Re: [PATCH v3 2/5] dmaengine: Add STM32 DMAMUX driver

From: Peter Ujfalusi
Date: Wed Aug 02 2017 - 10:10:26 EST

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

On 2017-08-02 16:11, Pierre Yves MORDRET wrote:
Our SoC works with or without DMAMUX. Both binding is allowed. Using only DMA a
ChannelId and request line is part of the binding.

In our case the am335x's eDMA can work with or without the router, we only use the router node if we need none default event for a given DMA request line.

Using DMAMUx now the request
line is coming from dma_spec forwards to dma-master as well explained by Peter.
However ChannelID is now given by dma_get_any_slave_channel instead of bindings.
DMAMUX driver has to be aware of this ID to route request line to out DMA
channel. This channel id information is carried on until DMAMUX through
dmaengine_slave_config with a custom API.
Hope it clarifies the need.

I see, this is not much different then what we face with our dra7 devices. In theory we could use direct DMA binding to the DMA controller itself, but some requests would not be reachable, so we always use the router's node for DMA on dra7 family.

Basically the router would manage the ChannelID and create 'st,stm32-dma' compatible dma_spec (the four parameters).
Afaik you could have 3 parameters for the router and create a four parameter dma_spec, where the ChannelID is dynamically allocated.
But you need to convert all peripherals to use the router's node for the DMA.

- PÃter