[PATCH] watchdog: rti_wdt: Add 10% safety margin to clock frequency

[Stefan Roese]

On 2/21/22 17:21, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka at siemens.com>
> 
> When running against RC_OSC_32k, the watchdog may suffer from running
> faster than expected, expiring earlier. The Linux kernel adds a 10%
> margin to the timeout calculation by slowing down the read clock rate
> accordingly. Do the same here, also to have comparable preset values
> for both drivers.
> 
> Along this, fix the name of the local var holding to frequency - in Hz,
> not kHz.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka at siemens.com>

Applied to u-boot-watchdog/master

Thanks,
Stefan

> ---
>   drivers/watchdog/rti_wdt.c | 14 +++++++++++---
>   1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> index 253286d349b..8d93f19b984 100644
> --- a/drivers/watchdog/rti_wdt.c
> +++ b/drivers/watchdog/rti_wdt.c
> @@ -41,7 +41,7 @@
> 
>   struct rti_wdt_priv {
>   	phys_addr_t regs;
> -	unsigned int clk_khz;
> +	unsigned int clk_hz;
>   };
> 
>   #ifdef CONFIG_WDT_K3_RTI_LOAD_FW
> @@ -139,7 +139,7 @@ static int rti_wdt_start(struct udevice *dev, u64
> timeout_ms, ulong flags)
>   	if (ret < 0)
>   		return ret;
> 
> -	timer_margin = timeout_ms * priv->clk_khz / 1000;
> +	timer_margin = timeout_ms * priv->clk_hz / 1000;
>   	timer_margin >>= WDT_PRELOAD_SHIFT;
>   	if (timer_margin > WDT_PRELOAD_MAX)
>   		timer_margin = WDT_PRELOAD_MAX;
> @@ -185,7 +185,15 @@ static int rti_wdt_probe(struct udevice *dev)
>   	if (ret)
>   		return ret;
> 
> -	priv->clk_khz = clk_get_rate(&clk);
> +	priv->clk_hz = clk_get_rate(&clk);
> +
> +	/*
> +	 * If watchdog is running at 32k clock, it is not accurate.
> +	 * Adjust frequency down in this case so that it does not expire
> +	 * earlier than expected.
> +	 */
> +	if (priv->clk_hz < 32768)
> +		priv->clk_hz = priv->clk_hz * 9 / 10;
> 
>   	return 0;
>   }

Viele Grüße,
Stefan Roese

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