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

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Message-ID: <47ceba83-1097-072e-bed6-d1964bce7a25@ti.com>
Date:   Wed, 2 Aug 2017 17:09:37 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Pierre Yves MORDRET <pierre-yves.mordret@...com>,
        Vinod Koul <vinod.koul@...el.com>
CC:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Russell King <linux@...linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        "M'boumba Cedric Madianga" <cedric.madianga@...il.com>,
        Fabrice GASNIER <fabrice.gasnier@...com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Fabien DESSENNE <fabien.dessenne@...com>,
        Amelie DELAUNAY <amelie.delaunay@...com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/5] dmaengine: Add STM32 DMAMUX driver

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.

- Péter