Disable display pipes and planes a) before setting X modes and b) before
switching back to console -- some chip revisions are not very fond of
having their configuration changed while active. Failing to do so may
result in a black screen after VT switch in X (e.g. ThinkPad X40)

diff --git a/src/i830_driver.c b/src/i830_driver.c
index beb134d..2c27c82 100644
--- a/src/i830_driver.c
+++ b/src/i830_driver.c
@@ -956,11 +956,66 @@ I830SetupOutputs(ScrnInfoPtr pScrn)
    }
 }
 
+/* disable all pipes and associated outputs to bring the card into a defined state */
 static void
-i830_init_clock_gating(ScrnInfoPtr pScrn)
+i830_disable_pipes(ScrnInfoPtr pScrn)
 {
     I830Ptr pI830 = I830PTR(pScrn);
+    
+    uint32_t temp;
+    int disabled_something=0;
+    
+    temp=INREG(DSPACNTR);
+    if ((temp & DISPLAY_PLANE_ENABLE)!=0) {
+	xf86DrvMsg(pScrn->scrnIndex, X_INFO, "Disabling active display plane A.\n");
+	OUTREG(DSPACNTR, temp & ~DISPLAY_PLANE_ENABLE);
+	/* Flush the plane changes */
+	OUTREG(DSPABASE, INREG(DSPABASE));
+	POSTING_READ(DSPABASE);
+	disabled_something=1;
+    }
+    
+    temp=INREG(DSPBCNTR);
+    if ((temp & DISPLAY_PLANE_ENABLE)!=0) {
+	xf86DrvMsg(pScrn->scrnIndex, X_INFO, "Disabling active display plane B.\n");
+	OUTREG(DSPBCNTR, temp & ~DISPLAY_PLANE_ENABLE);
+	/* Flush the plane changes */
+	OUTREG(DSPBBASE, INREG(DSPBBASE));
+	POSTING_READ(DSPBBASE);
+	disabled_something=1;
+    }
 
+    if (!IS_I9XX(pI830) && disabled_something) {
+        /* Wait for vblank for the disable to take effect */
+        i830WaitForVblank(pScrn);
+    }
+    
+    disabled_something=0;
+
+    temp=INREG(PIPEACONF);
+    if ((temp & PIPEACONF_ENABLE)!=0) {
+	xf86DrvMsg(pScrn->scrnIndex, X_INFO, "Disabling active pipe A.\n");
+	OUTREG(PIPEACONF, temp & ~PIPEACONF_ENABLE);
+	POSTING_READ(PIPEACONF);
+	disabled_something=1;
+    }
+    
+    temp=INREG(PIPEBCONF);
+    if ((temp & PIPEACONF_ENABLE)!=0) {
+	xf86DrvMsg(pScrn->scrnIndex, X_INFO, "Disabling active pipe B.\n");
+	OUTREG(PIPEBCONF, temp & ~PIPEACONF_ENABLE);
+	POSTING_READ(PIPEBCONF);
+	disabled_something=1;
+    }
+
+    if (disabled_something) i830WaitForVblank(pScrn);
+}
+
+static void
+i830_init_clock_gating(ScrnInfoPtr pScrn)
+{
+    I830Ptr pI830 = I830PTR(pScrn);
+    
     /* Disable clock gating reported to work incorrectly according to the specs.
      */
     if (IS_G4X(pI830)) {
@@ -2286,6 +2341,8 @@ RestoreHWState(ScrnInfoPtr pScrn)
    }
    i830WaitForVblank(pScrn);
 
+   i830_disable_pipes(pScrn);
+
    if (IS_MOBILE(pI830) && !IS_I830(pI830))
       OUTREG(LVDS, pI830->saveLVDS);
 
@@ -3655,6 +3712,9 @@ I830EnterVT(int scrnIndex, int flags)
        /* Tell the BIOS that we're in control of mode setting now. */
        i830_init_bios_control(pScrn);
 
+       /* Disable any displays and pipes left active by framebuffer console */
+       i830_disable_pipes(pScrn);
+ 
        i830_init_clock_gating(pScrn);
 
        if (pI830->power_context)