[PATCH v2] watchdog: qcom: Add max timeout check to prevent overflow

[Gopinath Sekar]

Added a check to ensure the requested timeout does not exceed the
hardware's maximum supported value. This prevents register overflow
and ensures watchdog reliability.

So, added a check in qcom_wdt_start() to ensure the requested timeout
does not exceed the hardware-supported maximum value. If the requested
value exceeds the maximum value, then the timeout is clamped
at maximum value.

The timeout is first converted to watchdog ticks and then compared
against QCOM_WDT_MAX_TIMEOUT. This helps prevent misconfiguration
and potential watchdog misbehavior due to overflow.

QCOM_WDT_MAX_TIMEOUT is set to 0xFFFFF, as Qualcomm SoCs typically
use 20 bits to store bark/bite timeout values.

This work builds upon the previous submission:
https://lore.kernel.org/u-boot/20250527124926.128413-1-balaji.selvanathan@oss.qualcomm.com/

Signed-off-by: Gopinath Sekar <gopinath.sekar at oss.qualcomm.com>
---
Changes in v2:
- Made changes to clamp the timeout value at SOC supported max value
  if the requested timeout value is greater than max value.
- Link to v1: https://lore.kernel.org/u-boot/20250624061907.3893511-1-gopinath.sekar@oss.qualcomm.com/
---
 drivers/watchdog/qcom-wdt.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
index adbb5aacdc3..af97b27e311 100644
--- a/drivers/watchdog/qcom-wdt.c
+++ b/drivers/watchdog/qcom-wdt.c
@@ -17,6 +17,9 @@
 
 #include <asm/io.h>
 
+/* Maximum allowed timeout value in Qcom SoCs*/
+#define QCOM_WDT_MAX_TIMEOUT	0xfffff
+
 enum wdt_reg {
 	WDT_RST,
 	WDT_EN,
@@ -55,8 +58,24 @@ static void __iomem *wdt_addr(struct qcom_wdt *wdt, enum wdt_reg reg)
 int qcom_wdt_start(struct udevice *dev, u64 timeout_ms, ulong flags)
 {
 	struct qcom_wdt *wdt = dev_get_priv(dev);
-	ulong bark_timeout_s = ((timeout_ms - 1)  * wdt->clk_rate) / 1000;
-	ulong bite_timeout_s = (timeout_ms * wdt->clk_rate) / 1000;
+	u64 tmp_timeout;
+	u32 bark_timeout_s, bite_timeout_s;
+
+	/* Compute timeout in watchdog ticks */
+	tmp_timeout = (timeout_ms * (u64)wdt->clk_rate) / 1000;
+	if (tmp_timeout > QCOM_WDT_MAX_TIMEOUT) {
+		dev_warn(dev,
+			 "Requested timeout (%llu ms) exceeds maximum allowed value (%llu ms). "
+			 "Using max timeout instead.\n",
+			 timeout_ms,
+			 ((u64)QCOM_WDT_MAX_TIMEOUT * 1000) / wdt->clk_rate);
+		tmp_timeout = (u32)QCOM_WDT_MAX_TIMEOUT;
+		timeout_ms = (tmp_timeout * 1000) / wdt->clk_rate;
+	}
+
+	bite_timeout_s = (u32)tmp_timeout;
+	tmp_timeout = ((timeout_ms - 1) * (u64)wdt->clk_rate) / 1000;
+	bark_timeout_s = (u32)tmp_timeout;
 
 	writel(0, wdt_addr(wdt, WDT_EN));
 	writel(BIT(0), wdt_addr(wdt, WDT_RST));
-- 
2.34.1