linux-kernel - [PATCH v3 1/1] ASoC: fsl_asrc: make sure the input and output clocks are different

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Message-Id: <20200717103857.31877-2-arnaud.ferraris@collabora.com>
Date:   Fri, 17 Jul 2020 12:38:58 +0200
From:   Arnaud Ferraris <arnaud.ferraris@...labora.com>
To:     alsa-devel@...a-project.org
Cc:     Timur Tabi <timur@...nel.org>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <festevam@...il.com>,
        Shengjiu Wang <shengjiu.wang@...il.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        kernel@...labora.com,
        Arnaud Ferraris <arnaud.ferraris@...labora.com>
Subject: [PATCH v3 1/1] ASoC: fsl_asrc: make sure the input and output clocks are different

The current clock selection algorithm might select the same clock for
both input and output when, for instance, the output sample rate is a
multiple of the input rate.

In that case, both selectable clocks will be multiples of both the input
and output sample rates, and therefore the first of these clocks will be
selected for both input and output, leading to miscalculation of the
dividers for either the input or output side.

Example:
  Input uses clock A (512kHz) and has a sample rate of 8kHz
  Output uses clock B (1024kHz) and has a sample rate of 16kHz

  In this case, the algorithm will select clock A for both input and
  output: the input divider will therefore be calculated properly
  (512 / 8 => 64), but the output divider's value will be only half
  the expected value (512 / 16 => 32 instead of 1024 / 16 => 64).

This patch makes sure it always selects distinct input and output
clocks.

Signed-off-by: Arnaud Ferraris <arnaud.ferraris@...labora.com>
---
 sound/soc/fsl/fsl_asrc.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/sound/soc/fsl/fsl_asrc.c b/sound/soc/fsl/fsl_asrc.c
index 02c81d2e34ad..de10c208d3c8 100644
--- a/sound/soc/fsl/fsl_asrc.c
+++ b/sound/soc/fsl/fsl_asrc.c
@@ -608,8 +608,8 @@ static void fsl_asrc_select_clk(struct fsl_asrc_priv *asrc_priv,
 {
 	struct fsl_asrc_pair_priv *pair_priv = pair->private;
 	struct asrc_config *config = pair_priv->config;
-	int rate[2], select_clk[2]; /* Array size 2 means IN and OUT */
-	int clk_rate, clk_index;
+	int rate[2], select_clk[2], clk_index[2]; /* Array size 2 means IN and OUT */
+	int clk_rate;
 	int i = 0, j = 0;
 
 	rate[IN] = in_rate;
@@ -618,11 +618,15 @@ static void fsl_asrc_select_clk(struct fsl_asrc_priv *asrc_priv,
 	/* Select proper clock source for internal ratio mode */
 	for (j = 0; j < 2; j++) {
 		for (i = 0; i < ASRC_CLK_MAP_LEN; i++) {
-			clk_index = asrc_priv->clk_map[j][i];
-			clk_rate = clk_get_rate(asrc_priv->asrck_clk[clk_index]);
-			/* Only match a perfect clock source with no remainder */
+			clk_index[j] = asrc_priv->clk_map[j][i];
+			clk_rate = clk_get_rate(asrc_priv->asrck_clk[clk_index[j]]);
+			/*
+			 * Only match a perfect clock source with no remainder
+			 * and make sure the input & output clocks are different
+			 */
 			if (clk_rate != 0 && (clk_rate / rate[j]) <= 1024 &&
-			    (clk_rate % rate[j]) == 0)
+			    (clk_rate % rate[j]) == 0 &&
+			    (j == 0 || clk_index[j] != clk_index[j - 1]))
 				break;
 		}
 
-- 
2.27.0