Date:   Mon, 30 Oct 2017 02:32:38 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Baolin Wang <baolin.wang@...aro.org>
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

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.

Guenter

>>
>>
>>>>> +       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
> 
> 
> 

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