[PATCH v5 1/2] watchdog: imx2_wdt: add external reset support via dt prop

[Tim Harvey]

The IMX6 watchdog supports assertion of a signal (WDOG_B) which
can be pinmux'd to an external pin. This is typically used for boards that
have PMIC's in control of the IMX6 power rails. In fact, failure to use
such an external reset on boards with external PMIC's can result in various
hangs due to the IMX6 not being fully reset [1] as well as the board failing
to reset because its PMIC has not been reset to provide adequate voltage for
the CPU when coming out of reset at 800Mhz.

This uses a new device-tree property 'fsl,ext-reset-output' to indicate the
board has such a reset and to cause the watchdog to be configured to assert
WDOG_B instead of an internal reset both on a watchdog timeout and in
system_restart.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/333689.html

Cc: Fabio Estevam <festevam at gmail.com>
Cc: Lucas Stach <l.stach at pengutronix.de>
Cc: Stefan Roese <sr at denx.de>
Cc: Iain Paton <ipaton0 at gmail.com>
Cc: Sascha Hauer <s.hauer at pengutronix.de>
Cc: Akshay Bhat <akshay.bhat at timesys.com>
Cc: Guenter Roeck <linux at roeck-us.net>
Signed-off-by: Tim Harvey <tharvey at gateworks.com>
Reviewed-by: Lucas Stach <l.stach at pengutronix.de>
Acked-by: Shawn Guo <shawn.guo at linaro.org>
---
v5:
 - rename property to 'fsl,ext-reset-output'
v4:
 - change Property to Properties in documentation
v3:
 - mandate use of 'either' internal or external reset but not both
   simultaneously
v2:
 - rename property to 'ext-reset-output' based on ML feedback
 - simplify setting SRS bit if external-reset
 - update comments and commit msg

Signed-off-by: Tim Harvey <tharvey at gateworks.com>
---
 .../devicetree/bindings/watchdog/fsl-imx-wdt.txt      |  4 +++-
 drivers/watchdog/imx2_wdt.c                           | 19 +++++++++++++++++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt
index 8dab6fd..107280e 100644
--- a/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt
+++ b/Documentation/devicetree/bindings/watchdog/fsl-imx-wdt.txt
@@ -5,10 +5,12 @@ Required properties:
 - reg : Should contain WDT registers location and length
 - interrupts : Should contain WDT interrupt
 
-Optional property:
+Optional properties:
 - big-endian: If present the watchdog device's registers are implemented
   in big endian mode, otherwise in native mode(same with CPU), for more
   detail please see: Documentation/devicetree/bindings/regmap/regmap.txt.
+- fsl,ext-reset-output: If present the watchdog device is configured to
+  assert its external reset (WDOG_B) instead of issuing a software reset.
 
 Examples:
 
diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
index e47966a..cb838be 100644
--- a/drivers/watchdog/imx2_wdt.c
+++ b/drivers/watchdog/imx2_wdt.c
@@ -39,6 +39,8 @@
 
 #define IMX2_WDT_WCR		0x00		/* Control Register */
 #define IMX2_WDT_WCR_WT		(0xFF << 8)	/* -> Watchdog Timeout Field */
+#define IMX2_WDT_WCR_WDA	(1 << 5)	/* -> External Reset WDOG_B */
+#define IMX2_WDT_WCR_SRS	(1 << 4)	/* -> Software Reset Signal */
 #define IMX2_WDT_WCR_WRE	(1 << 3)	/* -> WDOG Reset Enable */
 #define IMX2_WDT_WCR_WDE	(1 << 2)	/* -> Watchdog Enable */
 #define IMX2_WDT_WCR_WDZST	(1 << 0)	/* -> Watchdog timer Suspend */
@@ -62,6 +64,7 @@ struct imx2_wdt_device {
 	struct regmap *regmap;
 	struct timer_list timer;	/* Pings the watchdog when closed */
 	struct watchdog_device wdog;
+	bool ext_reset;
 };
 
 static bool nowayout = WATCHDOG_NOWAYOUT;
@@ -85,6 +88,12 @@ static int imx2_wdt_restart(struct watchdog_device *wdog)
 	struct imx2_wdt_device *wdev = watchdog_get_drvdata(wdog);
 	unsigned int wcr_enable = IMX2_WDT_WCR_WDE;
 
+	/* Use internal reset or external - not both */
+	if (wdev->ext_reset)
+		wcr_enable |= IMX2_WDT_WCR_SRS; /* do not assert int reset */
+	else
+		wcr_enable |= IMX2_WDT_WCR_WDA; /* do not assert ext-reset */
+
 	/* Assert SRS signal */
 	regmap_write(wdev->regmap, IMX2_WDT_WCR, wcr_enable);
 	/*
@@ -114,8 +123,12 @@ static inline void imx2_wdt_setup(struct watchdog_device *wdog)
 	val |= IMX2_WDT_WCR_WDZST;
 	/* Strip the old watchdog Time-Out value */
 	val &= ~IMX2_WDT_WCR_WT;
-	/* Generate reset if WDOG times out */
-	val &= ~IMX2_WDT_WCR_WRE;
+	/* Generate internal chip-level reset if WDOG times out */
+	if (!wdev->ext_reset)
+		val &= ~IMX2_WDT_WCR_WRE;
+	/* Or if external-reset assert WDOG_B reset only on time-out */
+	else
+		val |= IMX2_WDT_WCR_WRE;
 	/* Keep Watchdog Disabled */
 	val &= ~IMX2_WDT_WCR_WDE;
 	/* Set the watchdog's Time-Out value */
@@ -263,6 +276,8 @@ static int __init imx2_wdt_probe(struct platform_device *pdev)
 	regmap_read(wdev->regmap, IMX2_WDT_WRSR, &val);
 	wdog->bootstatus = val & IMX2_WDT_WRSR_TOUT ? WDIOF_CARDRESET : 0;
 
+	wdev->ext_reset = of_property_read_bool(pdev->dev.of_node,
+						"fsl,ext-reset-output");
 	wdog->timeout = clamp_t(unsigned, timeout, 1, IMX2_WDT_MAX_TIME);
 	if (wdog->timeout != timeout)
 		dev_warn(&pdev->dev, "Initial timeout out of range! Clamped from %u to %u\n",
-- 
1.9.1