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From: Peter Ujfalusi <>
To: Rob Herring <>
Cc: <>, <>,
	<>, <>,
Subject: Re: [PATCH 1/3] dt-bindings: dma: Add documentation for DMA domains
Date: Tue, 24 Sep 2019 16:56:32 +0300
Message-ID: <> (raw)
In-Reply-To: <>

On 16/09/2019 14.21, Peter Ujfalusi wrote:
> On 13/09/2019 17.36, Rob Herring wrote:
>> On Tue, Sep 10, 2019 at 02:50:35PM +0300, Peter Ujfalusi wrote:
>>> 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...
>> 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?

- Péter

>>> Signed-off-by: Peter Ujfalusi <>
>>> ---
>>>  .../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
> - Péter
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

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

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-10 11:50 [PATCH 0/3] dmaengine: Support for DMA domain controllers Peter Ujfalusi
2019-09-10 11:50 ` [PATCH 1/3] dt-bindings: dma: Add documentation for DMA domains Peter Ujfalusi
2019-09-13 14:36   ` Rob Herring
2019-09-16 11:21     ` Peter Ujfalusi
2019-09-24 13:56       ` Peter Ujfalusi [this message]
2019-09-24 14:44       ` Rob Herring
2019-10-04 15:56         ` Peter Ujfalusi
2019-09-10 11:50 ` [PATCH 2/3] dmaengine: of_dma: Function to look up the DMA domain of a client Peter Ujfalusi
2019-09-10 11:50 ` [PATCH 3/3] dmaengine: Support for requesting channels preferring DMA domain controller Peter Ujfalusi

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