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

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Message-ID: <0e16a519-3d60-f683-5517-12a520e0e521@st.com>
Date:   Wed, 2 Aug 2017 16:28:40 +0200
From:   Pierre Yves MORDRET <pierre-yves.mordret@...com>
To:     Peter Ujfalusi <peter.ujfalusi@...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



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.
> 
> - Péter
> 

Py