linux-kernel - Re: [PATCH v2 2/2] dt-bindings: dsp: fsl: Add DSP optional clocks documentation

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Message-ID: <CAEnQRZC-GN9iEPk6-A_oKPHcCYj8_WeQC0TT_NpK_QntkmAqiQ@mail.gmail.com>
Date:   Sat, 4 Sep 2021 17:50:56 +0300
From:   Daniel Baluta <daniel.baluta@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Daniel Baluta <daniel.baluta@....nxp.com>,
        Mark Brown <broonie@...nel.org>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Devicetree List <devicetree@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        Péter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        s-anna@...com, Daniel Baluta <daniel.baluta@....com>
Subject: Re: [PATCH v2 2/2] dt-bindings: dsp: fsl: Add DSP optional clocks documentation

On Fri, Sep 3, 2021 at 8:11 PM Rob Herring <robh@...nel.org> wrote:
>
> On Fri, Sep 03, 2021 at 05:53:40PM +0300, Daniel Baluta wrote:
> > From: Daniel Baluta <daniel.baluta@....com>
> >
> > DSP node on the Linux kernel side must also take care of enabling
> > DAI/DMA related clocks.
> >
> > By design we choose to manage DAI/DMA clocks from the kernel side because of
> > the architecture of some i.MX8 boards.
> >
> > Clocks are handled by a special M4 core which runs a special firmware
> > called SCFW (System Controler firmware).
> >
> > This communicates with A cores running Linux via a special Messaging
> > Unit and implements a custom API which is already implemented by the
> > Linux kernel i.MX clocks implementation.
> >
> > Note that these clocks are optional. We can use the DSP without them.
> >
> > Signed-off-by: Daniel Baluta <daniel.baluta@....com>
> > ---
> >  .../devicetree/bindings/dsp/fsl,dsp.yaml      | 33 +++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/dsp/fsl,dsp.yaml b/Documentation/devicetree/bindings/dsp/fsl,dsp.yaml
> > index 7afc9f2be13a..1453668c0194 100644
> > --- a/Documentation/devicetree/bindings/dsp/fsl,dsp.yaml
> > +++ b/Documentation/devicetree/bindings/dsp/fsl,dsp.yaml
> > @@ -24,16 +24,49 @@ properties:
> >      maxItems: 1
> >
> >    clocks:
> > +    minItems: 3
> >      items:
> >        - description: ipg clock
> >        - description: ocram clock
> >        - description: core clock
> > +      - description: esai0 core clock for accessing registers
> > +      - description: esai0 baud clock
> > +      - description: esai0 system clock
> > +      - description: esai0 spba clock required when ESAI is placed in slave mode
> > +      - description: SAI1 bus clock
> > +      - description: SAI1 master clock 0
> > +      - description: SAI1 master clock 1
> > +      - description: SAI1 master clock 2
> > +      - description: SAI1 master clock 3
> > +      - description: SAI3 bus clock
> > +      - description: SAI3 master clock 0
> > +      - description: SAI3 master clock 1
> > +      - description: SAI3 master clock 2
> > +      - description: SAI3 master clock 3
> > +      - description: SDMA3 root clock used for accessing registers
>
> Sigh, I just rejected this kind of thing for the other i.MX8 DSP
> binding[1].
>
> Add a reference to the h/w block and then get the clocks (and other
> resources) from there.

The H/W block is controlled by the DSP firmware. So, we don't want
to use the Linux kernel driver (thus the H/W block device tree node).

The only thing that we cannot control from the DSP firmware are the clocks
hence we handle them in the DSP node.

We moved the DAI clocks under the DSP node as I think you suggested here:

https://www.lkml.org/lkml/2020/3/12/969