diff --git a/src/i830_display.c b/src/i830_display.c
index d16871d..56efa17 100644
--- a/src/i830_display.c
+++ b/src/i830_display.c
@@ -1033,6 +1033,12 @@ i830_crtc_mode_set(xf86CrtcPtr crtc, DisplayModePtr mode,
 
     if (IS_I9XX(pI830)) {
 	refclk = 96000;
+	/* for test only: enable SSC clock (100MHz) if dual channel */
+	if (is_lvds &&
+	    ((INREG(LVDS) & LVDS_CLKB_POWER_MASK) == LVDS_CLKB_POWER_UP)) {
+	    xf86DrvMsg(pScrn->scrnIndex, X_WARNING, "enable SSC clock for LVDS\n");
+	    refclk = 100000;
+	}
     } else {
 	refclk = 48000;
     }
@@ -1188,6 +1194,14 @@ i830_crtc_mode_set(xf86CrtcPtr crtc, DisplayModePtr mode,
     {
 	CARD32 lvds = INREG(LVDS);
 
+	/* for test only: enable SSC clock (100MHz) if dual channel */
+	if ((lvds & LVDS_CLKB_POWER_MASK) == LVDS_CLKB_POWER_UP) {
+	    xf86DrvMsg(pScrn->scrnIndex, X_WARNING,
+		       "enable SSC clock for LVDS, setting dpll_b\n");
+	    dpll &= ~PLL_REF_INPUT_MASK;
+	    dpll |= PLLB_REF_INPUT_SPREADSPECTRUMIN;
+	}
+
 	if (dpll & DPLL_VCO_ENABLE)
 	{
 	    OUTREG(fp_reg, fp);