linux-kernel - Re: [RFC 1/3] dt-bindings: dma: Add documentation for DMA domains

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Message-ID: <20190912170312.GD4392@vkoul-mobl>
Date:   Thu, 12 Sep 2019 22:33:12 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     robh+dt@...nel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, dan.j.williams@...el.com,
        devicetree@...r.kernel.org
Subject: Re: [RFC 1/3] dt-bindings: dma: Add documentation for DMA domains

On 09-09-19, 09:30, Peter Ujfalusi wrote:

> >> or domain-dma-controller?
> > 
> > I feel dma-domain-controller sounds fine as we are defining domains for
> > dmaengine. Another thought which comes here is that why not extend this to
> > slave as well and define dma-domain-controller for them as use that for
> > filtering, that is what we really need along with slave id in case a
> > specific channel is to be used by a peripheral
> > 
> > Thoughts..?
> 
> I have thought about this, we should be able to drop the phandle to the
> dma controller from the slave binding just fine.
> 
> However we have the dma routers for the slave channels and there is no
> clear way to handle them.
> They are not needed for non slave channels as there is no trigger to
> route. In DRA7 for example we have an event router for EDMA and another
> one for sDMA. If a slave device is to be serviced by EDMA, the EDMA
> event router needs to be specified, for sDMA clients should use the sDMA
> event router.

So you have dma, xbar and client? And you need to use a specfic xbar,
did i get that right?

> In DRA7 case we don't really have DMA controllers for domains, but we
> use the DMA which can service the peripheral better (sDMA is better to
> be used for UART, but can not be used for McASP for example)
> 
> Then we have the other type of DMA router for daVinci/am33xx/am43xx
> where the crossbar is not for the whole EDMA controller like in DRA7,
> but we have small crossbars for some channels.
> 
> Other vendors have their own dma router topology..
> 
> Too many variables to handle the cases without gotchas, which would need
> heavy churn in the core or in drivers.

-- 
~Vinod