linux-kernel - Re: [alsa-devel] [PATCH] ASoC: fsl: sai: Fix clock source for mclk0

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Date:   Sun, 21 Apr 2019 11:40:12 +0300
From:   Daniel Baluta <daniel.baluta@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     Daniel Baluta <daniel.baluta@....com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "timur@...nel.org" <timur@...nel.org>,
        "Xiubo.Lee@...il.com" <Xiubo.Lee@...il.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "S.j. Wang" <shengjiu.wang@....com>,
        "tiwai@...e.com" <tiwai@...e.com>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        dl-linux-imx <linux-imx@....com>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel] [PATCH] ASoC: fsl: sai: Fix clock source for mclk0

On Sun, Apr 21, 2019 at 11:26 AM Nicolin Chen <nicoleotsuka@...il.com> wrote:
>
> On Sun, Apr 21, 2019 at 01:04:39AM -0700, Nicolin Chen wrote:
> > On Sun, Apr 21, 2019 at 10:26:40AM +0300, Daniel Baluta wrote:
> > > > Firstly, according to your commit message, neither imx8qm nor
> > > > imx6sx has an "mclk0" clock in the clock list. Either of them
> > > > starts with "mclk1". So, before you change the driver, I don't
> > > > think it's even a right thing to define an "mclk0" in the DT.
> > >
> > > From what I understand mclk0 means option 00b of MSEL bits which is:
> > > * busclk for i.MX8
> > > * mclk1 for i.MX6/7.
> >
> > MSEL bit is used for an internal clock MUX to select four clock
> > inputs. However,  these four clock inputs aren't exactly 1:1 of
> > SAI's inputs. As fas as I can tell, SAI only has one bus clock
> > and three MCLK[1-3]; the internal clock MUX maps the bus clock
> > or MCLK1 to its input0, and then linearly maps MCLK[1-3] to its
> > inputs[1-3]. So it doesn't sound right to me that you define an
> > "MCLK0" in the DT, as it's supposed to describe input clocks of
> > SAI block, other than its internal clock MUX's.
>
> Daniel, I think I's saying this too confident, though I do feel
> so :) But if you can prove me wrong and justify that there is an
> "MCLK0" as an external input of the SAI block, I will agree with
> this change.

Thanks a lot Nicolin for your input on this! Really appreciate it.
Let me have some time to further investigate it and really figure
out what happens at the hardware level.

thanks,
Daniel.