clk: k210: Try harder to get the best config

In some cases, the best config cannot be used because the VCO would be
out-of-spec. In these cases, we may need to try a worse combination of r/od
in order to find the best representable config. This also adds a few test
cases to catch this and other (possible) unlikely errors.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/clk/clk_kendryte.c

@@ -816,6 +816,30 @@ again:
 				i--;
 			}
 
+			/*
+			 * Try looking back to see if there is a worse ratio
+			 * that we could try anyway
+			 */
+			while (i > 0) {
+				i--;
+				new_r = UNPACK_R(factors[i]);
+				new_od = UNPACK_OD(factors[i]);
+				/*
+				 * Don't loop over factors for the same product
+				 * to avoid getting stuck because of the above
+				 * clause
+				 */
+				if (r * od != new_r * new_od) {
+					if (new_r * new_od > last_r * last_od) {
+						r = new_r;
+						od = new_od;
+						swapped = false;
+						goto again;
+					}
+					break;
+				}
+			}
+
 			/* We ran out of things to try */
 			continue;
 		}

test/dm/k210_pll.c

@@ -84,6 +84,10 @@ static int dm_test_k210_pll(struct unit_test_state *uts)
 	compare(400000000, 26000000);
 	compare(27000000, 26000000);
 	compare(26000000, 27000000);
+	compare(13300000 * 64, 13300000);
+	compare(21250000, 21250000 * 70);
+	compare(21250000, 1750000000);
+	compare(1750000000, 1750000000);
 
 	return 0;
 }