drm/i915: Allow fuzzy matching in intel_compare_link_m_n

This prevents a unnecessary modeset on a dell XPS 13 (2016).

N is always a power of 2, which means that for fuzzy matching we should
compare for inequality on the n values, then do fuzzy matching on the m
values.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Tested-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/568D0E93.304@linux.intel.com

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 043adfa..ab0b406 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12577,19 +12577,22 @@ intel_compare_m_n(unsigned int m, unsigned int n,
 
        BUILD_BUG_ON(DATA_LINK_M_N_MASK > INT_MAX);
 
-       if (m > m2) {
-               while (m > m2) {
+       if (n > n2) {
+               while (n > n2) {
                        m2 <<= 1;
                        n2 <<= 1;
                }
-       } else if (m < m2) {
-               while (m < m2) {
+       } else if (n < n2) {
+               while (n < n2) {
                        m <<= 1;
                        n <<= 1;
                }
        }
 
-       return m == m2 && n == n2;
+       if (n != n2)
+               return false;
+
+       return intel_fuzzy_clock_check(m, m2);
 }
 
 static bool