OMAP4: DPLL cascading: Removed deadlock during DPLL cascading transition

We need take a console lock due to change uart frequency.
We cannot do it under omap_dvfs_lock because it can lead to
deadlock in situation when some thread has taken the console
lock and trying to scale waiting for the omap_dvfs_lock that has
been taken already by DPLL cascading transition.

Example:
+--------------------------------------------+--------------------------------+
|           thread 1                         |           thread 2             |
+--------------------------------------------+--------------------------------+
| ->omap4_dpll_cascading_blocker_release() { |                                |
| ...                                        |                                |
| mutex_lock(dvfs_lock)                      |                                |
| ... ->                                     |                                |
|                                            | -> ...                         |
|                                            | console_lock()                 |
|                                            | omap_device_scale() {          |
|                                            | ...                            |
|                                            | mutex_lock(dvfs_lock) ->       |
| -> ...                                     |                                |
| console_lock() // deadlock                 |                                |
+--------------------------------------------+--------------------------------+

Change-Id: I90f7c66ef9d490a4552e94adddf2e2eb79c58b99
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>

2 files changed, 19 insertions, 11 deletions

diff --git a/arch/arm/mach-omap2/dpll44xx.c b/arch/arm/mach-omap2/dpll44xx.c
index 4a601e4..c258403 100644
--- a/arch/arm/mach-omap2/dpll44xx.c
+++ b/arch/arm/mach-omap2/dpll44xx.c
@@ -17,6 +17,7 @@
 #include <linux/spinlock.h>
 
 #ifdef CONFIG_OMAP4_DPLL_CASCADING
+#include <linux/console.h>
 #include <linux/slab.h>
 #include <linux/cpufreq.h>
 #include "dvfs.h"
@@ -1490,6 +1491,14 @@ int omap4_dpll_cascading_blocker_hold(struct device *dev)
 	if (!dev)
 		return -EINVAL;
 
+	/*
+	 * We need take a console lock due to change uart frequency.
+	 * We cannot do it under omap_dvfs_lock because it can lead to
+	 * deadlock in situation when some thread has taken the console
+	 * lock and trying to scale waiting for the omap_dvfs_lock that has
+	 * been taken already by dpll_cascading.
+	 */
+	console_lock();
 	mutex_lock(&omap_dvfs_lock);
 
 	if (list_empty(&dpll_cascading_blocker_list))
@@ -1522,6 +1531,7 @@ int omap4_dpll_cascading_blocker_hold(struct device *dev)
 	}
 out:
 	mutex_unlock(&omap_dvfs_lock);
+	console_unlock();
 	return ret;
 }
 EXPORT_SYMBOL(omap4_dpll_cascading_blocker_hold);
@@ -1539,6 +1549,14 @@ int omap4_dpll_cascading_blocker_release(struct device *dev)
 	if (!dev)
 		return -EINVAL;
 
+	/*
+	 * We need take a console lock due to change uart frequency.
+	 * We cannot do it under omap_dvfs_lock because it can lead to
+	 * deadlock in situation when some thread has taken the console
+	 * lock and trying to scale waiting for the omap_dvfs_lock that has
+	 * been taken already by dpll_cascading.
+	 */
+	console_lock();
 	mutex_lock(&omap_dvfs_lock);
 
 	/* bail early if list is empty */
@@ -1574,6 +1592,7 @@ int omap4_dpll_cascading_blocker_release(struct device *dev)
 	}
 out:
 	mutex_unlock(&omap_dvfs_lock);
+	console_unlock();
 	return ret;
 }
 EXPORT_SYMBOL(omap4_dpll_cascading_blocker_release);
diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index c994ace..bfaf5d1 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -1488,14 +1488,6 @@ int omap_uart_recalibrate_baud_cb(struct notifier_block *nb,
 	case CLK_PRE_RATE_CHANGE:
 		for (portid = 0 ; portid < OMAP_MAX_HSUART_PORTS ; portid++) {
 			up = ui[portid];
-			/* If Console, Stop from here, till the Frequencies
-			 * Change.
-			 */
-			if (omap_is_console_port(&up->port)) {
-				while (is_console_locked())
-					usleep_range(100, 300);
-				console_stop(up->port.cons);
-			}
 			/* If the device uses the RTS based controlling,
 			 * Pull Up the signal to stop transaction. As the
 			 * Clocks are not disabled. It even if the data
@@ -1571,9 +1563,6 @@ int omap_uart_recalibrate_baud_cb(struct notifier_block *nb,
 				serial_omap_port_disable(up);
 			}
 
-			if (omap_is_console_port(&up->port))
-				console_start(up->port.cons);
-
 			if (up->rts_mux_driver_control)
 				omap_rts_mux_write(0, up->port.line);
 		}