linux-kernel - [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal to system freq

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Date:   Sun,  3 Sep 2017 13:05:01 +0200
From:   Lukasz Majewski <lukma@...x.de>
To:     Timur Tabi <timur@...i.org>, Nicolin Chen <nicoleotsuka@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc:     alsa-devel@...a-project.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Lukasz Majewski <lukma@...x.de>
Subject: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal to system freq

The problem is visible in the following setup (on the imx6q):
"simple-audio-card" -> ssi2 -> I2S + I2C -> codec

The function call log (simple-card probe -> CONFIG_SND_SIMPLE_CARD):

asoc_simple_card_init_dai() @ sound/soc/generic/simple-card-utils.c
snd_soc_dai_set_sysclk()
fsl_ssi_set_dai_sysclk() @ sound/soc/fsl/fsl_ssi.c

The last call is changing the bit clock (BCLK) frequency to SSI's IP
block clock (ipg = 66 MHz) [1].
This is wrong, since IMX SSI block requires the I2S BCLK to be less
than 1/5 of [1].

As a result the driver initialization passes without any errors, but the
speaker-test test case breaks.

This commit checks if the fsl_ssi_set_dai_sysclk() frequency passed is
not equal to [1].

Signed-off-by: Lukasz Majewski <lukma@...x.de>
---
 sound/soc/fsl/fsl_ssi.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
index 173cb84..1186fa9 100644
--- a/sound/soc/fsl/fsl_ssi.c
+++ b/sound/soc/fsl/fsl_ssi.c
@@ -809,6 +809,8 @@ static int fsl_ssi_set_dai_sysclk(struct snd_soc_dai *cpu_dai,
 		int clk_id, unsigned int freq, int dir)
 {
 	struct fsl_ssi_private *ssi_private = snd_soc_dai_get_drvdata(cpu_dai);
+	if (clk_get_rate(ssi_private->clk) == freq)
+		return 0;
 
 	ssi_private->bitclk_freq = freq;
 
-- 
2.1.4