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

[Guenter Roeck]

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@xxxxxxxxxxxxxxxxxxx>
> ---
>
> 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.

> 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@xxxxxxxxxxxxxxxxxxx/
>
>   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.

>   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.

> +	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.

>   	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 ?

>   	/* 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 ?

> +	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 ?

> +	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)