From: Benjamin Herrenschmidt <benh@kernel.crashing.org>

The powermac has a kernel-based driver for controlling the backlight from
the keyboard that used to call into some fbdev's from interrupt contexts. 
This patch moves it to a workqueue (and additionally makes sure the console
semaphore is taken and held).

I hope I'll replace this by the new backlight framework in a future kernel
version, but for now, this will fix the immediate issues with radeon.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 25-akpm/arch/ppc/platforms/pmac_backlight.c |   80 +++++++++++++++++++++-------
 1 files changed, 62 insertions(+), 18 deletions(-)

diff -puN arch/ppc/platforms/pmac_backlight.c~ppc32-move-powermac-backlight-stuff-to-a-workqueue arch/ppc/platforms/pmac_backlight.c
--- 25/arch/ppc/platforms/pmac_backlight.c~ppc32-move-powermac-backlight-stuff-to-a-workqueue	2005-03-13 13:38:33.000000000 -0800
+++ 25-akpm/arch/ppc/platforms/pmac_backlight.c	2005-03-13 13:38:33.000000000 -0800
@@ -12,6 +12,7 @@
 #include <linux/stddef.h>
 #include <linux/reboot.h>
 #include <linux/nvram.h>
+#include <linux/console.h>
 #include <asm/sections.h>
 #include <asm/ptrace.h>
 #include <asm/io.h>
@@ -25,14 +26,19 @@
 #include <linux/adb.h>
 #include <linux/pmu.h>
 
-static struct backlight_controller *backlighter = NULL;
-static void* backlighter_data = NULL;
-static int backlight_autosave = 0;
+static struct backlight_controller *backlighter;
+static void* backlighter_data;
+static int backlight_autosave;
 static int backlight_level = BACKLIGHT_MAX;
 static int backlight_enabled = 1;
+static int backlight_req_level = -1;
+static int backlight_req_enable = -1;
 
-void __pmac
-register_backlight_controller(struct backlight_controller *ctrler, void *data, char *type)
+static void backlight_callback(void *);
+static DECLARE_WORK(backlight_work, backlight_callback, NULL);
+
+void __pmac register_backlight_controller(struct backlight_controller *ctrler,
+					  void *data, char *type)
 {
 	struct device_node* bk_node;
 	char *prop;
@@ -83,16 +89,18 @@ register_backlight_controller(struct bac
 		backlight_level = req.reply[0] >> 4;
 	}
 #endif
+	acquire_console_sem();
 	if (!backlighter->set_enable(1, backlight_level, data))
 		backlight_enabled = 1;
+	release_console_sem();
 
-	printk(KERN_INFO "Registered \"%s\" backlight controller, level: %d/15\n",
-		type, backlight_level);
+	printk(KERN_INFO "Registered \"%s\" backlight controller,"
+	       "level: %d/15\n", type, backlight_level);
 }
 EXPORT_SYMBOL(register_backlight_controller);
 
-void __pmac
-unregister_backlight_controller(struct backlight_controller *ctrler, void *data)
+void __pmac unregister_backlight_controller(struct backlight_controller
+					    *ctrler, void *data)
 {
 	/* We keep the current backlight level (for now) */
 	if (ctrler == backlighter && data == backlighter_data)
@@ -100,22 +108,32 @@ unregister_backlight_controller(struct b
 }
 EXPORT_SYMBOL(unregister_backlight_controller);
 
-int __pmac
-set_backlight_enable(int enable)
+static int __pmac __set_backlight_enable(int enable)
 {
 	int rc;
 
 	if (!backlighter)
 		return -ENODEV;
-	rc = backlighter->set_enable(enable, backlight_level, backlighter_data);
+	acquire_console_sem();
+	rc = backlighter->set_enable(enable, backlight_level,
+				     backlighter_data);
 	if (!rc)
 		backlight_enabled = enable;
+	release_console_sem();
 	return rc;
 }
+int __pmac set_backlight_enable(int enable)
+{
+	if (!backlighter)
+		return -ENODEV;
+	backlight_req_enable = enable;
+	schedule_work(&backlight_work);
+	return 0;
+}
+
 EXPORT_SYMBOL(set_backlight_enable);
 
-int __pmac
-get_backlight_enable(void)
+int __pmac get_backlight_enable(void)
 {
 	if (!backlighter)
 		return -ENODEV;
@@ -123,8 +141,7 @@ get_backlight_enable(void)
 }
 EXPORT_SYMBOL(get_backlight_enable);
 
-int __pmac
-set_backlight_level(int level)
+static int __pmac __set_backlight_level(int level)
 {
 	int rc = 0;
 
@@ -134,10 +151,12 @@ set_backlight_level(int level)
 		level = BACKLIGHT_OFF;
 	if (level > BACKLIGHT_MAX)
 		level = BACKLIGHT_MAX;
+	acquire_console_sem();
 	if (backlight_enabled)
 		rc = backlighter->set_level(level, backlighter_data);
 	if (!rc)
 		backlight_level = level;
+	release_console_sem();
 	if (!rc && !backlight_autosave) {
 		level <<=1;
 		if (level & 0x10)
@@ -146,13 +165,38 @@ set_backlight_level(int level)
 	}
 	return rc;
 }
+int __pmac set_backlight_level(int level)
+{
+	if (!backlighter)
+		return -ENODEV;
+	backlight_req_level = level;
+	schedule_work(&backlight_work);
+	return 0;
+}
+
 EXPORT_SYMBOL(set_backlight_level);
 
-int __pmac
-get_backlight_level(void)
+int __pmac get_backlight_level(void)
 {
 	if (!backlighter)
 		return -ENODEV;
 	return backlight_level;
 }
 EXPORT_SYMBOL(get_backlight_level);
+
+static void backlight_callback(void *dummy)
+{
+	int level, enable;
+
+	do {
+		level = backlight_req_level;
+		enable = backlight_req_enable;
+		mb();
+
+		if (level >= 0)
+			__set_backlight_level(level);
+		if (enable >= 0)
+			__set_backlight_enable(enable);
+	} while(cmpxchg(&backlight_req_level, level, -1) != level ||
+		cmpxchg(&backlight_req_enable, enable, -1) != enable);
+}
_