Re: [PATCH v4 5/7] Watchdog: introduce ARM SBSA watchdog driver

[Fu Wei]

Hi Gurnter

On 3 June 2015 at 01:07, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> On 06/02/2015 09:55 AM, Fu Wei wrote:
>>
>> Hi Timur,
>>
>> Thanks , feedback inline
>>
>> On 2 June 2015 at 23:32, Timur Tabi <timur@xxxxxxxxxxxxxx> wrote:
>>>
>>> On 06/01/2015 11:05 PM, fu.wei@xxxxxxxxxx wrote:
>>>
>>>> +/*
>>>> + * help functions for accessing 32bit registers of SBSA Generic
>>>> Watchdog
>>>> + */
>>>> +static void sbsa_gwdt_cf_write(unsigned int reg, u32 val,
>>>> +                              struct watchdog_device *wdd)
>>>> +{
>>>> +       struct sbsa_gwdt *gwdt = to_sbsa_gwdt(wdd);
>>>> +
>>>> +       writel_relaxed(val, gwdt->control_base + reg);
>>>> +}
>>>> +
>>>> +static void sbsa_gwdt_rf_write(unsigned int reg, u32 val,
>>>> +                              struct watchdog_device *wdd)
>>>> +{
>>>> +       struct sbsa_gwdt *gwdt = to_sbsa_gwdt(wdd);
>>>> +
>>>> +       writel_relaxed(val, gwdt->refresh_base + reg);
>>>> +}
>>>> +
>>>> +static u32 sbsa_gwdt_cf_read(unsigned int reg, struct watchdog_device
>>>> *wdd)
>>>> +{
>>>> +       struct sbsa_gwdt *gwdt = to_sbsa_gwdt(wdd);
>>>> +
>>>> +       return readl_relaxed(gwdt->control_base + reg);
>>>> +}
>>>
>>>
>>>
>>> I still think you should get rid of these functions and just call
>>> readl_relaxed() and writel_relaxed() every time, but I won't complain
>>> again
>>> if you keep them.
>>
>>
>> yes, that make sense, and will reduce the size of code, and I think
>> the code's readability will be OK too.
>> will try in my next patch,
>>
>>>
>>>> +static irqreturn_t sbsa_gwdt_interrupt(int irq, void *dev_id)
>>>> +{
>>>> +       struct sbsa_gwdt *gwdt = (struct sbsa_gwdt *)dev_id;
>>>> +       struct watchdog_device *wdd = &gwdt->wdd;
>>>> +
>>>> +       if (wdd->pretimeout)
>>>> +               /* The pretimeout is valid, go panic */
>>>> +               panic("SBSA Watchdog pre-timeout");
>>>> +       else
>>>> +               /* We don't use pretimeout, trigger WS1 now*/
>>>> +               sbsa_gwdt_set_wcv(wdd, 0);
>>>
>>>
>>>
>>> I don't like this.
>>
>>
>> If so, what is your idea ,if pretimeout == 0?
>>
>> the reason of using WCV as (timout - pretimeout): it can provide the
>> longer timeout period,
>> (1)If we use WOR, it can only provide 10s @ 400MHz(max).
>> as Guenter said earlier, the default timer out for most watchdog will
>> be 30s, so I think 10s limit will be a little short
>> (2)we can always program WCV just like ping.
>> (3)if a timeout arrives, WOR will be use, so use it as pretimeout, but
>> we still can make this pretimeout longer by programming WCV(I don't
>> think it's necessary)
>>
>>
>>> The triggering of the hardware reset should never depend
>>> on an interrupt being handled properly.
>>
>>
>> if this fail, system reset in 1S, because WOR == (1s)
>>
> So ?

Even the interrupt routine isn't triggered,  (WOR + system counter) --> WCV,
then, sy system reset in 1S.

the hardware reset doesn't depend on an interrupt.


>
>>> You should always program WCV
>>> correctly in advance.  This is especially true since pre-timeout will
>>> probably rarely be used.
>>
>>
>> always programming WCV is doable.  But I absolutely can not agree "
>> pre-timeout will probably rarely be used"
>> If so, SBSA watchdog is just a normal watchdog,  This use case just
>> makes this HW useless.
>> If so, go to use SP805.
>> you still don't see the importance of this warning and pretimeout to a
>> real server.
>>
>
> If pretimeout isn't used, why not just set WCV = timeout, WOR = 0 ?

Because if WOR = 0 , according to SBSA,  once you want to enable watchdog,
(0 + system counter) --> WCV , then , WS0 and WS1 will be triggered immediately.
we have not a chance(a time slot) to update WCV.

>
> Guenter
>
>
>> If the software of a real server goes wrong, then you just directly
>> restart it ,
>> never try to sync/protect the current data, never try to figure out
>> what is wrong with it.
>> I don't think that is a good server software.
>>
>> At least, I don't thinks " pre-timeout will probably rarely be used"
>> is a good idea for a server.
>> in another word, in a server ,pre-timeout should always be used.
>>
>>> So what happens if the CPU is totally hung and
>>
>>
>> Again, system reset in 1S, because WOR == (1s).
>>
>>> this interrupt handler is never called?  When will the timeout occur?
>>
>>
>> if this interrupt hardler is never called,  what I can see is "some
>> one is feeding the dog".
>> OK, in case, WS0 is triggered, but  this interrupt hardler isn't
>> called, then software really goes wrong.  Then , Again, Again system
>> reset in 1S, because WOR == (1s).
>>
>>>
>>>> +static int sbsa_gwdt_probe(struct platform_device *pdev)
>>>> +{
>>>> +       u64 first_period_max = U64_MAX;
>>>> +       struct device *dev = &pdev->dev;
>>>> +       struct watchdog_device *wdd;
>>>> +       struct sbsa_gwdt *gwdt;
>>>> +       struct resource *res;
>>>> +       void *rf_base, *cf_base;
>>>> +       int ret, irq;
>>>> +       u32 status;
>>>> +
>>>> +       gwdt = devm_kzalloc(dev, sizeof(*gwdt), GFP_KERNEL);
>>>> +       if (!gwdt)
>>>> +               return -ENOMEM;
>>>> +       platform_set_drvdata(pdev, gwdt);
>>>
>>>
>>>
>>> You should probably do this *after* calling platform_get_irq_byname().
>>
>>
>>   it just dose (pdev->) dev->driver_data = gwdt
>> If we got gwdt, we can do that.
>>
>> But maybe I miss something(or a rule of usage),  so please let know
>> why this has to be called  *after* calling platform_get_irq_byname().
>>
>>>
>>>> +
>>>> +       res = platform_get_resource_byname(pdev, IORESOURCE_MEM,
>>>> "refresh");
>>>> +       rf_base = devm_ioremap_resource(dev, res);
>>>> +       if (IS_ERR(rf_base))
>>>> +               return PTR_ERR(rf_base);
>>>> +
>>>> +       res = platform_get_resource_byname(pdev, IORESOURCE_MEM,
>>>> "control");
>>>> +       cf_base = devm_ioremap_resource(dev, res);
>>>> +       if (IS_ERR(cf_base))
>>>> +               return PTR_ERR(cf_base);
>>>> +
>>>> +       irq = platform_get_irq_byname(pdev, "ws0");
>>>> +       if (irq < 0) {
>>>> +               dev_err(dev, "unable to get ws0 interrupt.\n");
>>>> +               return irq;
>>>> +       }
>>>> +
>>>> +       /*
>>>> +        * Get the frequency of system counter from the cp15 interface
>>>> of
>>>> ARM
>>>> +        * Generic timer. We don't need to check it, because if it
>>>> returns
>>>> "0",
>>>> +        * system would panic in very early stage.
>>>> +        */
>>>> +       gwdt->clk = arch_timer_get_cntfrq();
>>>> +       gwdt->refresh_base = rf_base;
>>>> +       gwdt->control_base = cf_base;
>>>> +
>>>> +       wdd = &gwdt->wdd;
>>>> +       wdd->parent = dev;
>>>> +       wdd->info = &sbsa_gwdt_info;
>>>> +       wdd->ops = &sbsa_gwdt_ops;
>>>> +       watchdog_set_drvdata(wdd, gwdt);
>>>> +       watchdog_set_nowayout(wdd, nowayout);
>>>> +
>>>> +       wdd->min_pretimeout = 0;
>>>> +       wdd->max_pretimeout = U32_MAX / gwdt->clk;
>>>> +       wdd->min_timeout = 1;
>>>> +       do_div(first_period_max, gwdt->clk);
>>>> +       wdd->max_timeout = first_period_max;
>>>> +
>>>> +       wdd->pretimeout = DEFAULT_PRETIMEOUT;
>>>> +       wdd->timeout = DEFAULT_TIMEOUT;
>>>> +       watchdog_init_timeouts(wdd, pretimeout, timeout, dev);
>>>> +
>>>> +       status = sbsa_gwdt_cf_read(SBSA_GWDT_WCS, wdd);
>>>> +       if (status & SBSA_GWDT_WCS_WS1) {
>>>> +               dev_warn(dev, "System reset by WDT(WCV: %llx)\n",
>>>> +                        sbsa_gwdt_get_wcv(wdd));
>>>
>>>
>>>
>>> "System was previously reset via watchdog" is much clearer.
>>
>>
>> OK
>>
>>>
>>>> +               wdd->bootstatus |= WDIOF_CARDRESET;
>>>> +       }
>>>> +       /* Check if watchdog is already enabled */
>>>> +       if (status & SBSA_GWDT_WCS_EN) {
>>>> +               dev_warn(dev, "already enabled!\n");
>>>
>>>
>>>
>>> "watchdog is already enabled".
>>
>>
>> I think I don't need to print "watchdog",   dev_warn(dev,  has help us on
>> this.
>> If you do so , the message will be "watchdog: watchdog0: watchdog is
>> already enabled"
>>
>>   > Never use exclamation marks in kernel
>>>
>>> messages.
>>
>>
>> that make sense , will delete it.
>>
>>>
>>>> +               sbsa_gwdt_keepalive(wdd);
>>>> +       }
>>>> +
>>>> +       /* update pretimeout to WOR */
>>>> +       sbsa_gwdt_set_pretimeout(wdd, wdd->pretimeout);
>>>> +
>>>> +       ret = devm_request_irq(dev, irq, sbsa_gwdt_interrupt, 0,
>>>> +                              pdev->name, gwdt);
>>>> +       if (ret) {
>>>> +               dev_err(dev, "unable to request IRQ %d\n", irq);
>>>> +               return ret;
>>>> +       }
>>>> +
>>>> +       ret = watchdog_register_device(wdd);
>>>> +       if (ret)
>>>> +               return ret;
>>>> +
>>>> +       dev_info(dev, "Initialized with %ds timeout, %ds pretimeout @ %u
>>>> Hz\n",
>>>> +                wdd->timeout, wdd->pretimeout, gwdt->clk);
>>>
>>>
>>>
>>> if (wdd->pretimeout)
>>>          "watchdog initialized to %us timeout and %us pre-timeout at %u
>>> Hz\n", wdd->timeout, wdd->pretimeout, gwdt->clk
>>> else
>>>          "watchdog initialized to %us timeout at %u Hz\n", wdd->timeout,
>>> gwdt->clk
>>>
>>> I think it's unlikely that users will use pre-timeout, so your code
>>> should
>>> treat pre-timeout as a special case, not the normal usage.
>>
>>
>> I don't think so, that why you didn't use pretimeout in your driver.
>> Because you don't see the meaning of "pretimeout" to a  server.
>>
>>>
>>> --
>>> Qualcomm Innovation Center, Inc.
>>> The Qualcomm Innovation Center, Inc. is a member of the
>>> Code Aurora Forum, a Linux Foundation Collaborative Project.
>>
>>
>>
>>
>



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat Software (Beijing) Co.,Ltd.Shanghai Branch
Ph: +86 21 61221326(direct)
Ph: +86 186 2020 4684 (mobile)
Room 1512, Regus One Corporate Avenue,Level 15,
One Corporate Avenue,222 Hubin Road,Huangpu District,
Shanghai,China 200021
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