drm/i915: Fix and cleanup DPLL calculation for Ironlake

When the ideal error range can't be reached, this will safely use
a most closed one. Clean up some dumb codes in DPLL function too.

This fixes DPLL clock issue against one monitor at 1680x1050@60hz.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

1 files changed, 6 insertions, 9 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3ba6546b7c7f..099f420de57a 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -863,10 +863,8 @@ intel_igdng_find_best_PLL(const intel_limit_t *limit, struct drm_crtc *crtc,
         struct drm_device *dev = crtc->dev;
         struct drm_i915_private *dev_priv = dev->dev_private;
         intel_clock_t clock;
-        int max_n;
-        bool found;
         int err_most = 47;
-        found = false;
+        int err_min = 10000;
 
         /* eDP has only 2 clock choice, no n/m/p setting */
         if (HAS_eDP)
@@ -890,10 +888,9 @@ intel_igdng_find_best_PLL(const intel_limit_t *limit, struct drm_crtc *crtc,
         }
 
         memset(best_clock, 0, sizeof(*best_clock));
-        max_n = limit->n.max;
         for (clock.p1 = limit->p1.max; clock.p1 >= limit->p1.min; clock.p1--) {
                 /* based on hardware requriment prefer smaller n to precision */
-                for (clock.n = limit->n.min; clock.n <= max_n; clock.n++) {
+                for (clock.n = limit->n.min; clock.n <= limit->n.max; clock.n++) {
                         /* based on hardware requirment prefere larger m1,m2 */
                         for (clock.m1 = limit->m1.max;
                              clock.m1 >= limit->m1.min; clock.m1--) {
@@ -907,18 +904,18 @@ intel_igdng_find_best_PLL(const intel_limit_t *limit, struct drm_crtc *crtc,
                                         this_err = abs((10000 - (target*10000/clock.dot)));
                                         if (this_err < err_most) {
                                                 *best_clock = clock;
-                                                err_most = this_err;
-                                                max_n = clock.n;
-                                                found = true;
                                                 /* found on first matching */
                                                 goto out;
+                                        } else if (this_err < err_min) {
+                                                *best_clock = clock;
+                                                err_min = this_err;
                                         }
                                 }
                         }
                 }
         }
 out:
-        return found;
+        return true;
 }
 
 /* DisplayPort has only two frequencies, 162MHz and 270MHz */