watchdog: armada_37xx: Fix compliance with kernel's driver

The Armada 37xx watchdog driver was recently accepted for mainline
kernel by watchdog subsystem maintainer, but the driver works a little
different than the one in U-Boot. This patch fixes this.

In the previous implementation there was a tiny period of time when the
watchdog was disabled and the system was vulnerables - this was during
pinging, which was done by disabling, setting, and enabling the counter.

Now pinging is done without disabling the watchdog. We use 2 counters:
Counter 1 is the watchdog counter - on expiry, the system is reset.
Counter 0 is used to reset Counter 1 to start counting from the set
timeout again. So Counter 1 is set to be reset on Counter 0 expiry event
event and pinging is done by forcing an immediate expiry event on
Counter 0.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Signed-off-by: Stefan Roese <sr@denx.de>

diff --git a/drivers/watchdog/armada-37xx-wdt.c b/drivers/watchdog/armada-37xx-wdt.c
index 0fa4fda..91cd8a6 100644 (file)
--- a/drivers/watchdog/armada-37xx-wdt.c
+++ b/drivers/watchdog/armada-37xx-wdt.c
@@ -22,42 +22,63 @@ struct a37xx_wdt {
 };
 
 /*
- * We use Counter 1 for watchdog timer, because so does Marvell's Linux by
- * default.
+ * We use Counter 1 as watchdog timer, and Counter 0 for re-triggering Counter 1
  */
 
-#define CNTR_CTRL                      0x10
+#define CNTR_CTRL(id)                  ((id) * 0x10)
 #define CNTR_CTRL_ENABLE               0x0001
 #define CNTR_CTRL_ACTIVE               0x0002
 #define CNTR_CTRL_MODE_MASK            0x000c
 #define CNTR_CTRL_MODE_ONESHOT         0x0000
+#define CNTR_CTRL_MODE_HWSIG           0x000c
+#define CNTR_CTRL_TRIG_SRC_MASK                0x00f0
+#define CNTR_CTRL_TRIG_SRC_PREV_CNTR   0x0050
 #define CNTR_CTRL_PRESCALE_MASK                0xff00
 #define CNTR_CTRL_PRESCALE_MIN         2
 #define CNTR_CTRL_PRESCALE_SHIFT       8
 
-#define CNTR_COUNT_LOW                 0x14
-#define CNTR_COUNT_HIGH                        0x18
+#define CNTR_COUNT_LOW(id)             (CNTR_CTRL(id) + 0x4)
+#define CNTR_COUNT_HIGH(id)            (CNTR_CTRL(id) + 0x8)
 
-static void set_counter_value(struct a37xx_wdt *priv)
+static void set_counter_value(struct a37xx_wdt *priv, int id, u64 val)
 {
-       writel(priv->timeout & 0xffffffff, priv->reg + CNTR_COUNT_LOW);
-       writel(priv->timeout >> 32, priv->reg + CNTR_COUNT_HIGH);
+       writel(val & 0xffffffff, priv->reg + CNTR_COUNT_LOW(id));
+       writel(val >> 32, priv->reg + CNTR_COUNT_HIGH(id));
 }
 
-static void a37xx_wdt_enable(struct a37xx_wdt *priv)
+static void counter_enable(struct a37xx_wdt *priv, int id)
 {
-       u32 reg = readl(priv->reg + CNTR_CTRL);
+       setbits_le32(priv->reg + CNTR_CTRL(id), CNTR_CTRL_ENABLE);
+}
 
-       reg |= CNTR_CTRL_ENABLE;
-       writel(reg, priv->reg + CNTR_CTRL);
+static void counter_disable(struct a37xx_wdt *priv, int id)
+{
+       clrbits_le32(priv->reg + CNTR_CTRL(id), CNTR_CTRL_ENABLE);
 }
 
-static void a37xx_wdt_disable(struct a37xx_wdt *priv)
+static int init_counter(struct a37xx_wdt *priv, int id, u32 mode, u32 trig_src)
 {
-       u32 reg = readl(priv->reg + CNTR_CTRL);
+       u32 reg;
+
+       reg = readl(priv->reg + CNTR_CTRL(id));
+       if (reg & CNTR_CTRL_ACTIVE)
+               return -EBUSY;
+
+       reg &= ~(CNTR_CTRL_MODE_MASK | CNTR_CTRL_PRESCALE_MASK |
+                CNTR_CTRL_TRIG_SRC_MASK);
+
+       /* set mode */
+       reg |= mode;
+
+       /* set prescaler to the min value */
+       reg |= CNTR_CTRL_PRESCALE_MIN << CNTR_CTRL_PRESCALE_SHIFT;
+
+       /* set trigger source */
+       reg |= trig_src;
 
-       reg &= ~CNTR_CTRL_ENABLE;
-       writel(reg, priv->reg + CNTR_CTRL);
+       writel(reg, priv->reg + CNTR_CTRL(id));
+
+       return 0;
 }
 
 static int a37xx_wdt_reset(struct udevice *dev)
@@ -67,9 +88,9 @@ static int a37xx_wdt_reset(struct udevice *dev)
        if (!priv->timeout)
                return -EINVAL;
 
-       a37xx_wdt_disable(priv);
-       set_counter_value(priv);
-       a37xx_wdt_enable(priv);
+       /* counter 1 is retriggered by forcing end count on counter 0 */
+       counter_disable(priv, 0);
+       counter_enable(priv, 0);
 
        return 0;
 }
@@ -78,10 +99,14 @@ static int a37xx_wdt_expire_now(struct udevice *dev, ulong flags)
 {
        struct a37xx_wdt *priv = dev_get_priv(dev);
 
-       a37xx_wdt_disable(priv);
-       priv->timeout = 0;
-       set_counter_value(priv);
-       a37xx_wdt_enable(priv);
+       /* first we set timeout to 0 */
+       counter_disable(priv, 1);
+       set_counter_value(priv, 1, 0);
+       counter_enable(priv, 1);
+
+       /* and then we start counter 1 by forcing end count on counter 0 */
+       counter_disable(priv, 0);
+       counter_enable(priv, 0);
 
        return 0;
 }
@@ -89,26 +114,25 @@ static int a37xx_wdt_expire_now(struct udevice *dev, ulong flags)
 static int a37xx_wdt_start(struct udevice *dev, u64 ms, ulong flags)
 {
        struct a37xx_wdt *priv = dev_get_priv(dev);
-       u32 reg;
-
-       reg = readl(priv->reg + CNTR_CTRL);
-
-       if (reg & CNTR_CTRL_ACTIVE)
-               return -EBUSY;
+       int err;
 
-       /* set mode */
-       reg = (reg & ~CNTR_CTRL_MODE_MASK) | CNTR_CTRL_MODE_ONESHOT;
+       err = init_counter(priv, 0, CNTR_CTRL_MODE_ONESHOT, 0);
+       if (err < 0)
+               return err;
 
-       /* set prescaler to the min value */
-       reg &= ~CNTR_CTRL_PRESCALE_MASK;
-       reg |= CNTR_CTRL_PRESCALE_MIN << CNTR_CTRL_PRESCALE_SHIFT;
+       err = init_counter(priv, 1, CNTR_CTRL_MODE_HWSIG,
+                          CNTR_CTRL_TRIG_SRC_PREV_CNTR);
+       if (err < 0)
+               return err;
 
        priv->timeout = ms * priv->clk_rate / 1000 / CNTR_CTRL_PRESCALE_MIN;
 
-       writel(reg, priv->reg + CNTR_CTRL);
+       set_counter_value(priv, 0, 0);
+       set_counter_value(priv, 1, priv->timeout);
+       counter_enable(priv, 1);
 
-       set_counter_value(priv);
-       a37xx_wdt_enable(priv);
+       /* we have to force end count on counter 0 to start counter 1 */
+       counter_enable(priv, 0);
 
        return 0;
 }
@@ -117,7 +141,9 @@ static int a37xx_wdt_stop(struct udevice *dev)
 {
        struct a37xx_wdt *priv = dev_get_priv(dev);
 
-       a37xx_wdt_disable(priv);
+       counter_disable(priv, 1);
+       counter_disable(priv, 0);
+       writel(0, priv->sel_reg);
 
        return 0;
 }
@@ -139,11 +165,10 @@ static int a37xx_wdt_probe(struct udevice *dev)
 
        priv->clk_rate = (ulong)get_ref_clk() * 1000000;
 
-       a37xx_wdt_disable(priv);
-
        /*
-        * We use timer 1 as watchdog timer (because Marvell's Linux uses that
-        * timer as default), therefore we only set bit TIMER1_IS_WCHDOG_TIMER.
+        * We use counter 1 as watchdog timer, therefore we only set bit
+        * TIMER1_IS_WCHDOG_TIMER. Counter 0 is only used to force re-trigger on
+        * counter 1.
         */
        writel(1 << 1, priv->sel_reg);