watchdog: meson: keep running if already active

If the watchdog is already running (e.g.: started by bootloader) then
the kernel driver should keep the watchdog active but the amlogic driver
turns it off.

Let the driver fix the clock rate if already active because we do not
know the previous timebase value. To avoid unintentional resetting we
temporarily set it to its maximum value.

Then keep the enable bit if is was previously active.

Signed-off-by: Philippe Boos <[e-mail]>
Reviewed-by: Jerome Brunet <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

drivers/watchdog/meson_gxbb_wdt.c

···
 	struct device *dev = &pdev->dev;
 	struct meson_gxbb_wdt *data;
 	int ret;
+	u32 ctrl_reg;
 
 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
···
 	watchdog_set_nowayout(&data->wdt_dev, nowayout);
 	watchdog_set_drvdata(&data->wdt_dev, data);
 
-	/* Setup with 1ms timebase */
-	writel(((clk_get_rate(data->clk) / 1000) & GXBB_WDT_CTRL_DIV_MASK) |
-		GXBB_WDT_CTRL_EE_RESET |
-		GXBB_WDT_CTRL_CLK_EN |
-		GXBB_WDT_CTRL_CLKDIV_EN,
-		data->reg_base + GXBB_WDT_CTRL_REG);
+	ctrl_reg = readl(data->reg_base + GXBB_WDT_CTRL_REG) &
+				GXBB_WDT_CTRL_EN;
 
+	if (ctrl_reg) {
+		/* Watchdog is running - keep it running but extend timeout
+		 * to the maximum while setting the timebase
+		 */
+		set_bit(WDOG_HW_RUNNING, &data->wdt_dev.status);
+		meson_gxbb_wdt_set_timeout(&data->wdt_dev,
+				GXBB_WDT_TCNT_SETUP_MASK / 1000);
+	}
+
+	/* Setup with 1ms timebase */
+	ctrl_reg |= ((clk_get_rate(data->clk) / 1000) &
+			GXBB_WDT_CTRL_DIV_MASK) |
+			GXBB_WDT_CTRL_EE_RESET |
+			GXBB_WDT_CTRL_CLK_EN |
+			GXBB_WDT_CTRL_CLKDIV_EN;
+
+	writel(ctrl_reg, data->reg_base + GXBB_WDT_CTRL_REG);
 	meson_gxbb_wdt_set_timeout(&data->wdt_dev, data->wdt_dev.timeout);
 
 	return devm_watchdog_register_device(dev, &data->wdt_dev);