drm/i915: Make M/N checks non-fuzzy

Now that we no longer fuzz M/N during fastset these should
match exctly.

In order to get a match with what the BIOS does we need to round
M/N down. And we do the opposite rounding when doing the readback.
That gets us pretty much the same thing back.

There can still be slight rounding differences between FDI M/N
vs. the DPLL output so we allow for tiny deviation in
intel_pipe_config_sanity_check().

v2: Tweak rounding/sanity check stuff a bit

Reviewed-by: Jani Nikula <jani.nikula@intel.com> #v1
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220907091057.11572-10-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_display.c

@@ -4495,7 +4495,8 @@ int intel_dotclock_calculate(int link_freq,
 	if (!m_n->link_n)
 		return 0;
 
-	return div_u64(mul_u32_u32(m_n->link_m, link_freq), m_n->link_n);
+	return DIV_ROUND_UP_ULL(mul_u32_u32(m_n->link_m, link_freq),
+				m_n->link_n);
 }
 
 int intel_crtc_dotclock(const struct intel_crtc_state *pipe_config)
@@ -5387,47 +5388,15 @@ bool intel_fuzzy_clock_check(int clock1, int clock2)
 	return false;
 }
 
-static bool
-intel_compare_m_n(unsigned int m, unsigned int n,
-		  unsigned int m2, unsigned int n2,
-		  bool exact)
-{
-	if (m == m2 && n == n2)
-		return true;
-
-	if (exact || !m || !n || !m2 || !n2)
-		return false;
-
-	BUILD_BUG_ON(DATA_LINK_M_N_MASK > INT_MAX);
-
-	if (n > n2) {
-		while (n > n2) {
-			m2 <<= 1;
-			n2 <<= 1;
-		}
-	} else if (n < n2) {
-		while (n < n2) {
-			m <<= 1;
-			n <<= 1;
-		}
-	}
-
-	if (n != n2)
-		return false;
-
-	return intel_fuzzy_clock_check(m, m2);
-}
-
 static bool
 intel_compare_link_m_n(const struct intel_link_m_n *m_n,
-		       const struct intel_link_m_n *m2_n2,
-		       bool exact)
+		       const struct intel_link_m_n *m2_n2)
 {
 	return m_n->tu == m2_n2->tu &&
-		intel_compare_m_n(m_n->data_m, m_n->data_n,
-				  m2_n2->data_m, m2_n2->data_n, exact) &&
-		intel_compare_m_n(m_n->link_m, m_n->link_n,
-				  m2_n2->link_m, m2_n2->link_n, exact);
+		m_n->data_m == m2_n2->data_m &&
+		m_n->data_n == m2_n2->data_n &&
+		m_n->link_m == m2_n2->link_m &&
+		m_n->link_n == m2_n2->link_n;
 }
 
 static bool
@@ -5621,8 +5590,7 @@ intel_pipe_config_compare(const struct intel_crtc_state *current_config,
 
 #define PIPE_CONF_CHECK_M_N(name) do { \
 	if (!intel_compare_link_m_n(&current_config->name, \
-				    &pipe_config->name,\
-				    !fastset)) { \
+				    &pipe_config->name)) { \
 		pipe_config_mismatch(fastset, crtc, __stringify(name), \
 				     "(expected tu %i data %i/%i link %i/%i, " \
 				     "found tu %i, data %i/%i link %i/%i)", \
@@ -5669,9 +5637,9 @@ intel_pipe_config_compare(const struct intel_crtc_state *current_config,
  */
 #define PIPE_CONF_CHECK_M_N_ALT(name, alt_name) do { \
 	if (!intel_compare_link_m_n(&current_config->name, \
-				    &pipe_config->name, !fastset) && \
+				    &pipe_config->name) && \
 	    !intel_compare_link_m_n(&current_config->alt_name, \
-				    &pipe_config->name, !fastset)) { \
+				    &pipe_config->name)) { \
 		pipe_config_mismatch(fastset, crtc, __stringify(name), \
 				     "(expected tu %i data %i/%i link %i/%i, " \
 				     "or tu %i data %i/%i link %i/%i, " \

drivers/gpu/drm/i915/display/intel_modeset_verify.c

@@ -94,10 +94,10 @@ static void intel_pipe_config_sanity_check(struct drm_i915_private *dev_priv,
 
 		/*
 		 * FDI already provided one idea for the dotclock.
-		 * Yell if the encoder disagrees.
+		 * Yell if the encoder disagrees. Allow for slight
+		 * rounding differences.
 		 */
-		drm_WARN(&dev_priv->drm,
-			 !intel_fuzzy_clock_check(fdi_dotclock, dotclock),
+		drm_WARN(&dev_priv->drm, abs(fdi_dotclock - dotclock) > 1,
 			 "FDI dotclock and encoder dotclock mismatch, fdi: %i, encoder: %i\n",
 			 fdi_dotclock, dotclock);
 	}