-off-by: Joshua Henderson <joshua.henderson@...rochip.com>
> Signed-off-by: Purna Chandra Mandal <purna.mandal@...rochip.com>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> ---
> Note: Please merge this patch series through the MIPS tree.
>
> Changes since v1:
> 	- Shorten commit description
> 	- Don't default to y in Kconfig
> 	- Alphabetical ordering of includes
> 	- Use BIT() where applicable
> 	- Use consistent function name prefixes
> 	- Inline some single use functions
> 	- Use a return of bool when appropriate
> 	- Replace cpu_relax() with nop and explain why this is needed
> 	- Better error handling, especially to prevent divide by zero
> 	- Remove unecessary pr_info().
> 	- Remove redudant driver spinlock which is already covered by
> 	  watchdog core
> 	- Drop .get_timeleft implementation
> 	- Fix typo in compatibility flag and driver name
> 	- Remove wdt->timeout variable and calculation
> 	- Fix race condition in watchdog driver registration
> ---
>   drivers/watchdog/Kconfig     |   13 +++
>   drivers/watchdog/Makefile    |    1 +
>   drivers/watchdog/pic32-wdt.c |  264 ++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 278 insertions(+)
>   create mode 100644 drivers/watchdog/pic32-wdt.c
>
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index 0f6d851..543fa81 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -1414,6 +1414,19 @@ config MT7621_WDT
>   	help
>   	  Hardware driver for the Mediatek/Ralink MT7621/8 SoC Watchdog Timer.
>
> +config PIC32_WDT
> +	tristate "Microchip PIC32 hardware watchdog"
> +	select WATCHDOG_CORE
> +	depends on MACH_PIC32
> +	help
> +	  Watchdog driver for the built in watchdog hardware in a PIC32.
> +
> +	  Configuration bits must be set appropriately for the watchdog to be
> +	  controlled by this driver.
> +
> +	  To compile this driver as a loadable module, choose M here.
> +	  The module will be called pic32-wdt.
> +
>   # PARISC Architecture
>
>   # POWERPC Architecture
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index f566753..244ed80 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -153,6 +153,7 @@ obj-$(CONFIG_LANTIQ_WDT) += lantiq_wdt.o
>   obj-$(CONFIG_RALINK_WDT) += rt2880_wdt.o
>   obj-$(CONFIG_IMGPDC_WDT) += imgpdc_wdt.o
>   obj-$(CONFIG_MT7621_WDT) += mt7621_wdt.o
> +obj-$(CONFIG_PIC32_WDT) += pic32-wdt.o
>
>   # PARISC Architecture
>
> diff --git a/drivers/watchdog/pic32-wdt.c b/drivers/watchdog/pic32-wdt.c
> new file mode 100644
> index 0000000..caec459
> --- /dev/null
> +++ b/drivers/watchdog/pic32-wdt.c
> @@ -0,0 +1,264 @@
> +/*
> + * PIC32 watchdog driver
> + *
> + * Joshua Henderson <joshua.henderson@...rochip.com>
> + * Copyright (c) 2016, Microchip Technology Inc.
> + *
> + * 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.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/clk.h>
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm.h>
> +#include <linux/watchdog.h>
> +
> +#include <asm/mach-pic32/pic32.h>
> +
> +/* Watchdog Timer Registers */
> +#define WDTCON_REG		0x00
> +
> +/* Watchdog Timer Control Register fields */
> +#define WDTCON_WIN_EN		BIT(0)
> +#define WDTCON_RMCS_MASK	0x0003
> +#define WDTCON_RMCS_SHIFT	0x0006
> +#define WDTCON_RMPS_MASK	0x001F
> +#define WDTCON_RMPS_SHIFT	0x0008
> +#define WDTCON_ON		BIT(15)
> +#define WDTCON_CLR_KEY		0x5743
> +
> +/* Reset Control Register fields for watchdog */
> +#define RESETCON_TIMEOUT_IDLE	BIT(2)
> +#define RESETCON_TIMEOUT_SLEEP	BIT(3)
> +#define RESETCON_WDT_TIMEOUT	BIT(4)
> +
> +struct pic32_wdt {
> +	void __iomem	*regs;
> +	void __iomem	*rst_base;
> +	struct clk	*clk;
> +};
> +
> +static inline bool pic32_wdt_is_win_enabled(struct pic32_wdt *wdt)
> +{
> +	return !!(readl(wdt->regs + WDTCON_REG) & WDTCON_WIN_EN);
> +}
> +
> +static inline u32 pic32_wdt_get_post_scaler(struct pic32_wdt *wdt)
> +{
> +	u32 v = readl(wdt->regs + WDTCON_REG);
> +
> +	return (v >> WDTCON_RMPS_SHIFT) & WDTCON_RMPS_MASK;
> +}
> +
> +static inline u32 pic32_wdt_get_clk_id(struct pic32_wdt *wdt)
> +{
> +	u32 v = readl(wdt->regs + WDTCON_REG);
> +
> +	return (v >> WDTCON_RMCS_SHIFT) & WDTCON_RMCS_MASK;
> +}
> +
> +static int pic32_wdt_bootstatus(struct pic32_wdt *wdt)
> +{
> +	u32 v = readl(wdt->rst_base);
> +
> +	writel(RESETCON_WDT_TIMEOUT, PIC32_CLR(wdt->rst_base));
> +
> +	return v & RESETCON_WDT_TIMEOUT;
> +}
> +
> +static int pic32_wdt_get_timeout_secs(struct pic32_wdt *wdt)
> +{
> +	unsigned long rate;
> +	u32 period, ps, terminal;
> +
> +	rate = clk_get_rate(wdt->clk);
> +	if (!rate)
> +		return 0;
> +
> +	pr_debug("wdt: clk_id %d, clk_rate %lu (prescale)\n",
> +		 pic32_wdt_get_clk_id(wdt), rate);
> +

Please pass 'dev' as argument and use dev_dbg().
Then you can also remove the #define pr_fmt above.

> +	/* default, prescaler of 32 (i.e. div-by-32) is implicit. */
> +	rate >>= 5;

Instead of checking rate for 0 above, it might make more sense
to check if it is 0 here.

> +
> +	/* calculate terminal count from postscaler. */
> +	ps = pic32_wdt_get_post_scaler(wdt);
> +	terminal = BIT(ps);
> +
> +	/* find time taken (in secs) to reach terminal count */
> +	period = terminal / rate;

With ps == 31, and rate == 1, the period would end up being 0x80000000,
or negative. Not that it matters (it is assigned to an unsigned on return),
but for consistency it might be better to return an unsigned int.

> +	pr_debug("wdt: clk_rate %lu (postscale) / terminal %d, timeout %dsec\n",
> +		 rate, terminal, period);
> +
> +	return period;
> +}
> +
> +static void pic32_wdt_keepalive(struct pic32_wdt *wdt)
> +{
> +	/* write key through single half-word */
> +	writew(WDTCON_CLR_KEY, wdt->regs + WDTCON_REG + 2);
> +}
> +
> +static int pic32_wdt_start(struct watchdog_device *wdd)
> +{
> +	struct pic32_wdt *wdt = watchdog_get_drvdata(wdd);
> +
> +	writel(WDTCON_ON, PIC32_SET(wdt->regs + WDTCON_REG));
> +	pic32_wdt_keepalive(wdt);
> +
> +	return 0;
> +}
> +
> +static int pic32_wdt_stop(struct watchdog_device *wdd)
> +{
> +	struct pic32_wdt *wdt = watchdog_get_drvdata(wdd);
> +
> +	writel(WDTCON_ON, PIC32_CLR(wdt->regs + WDTCON_REG));
> +	/*
> +	 * Cannot touch registers in the CPU cycle following clearing the
> +	 * ON bit.
> +	 */
> +	nop();
> +
> +	return 0;
> +}
> +
> +static int pic32_wdt_ping(struct watchdog_device *wdd)
> +{
> +	struct pic32_wdt *wdt = watchdog_get_drvdata(wdd);
> +
> +	pic32_wdt_keepalive(wdt);
> +
> +	return 0;
> +}
> +
> +static const struct watchdog_ops pic32_wdt_fops = {
> +	.owner		= THIS_MODULE,
> +	.start		= pic32_wdt_start,
> +	.stop		= pic32_wdt_stop,
> +	.ping		= pic32_wdt_ping,
> +};
> +
> +static const struct watchdog_info pic32_wdt_ident = {
> +	.options = WDIOF_KEEPALIVEPING |
> +			WDIOF_MAGICCLOSE | WDIOF_CARDRESET,
> +	.identity = "PIC32 Watchdog",
> +};
> +
> +static struct watchdog_device pic32_wdd = {
> +	.info		= &pic32_wdt_ident,
> +	.ops		= &pic32_wdt_fops,
> +};
> +
> +static const struct of_device_id pic32_wdt_dt_ids[] = {
> +	{ .compatible = "microchip,pic32mzda-wdt", },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, pic32_wdt_dt_ids);
> +
> +static int pic32_wdt_drv_probe(struct platform_device *pdev)
> +{
> +	int ret;
> +	struct watchdog_device *wdd = &pic32_wdd;
> +	struct pic32_wdt *wdt;
> +	struct resource *mem;
> +
> +	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
> +	if (IS_ERR(wdt))
> +		return PTR_ERR(wdt);
> +
> +	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	wdt->regs = devm_ioremap_resource(&pdev->dev, mem);
> +	if (IS_ERR(wdt->regs))
> +		return PTR_ERR(wdt->regs);
> +
> +	wdt->rst_base = devm_ioremap(&pdev->dev, PIC32_BASE_RESET, 0x10);
> +	if (IS_ERR(wdt->rst_base))
> +		return PTR_ERR(wdt->rst_base);
> +
> +	wdt->clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(wdt->clk)) {
> +		dev_err(&pdev->dev, "clk not found\n");
> +		return PTR_ERR(wdt->clk);
> +	}
> +
> +	ret = clk_prepare_enable(wdt->clk);
> +	if (ret) {
> +		dev_err(&pdev->dev, "clk enable failed\n");
> +		return ret;
> +	}
> +
> +	if (pic32_wdt_is_win_enabled(wdt)) {
> +		dev_err(&pdev->dev, "windowed-clear mode is not supported.\n");
> +		ret = -EOPNOTSUPP;

-ENODEV, please.

> +		goto out_disable_clk;
> +	}
> +
> +	wdd->timeout = pic32_wdt_get_timeout_secs(wdt);
> +	if (!wdd->timeout) {
> +		dev_err(&pdev->dev,
> +			"failed to read watchdog register timeout\n");
> +		ret = -EINVAL;
> +		goto out_disable_clk;
> +	}
> +
> +	dev_info(&pdev->dev, "timeout %d\n", wdd->timeout);
> +
> +	wdd->bootstatus = pic32_wdt_bootstatus(wdt) ? WDIOF_CARDRESET : 0;
> +
> +	watchdog_set_nowayout(wdd, WATCHDOG_NOWAYOUT);
> +	watchdog_set_drvdata(wdd, wdt);
> +
> +	ret = watchdog_register_device(wdd);
> +	if (ret) {
> +		dev_err(&pdev->dev, "watchdog register failed, err %d\n", ret);
> +		goto out_disable_clk;
> +	}
> +
> +	platform_set_drvdata(pdev, wdd);
> +
> +	return 0;
> +
> +out_disable_clk:
> +	clk_disable_unprepare(wdt->clk);
> +
> +	return ret;
> +}
> +
> +static int pic32_wdt_drv_remove(struct platform_device *pdev)
> +{
> +	struct watchdog_device *wdd = platform_get_drvdata(pdev);
> +	struct pic32_wdt *wdt = watchdog_get_drvdata(wdd);
> +
> +	watchdog_unregister_device(wdd);
> +	clk_disable_unprepare(wdt->clk);
> +
> +	return 0;
> +}
> +
> +static struct platform_driver pic32_wdt_driver = {
> +	.probe		= pic32_wdt_drv_probe,
> +	.remove		= pic32_wdt_drv_remove,
> +	.driver		= {
> +		.name		= "pic32-wdt",
> +		.owner		= THIS_MODULE,
> +		.of_match_table = of_match_ptr(pic32_wdt_dt_ids),
> +	}
> +};
> +
> +module_platform_driver(pic32_wdt_driver);
> +
> +MODULE_AUTHOR("Joshua Henderson <joshua.henderson@...rochip.com>");
> +MODULE_DESCRIPTION("Microchip PIC32 Watchdog Timer");
> +MODULE_LICENSE("GPL");
>

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