Re: [PATCHv2 3/4] watchdog: Add K3 RTI watchdog support

[Guenter Roeck <linux@roeck-us.net>]

On 3/3/20 10:57 PM, Tero Kristo wrote:
> On 03/03/2020 23:18, Guenter Roeck wrote:
>> On Mon, Mar 02, 2020 at 10:04:25PM +0200, Tero Kristo wrote:
>>> Texas Instruments K3 SoCs contain an RTI (Real Time Interrupt) module
>>> which can be used as a watchdog. This IP provides a support for
>>> windowed watchdog mode, in which the watchdog must be petted within
>>> a certain time window. If it is petted either too soon, or too late,
>>> a watchdog error will be triggered.
>>>
>>> Signed-off-by: Tero Kristo <t-kristo@ti.com>
>>> ---
>>> v2:
>>>    * Added better documentation within the driver code
>>>    * Dropped fck handle, instead get the fck rate during probe only
>>>    * Modified the max_hw_heartbeat calculation logic a bit
>>>
>>>   drivers/watchdog/Kconfig   |   8 ++
>>>   drivers/watchdog/Makefile  |   1 +
>>>   drivers/watchdog/rti_wdt.c | 254 +++++++++++++++++++++++++++++++++++++
>>>   3 files changed, 261 insertions(+)
>>>   create mode 100644 drivers/watchdog/rti_wdt.c
>>>
>>> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
>>> index cec868f8db3f..81faf47d44a6 100644
>>> --- a/drivers/watchdog/Kconfig
>>> +++ b/drivers/watchdog/Kconfig
>>> @@ -583,6 +583,14 @@ config DAVINCI_WATCHDOG
>>>         NOTE: once enabled, this timer cannot be disabled.
>>>         Say N if you are unsure.
>>>   +config K3_RTI_WATCHDOG
>>> +    tristate "Texas Instruments K3 RTI watchdog"
>>> +    depends on ARCH_K3 || COMPILE_TEST
>>> +    select WATCHDOG_CORE
>>> +    help
>>> +      Say Y here if you want to include support for the K3 watchdog
>>> +      timer (RTI module) available in the K3 generation of processors.
>>> +
>>>   config ORION_WATCHDOG
>>>       tristate "Orion watchdog"
>>>       depends on ARCH_ORION5X || ARCH_DOVE || MACH_DOVE || ARCH_MVEBU || (COMPILE_TEST && !ARCH_EBSA110)
>>> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
>>> index 2ee352bf3372..6de2e4ceef19 100644
>>> --- a/drivers/watchdog/Makefile
>>> +++ b/drivers/watchdog/Makefile
>>> @@ -57,6 +57,7 @@ obj-$(CONFIG_EP93XX_WATCHDOG) += ep93xx_wdt.o
>>>   obj-$(CONFIG_PNX4008_WATCHDOG) += pnx4008_wdt.o
>>>   obj-$(CONFIG_IOP_WATCHDOG) += iop_wdt.o
>>>   obj-$(CONFIG_DAVINCI_WATCHDOG) += davinci_wdt.o
>>> +obj-$(CONFIG_K3_RTI_WATCHDOG) += rti_wdt.o
>>>   obj-$(CONFIG_ORION_WATCHDOG) += orion_wdt.o
>>>   obj-$(CONFIG_SUNXI_WATCHDOG) += sunxi_wdt.o
>>>   obj-$(CONFIG_RN5T618_WATCHDOG) += rn5t618_wdt.o
>>> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
>>> new file mode 100644
>>> index 000000000000..7a46c40891e2
>>> --- /dev/null
>>> +++ b/drivers/watchdog/rti_wdt.c
>>> @@ -0,0 +1,254 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * Watchdog driver for the K3 RTI module
>>> + *
>>> + * (c) Copyright 2019-2020 Texas Instruments Inc.
>>> + * All rights reserved.
>>> + */
>>> +
>>> +#include <linux/clk.h>
>>> +#include <linux/device.h>
>>> +#include <linux/err.h>
>>> +#include <linux/io.h>
>>> +#include <linux/kernel.h>
>>> +#include <linux/mod_devicetable.h>
>>> +#include <linux/module.h>
>>> +#include <linux/moduleparam.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/pm_runtime.h>
>>> +#include <linux/types.h>
>>> +#include <linux/watchdog.h>
>>> +
>>> +#define DEFAULT_HEARTBEAT 60
>>> +
>>> +/* Max heartbeat is calculated at 32kHz source clock */
>>> +#define MAX_HEARTBEAT    1000
>>> +
>>> +/* Timer register set definition */
>>> +#define RTIDWDCTRL    0x90
>>> +#define RTIDWDPRLD    0x94
>>> +#define RTIWDSTATUS    0x98
>>> +#define RTIWDKEY    0x9c
>>> +#define RTIDWDCNTR    0xa0
>>> +#define RTIWWDRXCTRL    0xa4
>>> +#define RTIWWDSIZECTRL    0xa8
>>> +
>>> +#define RTIWWDRX_NMI    0xa
>>> +
>>> +#define RTIWWDSIZE_50P    0x50
>>> +
>>> +#define WDENABLE_KEY    0xa98559da
>>> +
>>> +#define WDKEY_SEQ0        0xe51a
>>> +#define WDKEY_SEQ1        0xa35c
>>> +
>>> +#define WDT_PRELOAD_SHIFT    13
>>> +
>>> +#define WDT_PRELOAD_MAX        0xfff
>>> +
>>> +#define DWDST            BIT(1)
>>> +
>>> +static int heartbeat;
>>> +
>>> +/*
>>> + * struct to hold data for each WDT device
>>> + * @base - base io address of WD device
>>> + * @freq - source clock frequency of WDT
>>> + * @wdd  - hold watchdog device as is in WDT core
>>> + */
>>> +struct rti_wdt_device {
>>> +    void __iomem        *base;
>>> +    unsigned long        freq;
>>> +    struct watchdog_device    wdd;
>>> +};
>>> +
>>> +static int rti_wdt_start(struct watchdog_device *wdd)
>>> +{
>>> +    u32 timer_margin;
>>> +    struct rti_wdt_device *wdt = watchdog_get_drvdata(wdd);
>>> +
>>> +    /* set timeout period */
>>> +    timer_margin = (u64)wdd->timeout * wdt->freq;
>>> +    timer_margin >>= WDT_PRELOAD_SHIFT;
>>> +    if (timer_margin > WDT_PRELOAD_MAX)
>>> +        timer_margin = WDT_PRELOAD_MAX;
>>> +    writel_relaxed(timer_margin, wdt->base + RTIDWDPRLD);
>>> +
>>> +    /*
>>> +     * RTI only supports a windowed mode, where the watchdog can only
>>> +     * be petted during the open window; not too early or not too late.
>>> +     * The HW configuration options only allow for the open window size
>>> +     * to be 50% or less than that; we obviouly want to configure the open
>>> +     * window as large as possible so we select the 50% option. To avoid
>>> +     * any glitches, we accommodate 5% safety margin also, so we setup
>>> +     * the min_hw_hearbeat at 55% of the timeout period.
>>> +     */
>>> +    wdd->min_hw_heartbeat_ms = 11 * wdd->timeout * 1000 / 20;
>>> +
>>> +    /* Generate NMI when wdt expires */
>>> +    writel_relaxed(RTIWWDRX_NMI, wdt->base + RTIWWDRXCTRL);
>>> +
>>> +    /* Open window size 50%; this is the largest window size available */
>>> +    writel_relaxed(RTIWWDSIZE_50P, wdt->base + RTIWWDSIZECTRL);
>>> +
>>> +    readl_relaxed(wdt->base + RTIWWDSIZECTRL);
>>> +
>>> +    /* enable watchdog */
>>> +    writel_relaxed(WDENABLE_KEY, wdt->base + RTIDWDCTRL);
>>> +    return 0;
>>> +}
>>> +
>>> +static int rti_wdt_ping(struct watchdog_device *wdd)
>>> +{
>>> +    struct rti_wdt_device *wdt = watchdog_get_drvdata(wdd);
>>> +
>>> +    /* put watchdog in service state */
>>> +    writel_relaxed(WDKEY_SEQ0, wdt->base + RTIWDKEY);
>>> +    /* put watchdog in active state */
>>> +    writel_relaxed(WDKEY_SEQ1, wdt->base + RTIWDKEY);
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static unsigned int rti_wdt_get_timeleft(struct watchdog_device *wdd)
>>> +{
>>> +    u64 timer_counter;
>>> +    u32 val;
>>> +    struct rti_wdt_device *wdt = watchdog_get_drvdata(wdd);
>>> +
>>> +    /* if timeout has occurred then return 0 */
>>> +    val = readl_relaxed(wdt->base + RTIWDSTATUS);
>>> +    if (val & DWDST)
>>> +        return 0;
>>> +
>>> +    timer_counter = readl_relaxed(wdt->base + RTIDWDCNTR);
>>> +
>>> +    do_div(timer_counter, wdt->freq);
>>> +
>>> +    return timer_counter;
>>> +}
>>> +
>>> +static const struct watchdog_info rti_wdt_info = {
>>> +    .options = WDIOF_KEEPALIVEPING,
>>> +    .identity = "K3 RTI Watchdog",
>>> +};
>>> +
>>> +static const struct watchdog_ops rti_wdt_ops = {
>>> +    .owner        = THIS_MODULE,
>>> +    .start        = rti_wdt_start,
>>> +    .ping        = rti_wdt_ping,
>>> +    .get_timeleft    = rti_wdt_get_timeleft,
>>> +};
>>> +
>>> +static int rti_wdt_probe(struct platform_device *pdev)
>>> +{
>>> +    int ret = 0;
>>> +    struct device *dev = &pdev->dev;
>>> +    struct resource *wdt_mem;
>>> +    struct watchdog_device *wdd;
>>> +    struct rti_wdt_device *wdt;
>>> +    struct clk *clk;
>>> +
>>> +    wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
>>> +    if (!wdt)
>>> +        return -ENOMEM;
>>> +
>>> +    clk = devm_clk_get(dev, NULL);
>>> +    if (IS_ERR(clk)) {
>>> +        if (PTR_ERR(clk) != -EPROBE_DEFER)
>>> +            dev_err(dev, "failed to get clock\n");
>>> +        return PTR_ERR(clk);
>>> +    }
>>> +
>>> +    wdt->freq = clk_get_rate(clk);
>>> +    if (!wdt->freq) {
>>> +        dev_err(dev, "Failed to get fck rate.\n");
>>> +        return -EINVAL;
>>> +    }
>>> +
>>> +    devm_clk_put(dev, clk);
>>> +
>> Are you sure about this ? Doesn't this mean that the clock may be stopped ?
>> Normally the reason for using devm_ functions during probe is that release
>> functions are called automatically when the device is removed. Calling
>> the release function dorectly is unusual and most of the time wrong.
> 
> clk_get / clk_put does not enable / disable a clock by itself, this is just used to fetch a clock handle. But you are right, we are never calling clk_enable on it either, because at least the 32kHz clock we are interested in is of type always-on and can never be disabled.
> 
> I can keep the clock handle and call enable/disable on it in the probe/remove if you think that would be neater.
> 

If it isn't needed to be held, you should use clk_get / clk_put,
and not the devm_ functions.

Guenter