Re: [PATCH v4] watchdog: orion_wdt: use timer1 as a pretimeout

[Chris Packham <Chris.Packham@alliedtelesis.co.nz>]

On Wed, 2019-08-28 at 21:45 -0700, Guenter Roeck wrote:
> On 8/28/19 6:53 PM, Chris Packham wrote:
> > The orion watchdog can either reset the CPU or generate an interrupt.
> > The interrupt would be useful for debugging as it provides panic()
> > output about the watchdog expiry, however if the interrupt is used the
> > watchdog can't reset the CPU in the event of being stuck in a loop with
> > interrupts disabled or if the CPU is prevented from accessing memory
> > (e.g. an unterminated DMA).
> > 
> > The Armada SoCs have spare timers that aren't currently used by the
> > Linux kernel. We can use timer1 to provide a pre-timeout ahead of the
> > watchdog timer and provide the possibility of gathering debug before the
> > reset triggers.
> > 
> > Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
> > ---
> > 
> > This was submitted previously[1], the other patches two from the series have
> > been picked up but this one seems to have fallen through the gaps.
> > 
> 
> I had marked it as "under review" but I don't recall why. Maybe it was because
> it depended on the other patches, but I don't recall, and I didn't keep track
> of those patches either. Sorry for that.
> 

No problem. I think it was related to discussions around the other
patches. I had meant to follow up earlier.

> > Changes in v3:
> > - rebase against linux/master
> > Changes in v2:
> > - apply changes to armada-38x only
> > 
> > [1] - https://lore.kernel.org/linux-watchdog/20190305201924.14853-4-chris.packham@alliedtelesis.co.nz/
> > 
> >   drivers/watchdog/orion_wdt.c | 59 ++++++++++++++++++++++++++++++------
> >   1 file changed, 50 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/watchdog/orion_wdt.c b/drivers/watchdog/orion_wdt.c
> > index cdb0d174c5e2..f2e90bfd7186 100644
> > --- a/drivers/watchdog/orion_wdt.c
> > +++ b/drivers/watchdog/orion_wdt.c
> > @@ -46,6 +46,11 @@
> >   #define WDT_AXP_FIXED_ENABLE_BIT BIT(10)
> >   #define WDT_A370_EXPIRED	BIT(31)
> >   
> > +#define TIMER1_VAL_OFF		0x001c
> > +#define TIMER1_ENABLE_BIT	BIT(2)
> > +#define TIMER1_FIXED_ENABLE_BIT	BIT(12)
> > +#define TIMER1_STATUS_BIT	BIT(8)
> > +
> 
> It would be better to group the bits associated with a single register together.
> The bits above are not associated with TIMER1_VAL_OFF, yet the grouping suggests
> that this may be the case.

Will fix.

> 
> >   static bool nowayout = WATCHDOG_NOWAYOUT;
> >   static int heartbeat = -1;		/* module parameter (seconds) */
> >   
> > @@ -158,6 +163,7 @@ static int armadaxp_wdt_clock_init(struct platform_device *pdev,
> >   				   struct orion_watchdog *dev)
> >   {
> >   	int ret;
> > +	u32 val;
> >   
> >   	dev->clk = of_clk_get_by_name(pdev->dev.of_node, "fixed");
> >   	if (IS_ERR(dev->clk))
> > @@ -169,38 +175,48 @@ static int armadaxp_wdt_clock_init(struct platform_device *pdev,
> >   	}
> >   
> >   	/* Enable the fixed watchdog clock input */
> > -	atomic_io_modify(dev->reg + TIMER_CTRL,
> > -			 WDT_AXP_FIXED_ENABLE_BIT,
> > -			 WDT_AXP_FIXED_ENABLE_BIT);
> > +	val = WDT_AXP_FIXED_ENABLE_BIT | TIMER1_FIXED_ENABLE_BIT;
> 
> This always sets TIMER1_FIXED_ENABLE_BIT, but later the enable bit is set
> only conditionally. I don't know what is correct, but this asks for a comment.

The fixed part is safe to set. It just means that the rate is constant.
I'll add a comment.

> 
> > +	atomic_io_modify(dev->reg + TIMER_CTRL, val, val);
> >   
> >   	dev->clk_rate = clk_get_rate(dev->clk);
> > +
> 
> We can only hope we won't see another patch two days from now where someone
> removes this added line.
> 
> I can understand such changes if they fix a checkpatch issue,
> but otherwise please refrain from whitespace changes.

I think it was to appease checkpatch, the one below certainly was. If
it's not needed for checkpatch I'll drop it in the next version.

> 
> >   	return 0;
> >   }
> >   
> >   static int orion_wdt_ping(struct watchdog_device *wdt_dev)
> >   {
> >   	struct orion_watchdog *dev = watchdog_get_drvdata(wdt_dev);
> > +
> >   	/* Reload watchdog duration */
> >   	writel(dev->clk_rate * wdt_dev->timeout,
> >   	       dev->reg + dev->data->wdt_counter_offset);
> > +	if (dev->wdt.info->options & WDIOF_PRETIMEOUT)
> > +		writel(dev->clk_rate * (wdt_dev->timeout - wdt_dev->pretimeout),
> > +		       dev->reg + TIMER1_VAL_OFF);
> > +
> >   	return 0;
> >   }
> >   
> >   static int armada375_start(struct watchdog_device *wdt_dev)
> >   {
> >   	struct orion_watchdog *dev = watchdog_get_drvdata(wdt_dev);
> > -	u32 reg;
> > +	u32 reg, val;
> >   
> 
> Is the second variable here and below really necessary ?
> 

No I can use reg.

> >   	/* Set watchdog duration */
> >   	writel(dev->clk_rate * wdt_dev->timeout,
> >   	       dev->reg + dev->data->wdt_counter_offset);
> > +	if (dev->wdt.info->options & WDIOF_PRETIMEOUT)
> > +		writel(dev->clk_rate * (wdt_dev->timeout - wdt_dev->pretimeout),
> > +		       dev->reg + TIMER1_VAL_OFF);
> >   
> >   	/* Clear the watchdog expiration bit */
> >   	atomic_io_modify(dev->reg + TIMER_A370_STATUS, WDT_A370_EXPIRED, 0);
> >   
> >   	/* Enable watchdog timer */
> > -	atomic_io_modify(dev->reg + TIMER_CTRL, dev->data->wdt_enable_bit,
> > -						dev->data->wdt_enable_bit);
> > +	val = dev->data->wdt_enable_bit;
> > +	if (dev->wdt.info->options & WDIOF_PRETIMEOUT)
> > +		val |= TIMER1_ENABLE_BIT;
> > +	atomic_io_modify(dev->reg + TIMER_CTRL, val, val);
> >   
> >   	/* Enable reset on watchdog */
> >   	reg = readl(dev->rstout);
> > @@ -277,7 +293,7 @@ static int orion_stop(struct watchdog_device *wdt_dev)
> >   static int armada375_stop(struct watchdog_device *wdt_dev)
> >   {
> >   	struct orion_watchdog *dev = watchdog_get_drvdata(wdt_dev);
> > -	u32 reg;
> > +	u32 reg, mask;
> >   
> >   	/* Disable reset on watchdog */
> >   	atomic_io_modify(dev->rstout_mask, dev->data->rstout_mask_bit,
> > @@ -287,7 +303,10 @@ static int armada375_stop(struct watchdog_device *wdt_dev)
> >   	writel(reg, dev->rstout);
> >   
> >   	/* Disable watchdog timer */
> > -	atomic_io_modify(dev->reg + TIMER_CTRL, dev->data->wdt_enable_bit, 0);
> > +	mask = dev->data->wdt_enable_bit;
> > +	if (wdt_dev->info->options & WDIOF_PRETIMEOUT)
> > +		mask += TIMER1_ENABLE_BIT;
> 
> FWIW, += is a bit unusual for a mask. Is it guaranteed that
> the bit is never already set ? Any special reason for using +=
> instead of |= here, but not above ?
> 

I have no idea why on earth I used +=, slip of the keyboard perhaps, |=
is obviously the correct thing to use.

> > +	atomic_io_modify(dev->reg + TIMER_CTRL, mask, 0);
> >   
> >   	return 0;
> >   }
> > @@ -349,7 +368,7 @@ static unsigned int orion_wdt_get_timeleft(struct watchdog_device *wdt_dev)
> >   	return readl(dev->reg + dev->data->wdt_counter_offset) / dev->clk_rate;
> >   }
> >   
> > -static const struct watchdog_info orion_wdt_info = {
> > +static struct watchdog_info orion_wdt_info = {
> >   	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
> >   	.identity = "Orion Watchdog",
> >   };
> > @@ -368,6 +387,16 @@ static irqreturn_t orion_wdt_irq(int irq, void *devid)
> >   	return IRQ_HANDLED;
> >   }
> >   
> > +static irqreturn_t orion_wdt_pre_irq(int irq, void *devid)
> > +{
> > +	struct orion_watchdog *dev = devid;
> > +
> > +	atomic_io_modify(dev->reg + TIMER_A370_STATUS,
> > +			 TIMER1_STATUS_BIT, 0);
> > +	watchdog_notify_pretimeout(&dev->wdt);
> > +	return IRQ_HANDLED;
> > +}
> > +
> >   /*
> >    * The original devicetree binding for this driver specified only
> >    * one memory resource, so in order to keep DT backwards compatibility
> > @@ -589,6 +618,18 @@ static int orion_wdt_probe(struct platform_device *pdev)
> >   		}
> >   	}
> >   
> > +	irq = platform_get_irq(pdev, 1);
> 
> platform_get_irq() may return -EPROBE_DEFER. Are you sure you want to ignore
> the interrupt (and thus disable the pretimeout) if that is the case ?
> 

In any current system that uses this driver I can't imagine a case
where we would see -EPROBE_DEFER here and not for the index 0 interrupt
above. And even then these are SoC interrupt sources so it's unlikely
that they would be deferred.

I do need to handle the case where the 2nd irq is not provided (which
is what I was going for here). IMHO I think it's better to get on with
things rather than deferring the entire driver probe just because an
optional feature isn't ready for use. But if you want me to handle
-EPROBE_DEFER here I will.

> > +	if (irq > 0) {
> > +		orion_wdt_info.options |= WDIOF_PRETIMEOUT;
> > +		ret = devm_request_irq(&pdev->dev, irq, orion_wdt_pre_irq,
> > +				       0, pdev->name, dev);
> > +		if (ret < 0) {
> > +			dev_err(&pdev->dev, "failed to request IRQ\n");
> > +			goto disable_clk;
> > +		}
> > +	}
> > +
> > +
> >   	watchdog_set_nowayout(&dev->wdt, nowayout);
> >   	ret = watchdog_register_device(&dev->wdt);
> >   	if (ret)
> > 
> 
>