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

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Date:   Tue, 5 Sep 2017 11:11:09 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Łukasz Majewski <lukma@...x.de>
Cc:     Fabio Estevam <fabio.estevam@....com>, Timur Tabi <timur@...i.org>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "festevam@...il.com" <festevam@...il.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal
 to system freq

On Tue, Sep 05, 2017 at 10:35:34AM +0200, Łukasz Majewski wrote:

> >And apparently, we shouldn't set bitclk to 66MHz either. Can
> >you help to find where this 66MHz comes from?

> 2. int asoc_simple_card_init_dai() @ simple-card-utils.c

Oh, I just searched in the simple-card.c but missed this file.

> In this function (point 2.) the
> simple_dai->sysclk is set and:
> snd_soc_dai_set_sysclk(dai, 0, simple_dai->sysclk, 0)
> which sets frequency to 66 MHz [*].
> 
> The asoc_simple_card_init_dai() is called in
> asoc_simple_card_dai_init() @ simple-card.c
> which is assigned to dai_link->init
> dai_link->init		= asoc_simple_card_dai_init; @ simple_card.c
> 
> And the sysclk itself is defined at:
> -------------------------------------
> dai_props->codec_dai->sysclk, which is used at:a

Why codec_dai? Why not dai_props->cpu_dai->sysclk since we are talking
about SSI?

> asoc_simple_card_startup(), asoc_simple_card_shutdown() and others
> functions at simple-card.c
> It is setup at:
> asoc_simple_card_parse_clk() @ simple-card-utils.c from macro:
> #define asoc_simple_card_parse_clk_cpu()
> And the problem is:
> -------------------
> 
> At the
> asoc_simple_card_parse_clk()
> we finally go to dts node:
> /soc/aips-bus@...00000/i2c@...a0000/tfa9879@6C

This tfa9879 should be the CODEC right?

> which has clock from I2C (66 MHz).

You mean I2C scl or I2S sclk?

-----------------------------------------------------------------

But anyway, I feel very confused here as you have 66MHz clock rate
(regardless of it purpose) for a codec dai but it's been passed to
a cpu dai (SSI).

> [*] - I could workaround this problem by setting:
> 
> system-clock-frequency = <0> in
> 
> 			dailink_master: cpu {
> 			    sound-dai = <&ssi2>;
> 			};
> 
> but this is IMHO even worse hack.... than this patch.

I haven't used simple-card for a while so I forgot how to define
its DT bindings specifically. But you should assign ssi2 as the
CPU dai and assign tfa9879 as a CODEC dai.