[PATCH] clk: at91: optimize clk_round_rate() for AUDIO_PLL

* [PATCH] clk: at91: optimize clk_round_rate() for AUDIO_PLL
@ 2018-12-17 19:37 Michał Mirosław
       [not found] ` <154508897026.19322.14961293619238289668@swboyd.mtv.corp.google.com>
  0 siblings, 1 reply; 3+ messages in thread
From: Michał Mirosław @ 2018-12-17 19:37 UTC (permalink / raw)
  To: linux-clk, linux-arm-kernel
  Cc: Michael Turquette, Stephen Boyd, Nicolas Ferre,
	Alexandre Belloni, Ludovic Desroches

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>
---
 drivers/clk/at91/clk-audio-pll.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/at91/clk-audio-pll.c b/drivers/clk/at91/clk-audio-pll.c
index 36d77146a3bd..3a358282784e 100644
--- a/drivers/clk/at91/clk-audio-pll.c
+++ b/drivers/clk/at91/clk-audio-pll.c
@@ -340,7 +340,11 @@ 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);
+	for (div = max(best_parent_rate / rate, 1ul); 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 +354,8 @@ 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 */
 		}
 	}
 
-- 
2.19.2


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