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    SubjectRe: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal to system freq
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    Hi Fabio,


    > [Sorry for the top-posting]
    >
    >
    > The driver currently has:
    >
    >
    > /*
    > * Hardware limitation: The bclk rate must be
    > * never greater than 1/5 IPG clock rate
    > */
    > if (freq * 5 > clk_get_rate(ssi_private->clk)) {
    > dev_err(cpu_dai->dev, "bitclk > ipgclk/5\n");
    > return -EINVAL;
    > }
    >

    Unfortunately not.

    This is the part of fsl_ssi_set_bclk() function which is called after
    fsl_ssi_set_dai_sysclk() (which sets ssi_private->bitclk_freq = freq;).

    Before the aforementioned check we do have:

    if (ssi_private->bitclk_freq)
    freq = ssi_private->bitclk_freq;
    else
    freq = params_channels(hw_params) * 32 * params_rate(hw_params);


    Which assigns freq = bitclk_freq (66 MHz)

    And then we break on this particular check:

    66MHz * 5 > 66 MHz.



    The culprit IMHO is the ssi_private->bitclk_freq = freq; in the
    fsl_ssi_set_dai_sysclk(), since we _should_ set SSI's IP block clock
    (ssi_private->clk), not the bit clock (BCLK).


    This patch just quits early if it detects change, which don't need to be
    done.

    >
    > Isn't this properly taking care of the clock restriction?
    >
    > ________________________________
    > From: Lukasz Majewski <lukma@denx.de>
    > Sent: Sunday, September 3, 2017 8:05:01 AM
    > To: Timur Tabi; Nicolin Chen; Xiubo Li; Fabio Estevam; Liam Girdwood; Mark Brown; Jaroslav Kysela; Takashi Iwai
    > Cc: alsa-devel@alsa-project.org; linuxppc-dev@lists.ozlabs.org; linux-kernel@vger.kernel.org; Lukasz Majewski
    > 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@denx.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
    >
    >


    --
    Best regards,

    Lukasz Majewski

    --
    DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
    HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
    Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de

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