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

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

[Jan Kiszka]

From: Jan Kiszka <jan.kiszka@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@siemens.com>
---
 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;
 }
-- 
2.34.1

Re: [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@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@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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