Re: [PATCH 1/3] dt-bindings: dma: Add documentation for DMA domains

On 16/09/2019 14.21, Peter Ujfalusi wrote:

On 13/09/2019 17.36, Rob Herring wrote:

quoted

On Tue, Sep 10, 2019 at 02:50:35PM +0300, Peter Ujfalusi wrote:

quoted

On systems where multiple DMA controllers available, non Slave (for example
memcpy operation) users can not be described in DT as there is no device
involved from the DMA controller's point of view, DMA binding is not usable.
However in these systems still a peripheral might need to be serviced by or
it is better to serviced by specific DMA controller.
When a memcpy is used to/from a memory mapped region for example a DMA in the
same domain can perform better.
For generic software modules doing mem 2 mem operations it also matter that
they will get a channel from a controller which is faster in DDR to DDR mode
rather then from the first controller happen to be loaded.

This property is inherited, so it may be specified in a device node or in any
of its parent nodes.

If a device needs mem2mem dma, I think we should just use the existing 
dma binding. The provider will need a way to define cell values which 
mean mem2mem.

But isn't it going to be an abuse of the binding? Each DMA controller
would hack this in different ways, probably using out of range DMA
request/trigger number or if they have direction in the binding or some
other parameter would be set to something invalid...

quoted

For generic s/w, it should be able to query the dma speed or get a 
preferred one IMO. It's not a DT problem.

We measure memcpy speeds at boot time to select the fastest 
implementation for a chip, why not do that for mem2mem DMA?

It would make an impact on boot time since the tests would need to be
done with a large enough copy to be able to see clearly which one is faster.

Also we should be able to handle different probing orders:
client1 should have mem2mem channel from dma2.

- dma1 probes
- client1 probes and asks for a mem2mem channel
- dma2 probes

Here client1 should deffer until dma2 is probed.

Probably the property should be dma-mem2mem-domain to be more precise on
it's purpose and avoid confusion?

Is it OK if I go with dma-mem2mem-domain or dma-mem2mem-controller for
v2, but keeping the logic and approach intact?

Regards,
- Péter

quoted

quoted

Signed-off-by: Peter Ujfalusi <redacted>
---
 .../devicetree/bindings/dma/dma-domain.yaml   | 88 +++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/dma/dma-domain.yaml

Note that you have several errors in your schema. Run 'make dt_bindings_check'.

That does not do anything on my system, but git dt-doc-validate running
via https://github.com/robherring/yaml-bindings.git.

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki