linux-kernel - [PATCH 1/2] ASoC: stm32: sai: skip useless iterations on kernel rate loop

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Message-ID: <20250430165210.321273-2-olivier.moysan@foss.st.com>
Date: Wed, 30 Apr 2025 18:52:08 +0200
From: Olivier Moysan <olivier.moysan@...s.st.com>
To: Olivier Moysan <olivier.moysan@...s.st.com>,
        Arnaud Pouliquen
	<arnaud.pouliquen@...s.st.com>,
        Liam Girdwood <lgirdwood@...il.com>, Mark
 Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai
	<tiwai@...e.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre
 Torgue <alexandre.torgue@...s.st.com>
CC: <linux-sound@...r.kernel.org>, <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] ASoC: stm32: sai: skip useless iterations on kernel rate loop

the frequency of the kernel clock must be greater than or equal to the
bitclock rate. When searching for a convenient kernel clock rate in
stm32_sai_set_parent_rate() function, it is useless to continue the loop
below bitclock rate, as it will result in a invalid kernel clock rate.
Change the loop output condition.

Fixes: b1d2e4067dc6 ("ASoC: stm32: sai: add stm32mp25 support")
Signed-off-by: Olivier Moysan <olivier.moysan@...s.st.com>
---
 sound/soc/stm/stm32_sai_sub.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/sound/soc/stm/stm32_sai_sub.c b/sound/soc/stm/stm32_sai_sub.c
index e8c1abf1ae0a..4d018b4bc3f0 100644
--- a/sound/soc/stm/stm32_sai_sub.c
+++ b/sound/soc/stm/stm32_sai_sub.c
@@ -409,11 +409,11 @@ static int stm32_sai_set_parent_rate(struct stm32_sai_sub_data *sai,
 				     unsigned int rate)
 {
 	struct platform_device *pdev = sai->pdev;
-	unsigned int sai_ck_rate, sai_ck_max_rate, sai_curr_rate, sai_new_rate;
+	unsigned int sai_ck_rate, sai_ck_max_rate, sai_ck_min_rate, sai_curr_rate, sai_new_rate;
 	int div, ret;
 
 	/*
-	 * Set maximum expected kernel clock frequency
+	 * Set minimum and maximum expected kernel clock frequency
 	 * - mclk on or spdif:
 	 *   f_sai_ck = MCKDIV * mclk-fs * fs
 	 *   Here typical 256 ratio is assumed for mclk-fs
@@ -423,13 +423,16 @@ static int stm32_sai_set_parent_rate(struct stm32_sai_sub_data *sai,
 	 *   Set constraint MCKDIV * FRL <= 256, to ensure MCKDIV is in available range
 	 *   f_sai_ck = sai_ck_max_rate * pow_of_two(FRL) / 256
 	 */
+	sai_ck_min_rate = rate * 256;
 	if (!(rate % SAI_RATE_11K))
 		sai_ck_max_rate = SAI_MAX_SAMPLE_RATE_11K * 256;
 	else
 		sai_ck_max_rate = SAI_MAX_SAMPLE_RATE_8K * 256;
 
-	if (!sai->sai_mclk && !STM_SAI_PROTOCOL_IS_SPDIF(sai))
+	if (!sai->sai_mclk && !STM_SAI_PROTOCOL_IS_SPDIF(sai)) {
+		sai_ck_min_rate = rate * sai->fs_length;
 		sai_ck_max_rate /= DIV_ROUND_CLOSEST(256, roundup_pow_of_two(sai->fs_length));
+	}
 
 	/*
 	 * Request exclusivity, as the clock is shared by SAI sub-blocks and by
@@ -472,7 +475,7 @@ static int stm32_sai_set_parent_rate(struct stm32_sai_sub_data *sai,
 		/* Try a lower frequency */
 		div++;
 		sai_ck_rate = sai_ck_max_rate / div;
-	} while (sai_ck_rate > rate);
+	} while (sai_ck_rate >= sai_ck_min_rate);
 
 	/* No accurate rate found */
 	dev_err(&pdev->dev, "Failed to find an accurate rate");
-- 
2.25.1