drm/i915: Use the real FDI frequency for determining b/w

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 16 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index df410e4827e4..5279b0c88e9c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -342,6 +342,13 @@ static bool
 intel_find_pll_ironlake_dp(const intel_limit_t *, struct drm_crtc *crtc,
                            int target, int refclk, intel_clock_t *best_clock);
 
+static inline u32 /* units of 100MHz */
+intel_fdi_link_freq(struct drm_device *dev)
+{
+        struct drm_i915_private *dev_priv = dev->dev_private;
+        return (I915_READ(FDI_PLL_BIOS_0) & FDI_PLL_FB_CLOCK_MASK) + 2;
+}
+
 static const intel_limit_t intel_limits_i8xx_dvo = {
         .dot = { .min = I8XX_DOT_MIN,           .max = I8XX_DOT_MAX },
         .vco = { .min = I8XX_VCO_MIN,           .max = I8XX_VCO_MAX },
@@ -3767,7 +3774,15 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
                                 target_clock = mode->clock;
                         else
                                 target_clock = adjusted_mode->clock;
-                        link_bw = 270000;
+
+                        /* FDI is a binary signal running at ~2.7GHz, encoding
+                         * each output octet as 10 bits. The actual frequency
+                         * is stored as a divider into a 100MHz clock, and the
+                         * mode pixel clock is stored in units of 1KHz.
+                         * Hence the bw of each lane in terms of the mode signal
+                         * is:
+                         */
+                        link_bw = intel_fdi_link_freq(dev) * MHz(100)/KHz(1)/10;
                 }
 
                 /* determine panel color depth */