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

From: Pierre Yves MORDRET
Date: Wed Aug 02 2017 - 10:29:36 EST

On 08/02/2017 04:09 PM, Peter Ujfalusi wrote:
> 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.

Correct router needs 3 parameters and among those 2 are forwarded though out
dma_spec. But when you say "ChannelID is dynamically allocated" you mean
dma_get_any_slave_channel ? If yes I can use the already existing bindings to
carry the channelID to DMA. No changes need to peripheral...

> But you need to convert all peripherals to use the router's node for the
> DMA.
> - PÃter