drm/i915: Make sure we respect n.max on VLV

We limit the maximum n divider value in order to make sure the PLL's
reference inout is at least 19.2 MHz. I assume that is done to satisfy
some hardware requirement.

However we never check whether that calculated limit is below the
maximum supoorted N divider value (7). In practice that is always true
since we only support 100 MHz reference clock, but making the code
safe against higher reference clocks seems like a reasoanble thing to
do.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 62cfada..ed95eb2 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -678,15 +678,16 @@ vlv_find_best_dpll(const intel_limit_t *limit, struct drm_crtc *crtc,
                   intel_clock_t *best_clock)
 {
        intel_clock_t clock;
-       u32 minupdate = 19200;
        unsigned int bestppm = 1000000;
+       /* min update 19.2 MHz */
+       int max_n = min(limit->n.max, refclk / 19200);
 
        target *= 5; /* fast clock */
 
        memset(best_clock, 0, sizeof(*best_clock));
 
        /* based on hardware requirement, prefer smaller n to precision */
-       for (clock.n = limit->n.min; clock.n <= ((refclk) / minupdate); clock.n++) {
+       for (clock.n = limit->n.min; clock.n <= max_n; clock.n++) {
                for (clock.p1 = limit->p1.max; clock.p1 > limit->p1.min; clock.p1--) {
                        for (clock.p2 = limit->p2.p2_fast; clock.p2 > 0;
                             clock.p2 -= clock.p2 > 10 ? 2 : 1) {