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

[Guenter Roeck]

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 ?

> > 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 ?

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.

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