[PATCH v2] watchdog: imx2: fix hang-up on boot for i.MX21, i.MX27 and i.MX31 SoCs

[Vladimir Zapolskiy]

Power down counter enable/disable bit switch is located in WMCR register,
but watchdog controllers found on legacy i.MX21, i.MX27 and i.MX31 SoCs
don't have this register. As a result of writing data to the non-existing
register on driver probe the SoC hangs up, to fix the problem add more OF
compatible strings and on this basis get information about availability of
the WMCR register.

Fixes: 5fe65ce7ccbb ("watchdog: imx2_wdt: Disable power down counter on boot")
Reviewed-by: Guenter Roeck <linux at roeck-us.net>
Tested-by: Magnus Lilja <lilja.magnus at gmail.com>
Reviewed-by: Fabio Estevam <fabio.estevam at nxp.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Vladimir Zapolskiy <vz at mleia.com>
---
Changes from v1 to v2:
* removed i.MX27 and i.MX31 compatibles from the list, since it is expected
  that their DTB files has a reference to the listed i.MX21 compatible,
  many thanks to Uwe Kleine-König for the hint,
* start the list of compatibles from an i.MX35 specific one, since it is
  agreed that i.MX35 precedes i.MX25, thanks to Uwe Kleine-König for review,
* added a comment describing any potential changes in future over the list
  of watchdog compatible values,
* added all collected tags to the commit message.

Changes from RFC to v1:
* replaced private data struct with a macro as suggested by Guenter,
* updated the comment in the source code to reflect the change,
* rearranged and simplified the logic of detecting WMCR presence,
* pulled the fix out from the series with optional proposed DTS changes.

 drivers/watchdog/imx2_wdt.c | 41 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 5 deletions(-)

diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
index 4874b0f..e08c367 100644
--- a/drivers/watchdog/imx2_wdt.c
+++ b/drivers/watchdog/imx2_wdt.c
@@ -30,6 +30,7 @@
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/of_address.h>
+#include <linux/of_device.h>
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
 #include <linux/watchdog.h>
@@ -57,6 +58,7 @@
 #define IMX2_WDT_WICR_WICT	0xFF		/* -> Interrupt Count Timeout */
 
 #define IMX2_WDT_WMCR		0x08		/* Misc Register */
+#define IMX2_WDT_NO_WMCR	((void *)true)	/* Indicates unavailable WMCR */
 
 #define IMX2_WDT_MAX_TIME	128
 #define IMX2_WDT_DEFAULT_TIME	60		/* in seconds */
@@ -70,6 +72,8 @@ struct imx2_wdt_device {
 	bool ext_reset;
 };
 
+static const struct of_device_id imx2_wdt_dt_ids[];
+
 static bool nowayout = WATCHDOG_NOWAYOUT;
 module_param(nowayout, bool, 0);
 MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default="
@@ -242,6 +246,7 @@ static const struct regmap_config imx2_wdt_regmap_config = {
 
 static int __init imx2_wdt_probe(struct platform_device *pdev)
 {
+	const struct of_device_id *of_id;
 	struct imx2_wdt_device *wdev;
 	struct watchdog_device *wdog;
 	struct resource *res;
@@ -310,11 +315,13 @@ static int __init imx2_wdt_probe(struct platform_device *pdev)
 	}
 
 	/*
-	 * Disable the watchdog power down counter at boot. Otherwise the power
-	 * down counter will pull down the #WDOG interrupt line for one clock
-	 * cycle.
+	 * If watchdog controller has WMCR, disable the watchdog power
+	 * down counter at boot. Otherwise the power down counter will
+	 * pull down the #WDOG interrupt line for one clock cycle.
 	 */
-	regmap_write(wdev->regmap, IMX2_WDT_WMCR, 0);
+	of_id = of_match_device(imx2_wdt_dt_ids, &pdev->dev);
+	if (of_id && !of_id->data)
+		regmap_write(wdev->regmap, IMX2_WDT_WMCR, 0);
 
 	ret = watchdog_register_device(wdog);
 	if (ret) {
@@ -411,8 +418,32 @@ static int imx2_wdt_resume(struct device *dev)
 static SIMPLE_DEV_PM_OPS(imx2_wdt_pm_ops, imx2_wdt_suspend,
 			 imx2_wdt_resume);
 
+/*
+ * The list of compatibles is added to achieve compatibility between
+ * old DTS and new kernel while fixing the incompatibility between
+ * i.MX21/i.MX27/i.MX31 and i.MX35/i.MX25/etc. watchdog controllers.
+ *
+ * Please do *NOT* extend the list by adding a compatible value for
+ * a controller, which is compatible with one of the already listed,
+ * almost certainly "fsl,imx35-wdt" compatible serves newer i.MX SoCs.
+ *
+ * You may consider to shrink the list at your own risk, but this may
+ * break the backward compatibility and users may have to update their
+ * DTB, which is good eventually.
+ */
 static const struct of_device_id imx2_wdt_dt_ids[] = {
-	{ .compatible = "fsl,imx21-wdt", },
+	{ .compatible = "fsl,imx21-wdt", .data = IMX2_WDT_NO_WMCR },
+	{ .compatible = "fsl,imx35-wdt",  },
+	{ .compatible = "fsl,imx25-wdt",  },
+	{ .compatible = "fsl,imx50-wdt",  },
+	{ .compatible = "fsl,imx51-wdt",  },
+	{ .compatible = "fsl,imx53-wdt",  },
+	{ .compatible = "fsl,imx6q-wdt",  },
+	{ .compatible = "fsl,imx6sl-wdt", },
+	{ .compatible = "fsl,imx6sx-wdt", },
+	{ .compatible = "fsl,imx6ul-wdt", },
+	{ .compatible = "fsl,imx7d-wdt",  },
+	{ .compatible = "fsl,vf610-wdt",  },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, imx2_wdt_dt_ids);
-- 
2.10.2