drm/i915: Don't warn about zero N/P in *_calc_dpll_params()

Allow *_calc_dpll_params() to be called even if the N/P dividers
are zero without warning. We'll want to call these to make sure the
derived values are fully computed, but not all users (VLV DSI in
particular) even enable the DPLL and thus the dividers will
be left at zero.

It could also be possible that the BIOS has misprogrammed the DPLL
(IIRC happened with some SNB machines with 4k+ displays) and thus
we'll currently generate a lot of dmesg spew. Better be silent and
just let the normal state checker/etc. deal with any driver bugs.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230705202122.17915-5-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -314,10 +314,11 @@ int pnv_calc_dpll_params(int refclk, struct dpll *clock)
 {
 	clock->m = clock->m2 + 2;
 	clock->p = clock->p1 * clock->p2;
-	if (WARN_ON(clock->n == 0 || clock->p == 0))
-		return 0;
-	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
-	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
+
+	clock->vco = clock->n == 0 ? 0 :
+		DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
+	clock->dot = clock->p == 0 ? 0 :
+		DIV_ROUND_CLOSEST(clock->vco, clock->p);
 
 	return clock->dot;
 }
@@ -331,10 +332,11 @@ int i9xx_calc_dpll_params(int refclk, struct dpll *clock)
 {
 	clock->m = i9xx_dpll_compute_m(clock);
 	clock->p = clock->p1 * clock->p2;
-	if (WARN_ON(clock->n + 2 == 0 || clock->p == 0))
-		return 0;
-	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n + 2);
-	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
+
+	clock->vco = clock->n + 2 == 0 ? 0 :
+		DIV_ROUND_CLOSEST(refclk * clock->m, clock->n + 2);
+	clock->dot = clock->p == 0 ? 0 :
+		DIV_ROUND_CLOSEST(clock->vco, clock->p);
 
 	return clock->dot;
 }
@@ -343,10 +345,11 @@ int vlv_calc_dpll_params(int refclk, struct dpll *clock)
 {
 	clock->m = clock->m1 * clock->m2;
 	clock->p = clock->p1 * clock->p2 * 5;
-	if (WARN_ON(clock->n == 0 || clock->p == 0))
-		return 0;
-	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
-	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
+
+	clock->vco = clock->n == 0 ? 0 :
+		DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
+	clock->dot = clock->p == 0 ? 0 :
+		DIV_ROUND_CLOSEST(clock->vco, clock->p);
 
 	return clock->dot;
 }
@@ -355,11 +358,11 @@ int chv_calc_dpll_params(int refclk, struct dpll *clock)
 {
 	clock->m = clock->m1 * clock->m2;
 	clock->p = clock->p1 * clock->p2 * 5;
-	if (WARN_ON(clock->n == 0 || clock->p == 0))
-		return 0;
-	clock->vco = DIV_ROUND_CLOSEST_ULL(mul_u32_u32(refclk, clock->m),
-					   clock->n << 22);
-	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
+
+	clock->vco = clock->n == 0 ? 0 :
+		DIV_ROUND_CLOSEST_ULL(mul_u32_u32(refclk, clock->m), clock->n << 22);
+	clock->dot = clock->p == 0 ? 0 :
+		DIV_ROUND_CLOSEST(clock->vco, clock->p);
 
 	return clock->dot;
 }