Date:   Mon, 30 Oct 2017 19:09:38 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Guenter Roeck <linux@...ck-us.net>,
        Eric Long <eric.long@...eadtrum.com>
Cc:     Wim Van Sebroeck <wim@...ana.be>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] watchdog: Add Spreadtrum watchdog driver

Hi,

On 30 October 2017 at 17:32, Guenter Roeck <linux@...ck-us.net> wrote:
> On 10/30/2017 02:18 AM, Baolin Wang wrote:
>>
>> Hi Guenter,
>>
>> (There are some problem with Eric's email, he can not receive this
>> email, so I help to reply his comments following yours. sorry for
>> troubles.)
>>
>>>>>> +#define SPRD_WDT_MAX_TIMEOUT           60
>>>>>
>>>>>
>>>>>
>>>>> Is that really the maximum supported timeout ? Seems a bit low.
>>>>> Shouldn't it be something like (U32_MAX / SPRD_WDT_CNT_STEP) ?
>>>>>
>>>>
>>>> It supports the max value like as U32_MAX/SPRD_WDT_CNT_STEP,
>>>> but it doesn't unnecessary to support so big value, if the system can
>>>> not
>>>> response it in 60s, the watchdog could trigger timeout.
>>>>
>>> It is customary to provide the highest possible value here.
>>> No one is forced to set such high values. You are making a choice for
>>> others here. But, sure, if you insist; not worth arguing about.
>>
>>
>> Eric said 60s is better for us, thanks for your patient explanation.
>>
>>>
>>>>>> +
>>>>>> +#define SPRD_WDT_CNT_HIGH_VALUE                16
>>>>>
>>>>>
>>>>>
>>>>> Maybe name it "SPRD_WDT_CNT_HIGH_SHIFT". It is not really a value,
>>>>> it is a shift.
>>>>>
>>>>
>>>> Yes, you are right, _SHIFT will be better.
>>>>
>>>>>>
>>>>>> +#define SPRD_WDT_LOW_VALUE_MASK                GENMASK(15, 0)
>>>>>> +#define SPRD_WDT_CNT_VALUE_MAX         GENMASK(31, 0)
>>>>>
>>>>>
>>>>>
>>>>> Does this mask serve a useful purpose ?
>>>>>
>>>>
>>>> OK, I will remove it, thanks!
>>>>
>>>>>> +#define SPRD_WDT_LOAD_TIMEOUT          1000
>>>>>> +
>>>>>> +struct sprd_wdt {
>>>>>> +       void __iomem *base;
>>>>>> +       struct watchdog_device wdd;
>>>>>> +       struct clk *enable;
>>>>>> +       struct clk *rtc_enable;
>>>>>> +       unsigned int irq;
>>>>>> +};
>>>>>> +
>>>>>> +static inline struct sprd_wdt *to_sprd_wdt(struct watchdog_device
>>>>>> *wdd)
>>>>>> +{
>>>>>> +       return container_of(wdd, struct sprd_wdt, wdd);
>>>>>> +}
>>>>>> +
>>>>>> +static inline void sprd_wdt_lock(void __iomem *addr)
>>>>>> +{
>>>>>> +       writel_relaxed(0x0, addr + SPRD_WDT_LOCK);
>>>>>> +}
>>>>>> +
>>>>>> +static inline void sprd_wdt_unlock(void __iomem *addr)
>>>>>> +{
>>>>>> +       writel_relaxed(SPRD_WDT_UNLOCK_KEY, addr + SPRD_WDT_LOCK);
>>>>>> +}
>>>>>> +
>>>>>> +static inline bool sprd_wdt_is_running(struct sprd_wdt *wdt)
>>>>>> +{
>>>>>> +       u32 val;
>>>>>> +
>>>>>> +       val = readl_relaxed(wdt->base + SPRD_WDT_CTRL);
>>>>>> +       return val & SPRD_WDT_NEW_VER_EN;
>>>>>> +}
>>>>>> +
>>>>>> +static irqreturn_t sprd_wdt_isr(int irq, void *dev_id)
>>>>>> +{
>>>>>> +       struct sprd_wdt *wdt = (struct sprd_wdt *)dev_id;
>>>>>> +
>>>>>> +       sprd_wdt_unlock(wdt->base);
>>>>>> +       writel_relaxed(SPRD_WDT_INT_CLEAR_BIT, wdt->base +
>>>>>> SPRD_WDT_INT_CLR);
>>>>>> +       sprd_wdt_lock(wdt->base);
>>>>>> +       watchdog_notify_pretimeout(&wdt->wdd);
>>>>>> +       return IRQ_HANDLED;
>>>>>> +}
>>>>>> +
>>>>>> +static u32 sprd_wdt_get_cnt_value(struct sprd_wdt *wdt)
>>>>>> +{
>>>>>> +       u32 val;
>>>>>> +
>>>>>> +       val = readl_relaxed(wdt->base + SPRD_WDT_CNT_HIGH) <<
>>>>>> +               SPRD_WDT_CNT_HIGH_VALUE;
>>>>>> +       val |= readl_relaxed(wdt->base + SPRD_WDT_CNT_LOW) &
>>>>>> +               SPRD_WDT_LOW_VALUE_MASK;
>>>>>> +
>>>>>> +       return val;
>>>>>> +}
>>>>>> +
>>>>>> +static int sprd_wdt_load_value(struct sprd_wdt *wdt, u32 timeout,
>>>>>> +                              u32 pretimeout)
>>>>>> +{
>>>>>> +       u32 val, delay_cnt = 0;
>>>>>> +       u32 tmr_step = timeout * SPRD_WDT_CNT_STEP;
>>>>>> +       u32 prtmr_step = pretimeout * SPRD_WDT_CNT_STEP;
>>>>>> +
>>>>>> +       sprd_wdt_unlock(wdt->base);
>>>>>> +       writel_relaxed((tmr_step >> SPRD_WDT_CNT_HIGH_VALUE) &
>>>>>> +                     SPRD_WDT_LOW_VALUE_MASK, wdt->base +
>>>>>> SPRD_WDT_LOAD_HIGH);
>>>>>> +       writel_relaxed((tmr_step & SPRD_WDT_LOW_VALUE_MASK),
>>>>>> +                      wdt->base + SPRD_WDT_LOAD_LOW);
>>>>>> +       writel_relaxed((prtmr_step >> SPRD_WDT_CNT_HIGH_VALUE) &
>>>>>> +                       SPRD_WDT_LOW_VALUE_MASK,
>>>>>> +                      wdt->base + SPRD_WDT_IRQ_LOAD_HIGH);
>>>>>> +       writel_relaxed(prtmr_step & SPRD_WDT_LOW_VALUE_MASK,
>>>>>> +                      wdt->base + SPRD_WDT_IRQ_LOAD_LOW);
>>>>>> +       sprd_wdt_lock(wdt->base);
>>>>>> +
>>>>>> +       /*
>>>>>> +        * Waiting the load value operation done,
>>>>>> +        * it needs two or three RTC clock cycles.
>>>>>> +        */
>>>>>> +       do {
>>>>>> +               val = readl_relaxed(wdt->base + SPRD_WDT_INT_RAW);
>>>>>> +               if (!(val & SPRD_WDT_LD_BUSY_BIT))
>>>>>> +                       break;
>>>>>> +
>>>>>> +               cpu_relax();
>>>>>> +       } while (delay_cnt++ < SPRD_WDT_LOAD_TIMEOUT);
>>>>>> +
>>>>>> +       if (delay_cnt >= SPRD_WDT_LOAD_TIMEOUT)
>>>>>> +               return -EBUSY;
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static int sprd_wdt_enable(struct sprd_wdt *wdt)
>>>>>> +{
>>>>>> +       u32 val;
>>>>>> +       int ret;
>>>>>> +
>>>>>> +       ret = clk_prepare_enable(wdt->enable);
>>>>>> +       if (ret)
>>>>>> +               return ret;
>>>>>> +       ret = clk_prepare_enable(wdt->rtc_enable);
>>>>>> +       if (ret)
>>>>>> +               return ret;
>>>>>> +
>>>>>> +       sprd_wdt_unlock(wdt->base);
>>>>>> +       val = readl_relaxed(wdt->base + SPRD_WDT_CTRL);
>>>>>> +       val |= SPRD_WDT_NEW_VER_EN;
>>>>>> +       writel_relaxed(val, wdt->base + SPRD_WDT_CTRL);
>>>>>> +       sprd_wdt_lock(wdt->base);
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static void sprd_wdt_disable(struct sprd_wdt *wdt)
>>>>>> +{
>>>>>> +       sprd_wdt_unlock(wdt->base);
>>>>>> +       writel_relaxed(0x0, wdt->base + SPRD_WDT_CTRL);
>>>>>> +       sprd_wdt_lock(wdt->base);
>>>>>> +
>>>>>> +       clk_disable_unprepare(wdt->rtc_enable);
>>>>>> +       clk_disable_unprepare(wdt->enable);
>>>>>> +}
>>>>>> +
>>>>>> +static int sprd_wdt_start(struct watchdog_device *wdd)
>>>>>> +{
>>>>>> +       struct sprd_wdt *wdt = to_sprd_wdt(wdd);
>>>>>> +       u32 val;
>>>>>> +       int ret;
>>>>>> +
>>>>>> +       ret = sprd_wdt_load_value(wdt, wdd->timeout, wdd->pretimeout);
>>>>>> +       if (ret)
>>>>>> +               return ret;
>>>>>> +
>>>>>> +       sprd_wdt_unlock(wdt->base);
>>>>>> +       val = readl_relaxed(wdt->base + SPRD_WDT_CTRL);
>>>>>> +       val |= SPRD_WDT_CNT_EN_BIT | SPRD_WDT_INT_EN_BIT |
>>>>>> SPRD_WDT_RST_EN_BIT;
>>>>>> +       writel_relaxed(val, wdt->base + SPRD_WDT_CTRL);
>>>>>> +       sprd_wdt_lock(wdt->base);
>>>>>> +       set_bit(WDOG_HW_RUNNING, &wdd->status);
>>>>>> +
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static int sprd_wdt_stop(struct watchdog_device *wdd)
>>>>>> +{
>>>>>> +       struct sprd_wdt *wdt = to_sprd_wdt(wdd);
>>>>>> +       u32 val;
>>>>>> +
>>>>>> +       sprd_wdt_unlock(wdt->base);
>>>>>> +       val = readl_relaxed(wdt->base + SPRD_WDT_CTRL);
>>>>>> +       val &= ~(SPRD_WDT_CNT_EN_BIT | SPRD_WDT_RST_EN_BIT |
>>>>>> +               SPRD_WDT_INT_EN_BIT);
>>>>>> +       writel_relaxed(val, wdt->base + SPRD_WDT_CTRL);
>>>>>> +       sprd_wdt_lock(wdt->base);
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static int sprd_wdt_set_timeout(struct watchdog_device *wdd,
>>>>>> +                               u32 timeout)
>>>>>> +{
>>>>>> +       struct sprd_wdt *wdt = to_sprd_wdt(wdd);
>>>>>> +
>>>>>> +       if (timeout == wdd->timeout)
>>>>>> +               return 0;
>>>>>> +
>>>>>> +       wdd->timeout = timeout;
>>>>>> +
>>>>>> +       return sprd_wdt_load_value(wdt, timeout, wdd->pretimeout);
>>>>>> +}
>>>>>> +
>>>>>> +static int sprd_wdt_set_pretimeout(struct watchdog_device *wdd,
>>>>>> +                                  u32 new_pretimeout)
>>>>>> +{
>>>>>> +       struct sprd_wdt *wdt = to_sprd_wdt(wdd);
>>>>>> +
>>>>>> +       if (new_pretimeout == wdd->pretimeout)
>>>>>> +               return 0;
>>>>>
>>>>>
>>>>>
>>>>> This is inconsistent. pretimeout == 0 is accepted until it is set
>>>>> to a non-zero value once, then 0 is no longer accepted. pretimeout==0
>>>>> should reflect "pretimeout disabled". If that is not possible you
>>>>> need to set some non-0 default value in the probe function.
>>>>>
>>>>
>>>> I understand your opinion, I will fix it.
>>>>
>>>>>> +       if (new_pretimeout <= wdd->min_timeout)
>>>>>> +               return -EINVAL;
>>>>>
>>>>>
>>>>>
>>>>> Why is pretimeout == wdd->min_timeout invalid ?
>>>>>
>>>>
>>>> OK, you are right, it should be pretimeout < min_timeout.
>>>>
>>>>>> +
>>>>>> +       wdd->pretimeout = new_pretimeout;
>>>>>> +
>>>>>> +       return sprd_wdt_load_value(wdt, wdd->timeout, new_pretimeout);
>>>>>> +}
>>>>>> +
>>>>>> +static u32 sprd_wdt_get_timeleft(struct watchdog_device *wdd)
>>>>>> +{
>>>>>> +       struct sprd_wdt *wdt = to_sprd_wdt(wdd);
>>>>>> +       u32 val;
>>>>>> +
>>>>>> +       val = sprd_wdt_get_cnt_value(wdt);
>>>>>> +       val = val / SPRD_WDT_CNT_STEP;
>>>>>> +
>>>>>> +       return val;
>>>>>> +}
>>>>>> +
>>>>>> +static const struct watchdog_ops sprd_wdt_ops = {
>>>>>> +       .owner = THIS_MODULE,
>>>>>> +       .start = sprd_wdt_start,
>>>>>> +       .stop = sprd_wdt_stop,
>>>>>> +       .set_timeout = sprd_wdt_set_timeout,
>>>>>> +       .set_pretimeout = sprd_wdt_set_pretimeout,
>>>>>> +       .get_timeleft = sprd_wdt_get_timeleft,
>>>>>
>>>>>
>>>>>
>>>>> Just wondering - no heartbeat function ? Having to load the timer
>>>>> values for each heartbeat is expensive.
>>>>>
>>>>
>>>> Unfortunately, this watchdog has not RELOAD register.
>>>>
>>>>>>
>>>>>> +};
>>>>>> +
>>>>>> +static const struct watchdog_info sprd_wdt_info = {
>>>>>> +       .options = WDIOF_SETTIMEOUT |
>>>>>> +                  WDIOF_PRETIMEOUT |
>>>>>> +                  WDIOF_MAGICCLOSE |
>>>>>> +                  WDIOF_KEEPALIVEPING,
>>>>>> +       .identity = "Spreadtrum Watchdog Timer",
>>>>>> +};
>>>>>> +
>>>>>> +static int sprd_wdt_probe(struct platform_device *pdev)
>>>>>> +{
>>>>>> +       struct resource *wdt_res;
>>>>>> +       struct sprd_wdt *wdt;
>>>>>> +       int ret;
>>>>>> +
>>>>>> +       wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
>>>>>> +       if (!wdt)
>>>>>> +               return -ENOMEM;
>>>>>> +
>>>>>> +       wdt_res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>>>>>> +       if (!wdt_res) {
>>>>>> +               dev_err(&pdev->dev, "failed to memory resource\n");
>>>>>> +               return -ENOMEM;
>>>>>> +       }
>>>>>
>>>>>
>>>>>
>>>>> Unnecessary error check and message. devm_ioremap_resource()
>>>>> returns an error if res is NULL.
>>>>>
>>>>
>>>> OK, I will fix it.
>>>>
>>>>>>
>>>>>> +
>>>>>> +       wdt->base = devm_ioremap_resource(&pdev->dev, wdt_res);
>>>>>> +       if (IS_ERR(wdt->base))
>>>>>
>>>>>
>>>>>
>>>>> Move the error message to here.
>>>>>
>>>>>> +               return PTR_ERR(wdt->base);
>>>>>> +
>>>>>> +       wdt->enable = devm_clk_get(&pdev->dev, "enable");
>>>>>> +       if (IS_ERR(wdt->enable)) {
>>>>>> +               dev_err(&pdev->dev, "can't get the enable clock\n");
>>>>>> +               return PTR_ERR(wdt->enable);
>>>>>> +       }
>>>>>> +
>>>>>> +       wdt->rtc_enable = devm_clk_get(&pdev->dev, "rtc_enable");
>>>>>> +       if (IS_ERR(wdt->rtc_enable)) {
>>>>>> +               dev_err(&pdev->dev, "can't get the rtc enable
>>>>>> clock\n");
>>>>>> +               return PTR_ERR(wdt->rtc_enable);
>>>>>> +       }
>>>>>> +
>>>>>> +       wdt->irq = platform_get_irq(pdev, 0);
>>>>>> +       if (wdt->irq < 0) {
>>>>>> +               dev_err(&pdev->dev, "failed to get IRQ resource\n");
>>>>>> +               return wdt->irq;
>>>>>> +       }
>>>>>> +
>>>>>> +       ret = devm_request_irq(&pdev->dev, wdt->irq, sprd_wdt_isr,
>>>>>> +                              IRQF_NO_SUSPEND, "sprd-wdt", (void
>>>>>> *)wdt);
>>>>>> +       if (ret) {
>>>>>> +               dev_err(&pdev->dev, "failed to register irq\n");
>>>>>> +               return ret;
>>>>>> +       }
>>>>>> +
>>>>>> +       wdt->wdd.info = &sprd_wdt_info;
>>>>>> +       wdt->wdd.ops = &sprd_wdt_ops;
>>>>>> +       wdt->wdd.parent = &pdev->dev;
>>>>>> +       wdt->wdd.min_timeout = SPRD_WDT_MIN_TIMROUT;
>>>>>> +       wdt->wdd.max_timeout = SPRD_WDT_MAX_TIMEOUT;
>>>>>> +
>>>>>
>>>>>
>>>>> You might want to set wdt->wdd.timeout to a default value.
>>>>>
>>>>
>>>> OK, I will set a default timeout value in case of no timeout-sec in
>>>> device-tree.
>>>>
>>>>>>
>>>>>> +       ret = sprd_wdt_enable(wdt);
>>>>>> +       if (ret) {
>>>>>> +               dev_err(&pdev->dev, "failed to enable wdt\n");
>>>>>> +               return ret;
>>>>>> +       }
>>>>>> +
>>>>>
>>>>>
>>>>>
>>>>> This needs a matching sprd_wdt_disable() call in the remove function.
>>>>> Best way to handle this would be to add devm_add_action() here.
>>>>>
>>>>
>>>> If add devm_add_action(), it will be called in the remove function,
>>>> but this is not our expect, if someone remove this module, we want it
>>>> just
>>>> timeout.
>>>>
>>>
>>> But that leaves the watchdog enabled even if it was stopped (no call to
>>> sprd_wdt_disable()).
>>
>>
>> Eric said It can not be stopped since we have set WATCHDOG_NOWAYOUT,
>> which means it will reboot the system when removing the watchdog.
>>
>>> Relying on NOWAYOUT would be a better option here. Again, you are
>>> making a choice for the user.
>>
>>
>> we have set WATCHDOG_NOWAYOUT.
>>
> Yes, I understand, but that is configurable.

Yes, you are right. So I think we need add test_bit(WDOG_NO_WAY_OUT,
&wdd->status) in remove function to decide if we should issue
sprd_wdt_disable().


>>>
>>>
>>>>>> +       watchdog_set_nowayout(&wdt->wdd, WATCHDOG_NOWAYOUT);
>>>>>> +       watchdog_init_timeout(&wdt->wdd, 0, &pdev->dev);
>>>>>> +
>>>>>> +       ret = watchdog_register_device(&wdt->wdd);
>>>>>
>>>>>
>>>>>
>>>>> Unfortunately this doesn't work. It leaves interrupts enabled
>>>>> after the watchdog device is removed in sprd_wdt_remove(),
>>>>> but the driver will be gone. I would suggest to use
>>>>> devm_watchdog_register_device() and reorder calls to request
>>>>> the interrupt after registering the watchdog device. Then you
>>>>> can drop the remove function entirely.
>>>>>
>>>>
>>>> Yes, you are right, I understand your opinion, and it is very important,
>>>> devm_watchdog_register_device() is better. Thanks.
>>>>
>>>>>> +       if (ret) {
>>>>>> +               sprd_wdt_disable(wdt);
>>>>>> +               dev_err(&pdev->dev, "failed to register watchdog\n");
>>>>>> +               return ret;
>>>>>> +       }
>>>>>> +       platform_set_drvdata(pdev, wdt);
>>>>>> +
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static int sprd_wdt_remove(struct platform_device *pdev)
>>>>>> +{
>>>>>> +       struct sprd_wdt *wdt = platform_get_drvdata(pdev);
>>>>>> +
>>>>>> +       watchdog_unregister_device(&wdt->wdd);
>>>>>> +
>>>>>> +       if (sprd_wdt_is_running(wdt))
>>>>>> +               dev_crit(&pdev->dev, "Device removed: Expect
>>>>>> reboot!\n");
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static int __maybe_unused sprd_wdt_pm_suspend(struct device *dev)
>>>>>> +{
>>>>>> +       struct watchdog_device *wdd = dev_get_drvdata(dev);
>>>>>> +       struct sprd_wdt *wdt = dev_get_drvdata(dev);
>>>>>> +
>>>>>> +       if (watchdog_active(wdd)) {
>>>>>> +               sprd_wdt_stop(&wdt->wdd);
>>>>>> +               sprd_wdt_disable(wdt);
>>>>>
>>>>>
>>>>>
>>>>> Are you sure you only want to disable the clocks if the watchdog was
>>>>> active ?
>>>>> That seems to be a bit inconsistent.
>>>>>
>>>>
>>>> This watchdog is in always on power domain, if system suspend, it needs
>>>> to
>>>> disable it, or it will timeout.
>>>>
>>> That is not what I asked. I asked why it isn't
>>>
>>>          if (watchdog_active(wdd))
>>>                  sprd_wdt_stop(&wdt->wdd);
>>>
>>>          sprd_wdt_disable(wdt);
>>>
>>> instead.
>>
>>
>> Yes, Eric will fix this in next version.
>>
>>>
>>>>>> +       }
>>>>>> +
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static int __maybe_unused sprd_wdt_pm_resume(struct device *dev)
>>>>>> +{
>>>>>> +       struct watchdog_device *wdd = dev_get_drvdata(dev);
>>>>>> +       struct sprd_wdt *wdt = dev_get_drvdata(dev);
>>>>>> +       int ret;
>>>>>> +
>>>>>> +       if (watchdog_active(wdd)) {
>>>>>> +               ret = sprd_wdt_enable(wdt);
>>>>>> +               if (ret)
>>>>>> +                       return ret;
>>>>>> +               ret = sprd_wdt_start(&wdt->wdd);
>>>>>> +               if (ret) {
>>>>>> +                       sprd_wdt_disable(wdt);
>>>>>> +                       return ret;
>>>>>> +               }
>>>>>
>>>>>
>>>>>
>>>>> This can leave the system in an inconsistent state. Sometimes the wdt
>>>>> may
>>>>> be
>>>>> disabled, sometimes not.
>>>>>
>>>>
>>>> If watchdog enable failed, it means there is something wrong in this
>>>> system.
>>>>
>>>
>>>
>>> True.
>>>
>>> Guenter
>>
>>
>>
>>
>



-- 
Baolin.wang
Best Regards

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