diff -Napur -X /home/jbarnes/dontdiff linux-2.6.21-rc4/drivers/char/drm/i915_dma.c linux-2.6.21-rc4-modeset/drivers/char/drm/i915_dma.c
--- linux-2.6.21-rc4/drivers/char/drm/i915_dma.c	2007-03-15 17:20:01.000000000 -0700
+++ linux-2.6.21-rc4-modeset/drivers/char/drm/i915_dma.c	2007-03-16 14:03:34.000000000 -0700
@@ -36,6 +36,43 @@
 		       dev->pci_device == 0x2992 || \
 		       dev->pci_device == 0x29A2)
 
+/**
+ * Sets the backlight level.
+ *
+ * \param level backlight level, from 0 to i830_lvds_get_max_backlight().
+ */
+static void lvds_set_backlight(drm_device_t *dev, unsigned long level)
+{
+	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long blc_pwm_ctl;
+
+	blc_pwm_ctl = I915_READ(BLC_PWM_CTL) & ~BACKLIGHT_DUTY_CYCLE_MASK;
+	I915_WRITE(BLC_PWM_CTL, blc_pwm_ctl |
+		   (level << BACKLIGHT_DUTY_CYCLE_SHIFT));
+}
+
+/**
+ * Returns the maximum level of the backlight duty cycle field.
+ */
+static unsigned long lvds_get_max_backlight(drm_device_t *dev)
+{
+	drm_i915_private_t *dev_priv = dev->dev_private;
+    
+	return ((I915_READ(BLC_PWM_CTL) & BACKLIGHT_MODULATION_FREQ_MASK) >>
+		BACKLIGHT_MODULATION_FREQ_SHIFT) * 2;
+}
+
+static int i915_backlight(DRM_IOCTL_ARGS)
+{
+	DRM_DEVICE;
+	
+	lvds_set_backlight(dev, 2);
+	printk(KERN_ERR "max backlight value: %d\n",
+	       lvds_get_max_backlight(dev));
+	return 0;
+}
+
+
 /* Really want an OS-independent resettable timer.  Would like to have
  * this loop run for (eg) 3 sec, but have the timer reset every time
  * the head pointer changes, so that EBUSY only happens if the ring
@@ -784,6 +821,7 @@ drm_ioctl_desc_t i915_ioctls[] = {
 	[DRM_IOCTL_NR(DRM_I915_SET_VBLANK_PIPE)] = { i915_vblank_pipe_set, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY },
 	[DRM_IOCTL_NR(DRM_I915_GET_VBLANK_PIPE)] = { i915_vblank_pipe_get, DRM_AUTH },
 	[DRM_IOCTL_NR(DRM_I915_VBLANK_SWAP)] = {i915_vblank_swap, DRM_AUTH},
+	[DRM_IOCTL_NR(DRM_I915_BACKLIGHT)] = {i915_backlight, DRM_AUTH},
 };
 
 int i915_max_ioctl = DRM_ARRAY_SIZE(i915_ioctls);
diff -Napur -X /home/jbarnes/dontdiff linux-2.6.21-rc4/drivers/char/drm/i915_drm.h linux-2.6.21-rc4-modeset/drivers/char/drm/i915_drm.h
--- linux-2.6.21-rc4/drivers/char/drm/i915_drm.h	2007-03-15 17:20:01.000000000 -0700
+++ linux-2.6.21-rc4-modeset/drivers/char/drm/i915_drm.h	2007-03-16 13:38:16.000000000 -0700
@@ -142,6 +142,7 @@ typedef struct _drm_i915_sarea {
 #define DRM_I915_SET_VBLANK_PIPE	0x0d
 #define DRM_I915_GET_VBLANK_PIPE	0x0e
 #define DRM_I915_VBLANK_SWAP	0x0f
+#define DRM_I915_BACKLIGHT	0x40
 
 #define DRM_IOCTL_I915_INIT		DRM_IOW( DRM_COMMAND_BASE + DRM_I915_INIT, drm_i915_init_t)
 #define DRM_IOCTL_I915_FLUSH		DRM_IO ( DRM_COMMAND_BASE + DRM_I915_FLUSH)
@@ -159,6 +160,7 @@ typedef struct _drm_i915_sarea {
 #define DRM_IOCTL_I915_SET_VBLANK_PIPE	DRM_IOW( DRM_COMMAND_BASE + DRM_I915_SET_VBLANK_PIPE, drm_i915_vblank_pipe_t)
 #define DRM_IOCTL_I915_GET_VBLANK_PIPE	DRM_IOR( DRM_COMMAND_BASE + DRM_I915_GET_VBLANK_PIPE, drm_i915_vblank_pipe_t)
 #define DRM_IOCTL_I915_VBLANK_SWAP	DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_VBLANK_SWAP, drm_i915_vblank_swap_t)
+#define DRM_IOCTL_I915_BACKLIGHT	DRM_IO(DRM_COMMAND_BASE + DRM_I915_BACKLIGHT)
 
 /* Allow drivers to submit batchbuffers directly to hardware, relying
  * on the security mechanisms provided by hardware.
diff -Napur -X /home/jbarnes/dontdiff linux-2.6.21-rc4/drivers/char/drm/i915_drv.h linux-2.6.21-rc4-modeset/drivers/char/drm/i915_drv.h
--- linux-2.6.21-rc4/drivers/char/drm/i915_drv.h	2007-03-15 17:20:01.000000000 -0700
+++ linux-2.6.21-rc4-modeset/drivers/char/drm/i915_drv.h	2007-03-16 12:36:29.000000000 -0700
@@ -294,4 +294,24 @@ extern int i915_wait_ring(drm_device_t *
 
 #define READ_BREADCRUMB(dev_priv) (((u32 *)(dev_priv->hw_status_page))[5])
 
+#define BLC_PWM_CTL		0x61254
+#define BACKLIGHT_MODULATION_FREQ_SHIFT		(17)
+/**
+ * This is the most significant 15 bits of the number of backlight cycles in a
+ * complete cycle of the modulated backlight control.
+ *
+ * The actual value is this field multiplied by two.
+ */
+#define BACKLIGHT_MODULATION_FREQ_MASK		(0x7fff << 17)
+#define BLM_LEGACY_MODE				(1 << 16)
+/**
+ * This is the number of cycles out of the backlight modulation cycle for which
+ * the backlight is on.
+ *
+ * This field must be no greater than the number of cycles in the complete
+ * backlight modulation cycle.
+ */
+#define BACKLIGHT_DUTY_CYCLE_SHIFT		(0)
+#define BACKLIGHT_DUTY_CYCLE_MASK		(0xffff)
+
 #endif