On Mon, Mar 16, 2020 at 7:01 AM Daniel Baluta daniel.baluta@gmail.com wrote:
Thanks Rob for review. See my comments inline:
<snip>
+# SPDX-License-Identifier: GPL-2.0
Dual license new bindings please:
(GPL-2.0-only OR BSD-2-Clause)
Ok, will do.
+%YAML 1.2 +--- +$id: http://devicetree.org/schemas/sound/fsl,dai.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml#
+title: Generic CPU FSL DAI driver for resource management
Bindings are for h/w devices, not drivers.
Indeed. I think I will change it to something like this.
title: 'FSL CPU DAI for resource management'
The explanation are already in patch 2/2 of this series but let e explain again what I'm trying to do here and let me know if this makes sense to you.
Digital Audio Interface device (DAI) are configured by the firmware running on the DSP. The only trouble we have is that we cannot easily handle 'resources' like: clocks, pinctrl, power domains from firmware.
This is because our architecture is like this:
M core [running System Controller Firmware] | | A core [Linux]<----> DSP core [SOF firmware]
In theory, it is possible for DSP core to communicate with M core, but this needs a huge amount of work in order to make it work. We have this on our plans for the future, but we are now trying to do resource management from A core because the infrastructure is already in place.
When you change things in the future, Linux gets to keep supporting both ways of doing things? I'd rather just support one way.
So, the curent driver introduced in this series acts like a Generic resource driver for DAI device. We can have multiple types of DAIs but most of them need the same types of resources (clocks, pinctrl, pm) sof for this reason I made it generic.
+maintainers:
- Daniel Baluta daniel.baluta@nxp.com
+description: |
- On platforms with a DSP we need to split the resource handling between
- Application Processor (AP) and DSP. On platforms where the DSP doesn't
- have an easy access to resources, the AP will take care of
- configuring them. Resources handled by this generic driver are: clocks,
- power domains, pinctrl.
The DT should define a DSP node with resources that are part of the DSP. What setup the AP has to do should be implied by the compatible string and possibly what resources are described.
We already have a DSP node: Documentation/devicetree/bindings/dsp/fsl,dsp.yaml but I thought that the resources attached to DAIs are separated from the resources attached to the DSP device.
I'd agree if the DAI was fully described in the DT.
In the great scheme of ALSA we usually have things like this:
FE <-----> BE
In the SOF world FE are defined by topology framework. Back ends are defined by the machine driver:
On the BE side we have:
- codec -> this is the specific code
- platform -> this is the DSP
- cpu -> this is our Generic DAI device
Now, I'm wondering if we can get rid of cpu here and make platform node (dsp) take care of every resource (this looks not natural).
I would think about how the DT will look when the DSP manages all these resources itself and how the kernel drivers evolve. I think perhaps if you can get rid of the DT part and just define the resources in the driver, then the future transition would be easier.
Perhaps Mark, Liam or Pierre can help me with this.
Or maybe the audio portion of the DSP is a child node...
+properties:
- '#sound-dai-cells':
- const: 0
- compatible:
- enum:
- fsl,esai-dai- fsl,sai-daiNot very specific. There's only 2 versions of the DSP and ways it is integrated?
As I said above this is not about the DSP, but about the Digital Audio Intraface. On i.MX NXP boards we have two types of DAIs: SAI and ESAI.
<snip>
- pinctrl-0:
- description: Should specify pin control groups used for this controller.
- pinctrl-names:
- const: default
pinctrl properties are implicitly allowed an don't have to be listed here.
Great.
- power-domains:
- $ref: '/schemas/types.yaml#/definitions/phandle-array'
Don't need a type.
- description:
List of phandles and PM domain specifiers, as defined by bindings of thePM domain provider.Don't need to re-define common properties.
You do need to say how many power domains (maxItems: 1?).
We support multiple power domains, so technically there is no upper limit. What should I put here in this case?
There's an upper limit in the h/w so there should be some sort of limit.
- fsl,dai-index:
- $ref: '/schemas/types.yaml#/definitions/uint32'
- description: Physical DAI index, must match the index from topology file
Sorry, we don't do indexes in DT.
What's a topology file?
Topology files are binary blobs that contain the description of an audio pipeline. They are built are written in a specific format and compiled with alsa-tplg tools in userspace.
Then loaded via firmware interface inside the kernel.
Sounds like a kernel-userspace issue that has nothing to do with DT. How do other platforms deal with mulitple DAIs?
Rob