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

[Rob Herring <robh@kernel.org>]

On Sat, Sep 4, 2021 at 9:51 AM Daniel Baluta <daniel.baluta@gmail.com> wrote:
>
> On Fri, Sep 3, 2021 at 8:11 PM Rob Herring <robh@kernel.org> wrote:
> >
> > On Fri, Sep 03, 2021 at 05:53:40PM +0300, Daniel Baluta wrote:
> > > From: Daniel Baluta <daniel.baluta@nxp.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@nxp.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).

'status' is how you disable a device to not be used by the OS.

The information about that device's resources are already in DT, we
don't need to duplicate that here. If you want a list of devices
assigned to the DSP here, that would be okay.

> 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

No, that's certainly not what I was suggesting. The resources in the
DSP node should be the h/w resources of the DSP itself.

Rob