clk: at91: optimize clk_round_rate() for AUDIO_PLL

Stop the search for parent rate when exact match is found.

This makes for 3 clk_round_rate() calls instead of 64 of them on
SAMA5D2-based board when searching for 12.288MHz clock.
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Reviewed-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/at91/clk-audio-pll.c

@@ -340,7 +340,12 @@ static long clk_audio_pll_pmc_round_rate(struct clk_hw *hw, unsigned long rate,
 	pr_debug("A PLL/PMC: %s, rate = %lu (parent_rate = %lu)\n", __func__,
 		 rate, *parent_rate);
 
-	for (div = 1; div <= AUDIO_PLL_QDPMC_MAX; div++) {
+	if (!rate)
+		return 0;
+
+	best_parent_rate = clk_round_rate(pclk->clk, 1);
+	div = max(best_parent_rate / rate, 1UL);
+	for (; div <= AUDIO_PLL_QDPMC_MAX; div++) {
 		best_parent_rate = clk_round_rate(pclk->clk, rate * div);
 		tmp_rate = best_parent_rate / div;
 		tmp_diff = abs(rate - tmp_rate);
@@ -350,6 +355,8 @@ static long clk_audio_pll_pmc_round_rate(struct clk_hw *hw, unsigned long rate,
 			best_rate = tmp_rate;
 			best_diff = tmp_diff;
 			tmp_qd = div;
+			if (!best_diff)
+				break;	/* got exact match */
 		}
 	}