linux-kernel - Re: [PATCH 5/6] dma-mapping: support fsl-mc bus

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Date:   Mon, 5 Mar 2018 19:39:38 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>, Nipun Gupta <nipun.gupta@....com>,
        will.deacon@....com, mark.rutland@....com, catalin.marinas@....com,
        iommu@...ts.linux-foundation.org, robh+dt@...nel.org,
        m.szyprowski@...sung.com, gregkh@...uxfoundation.org,
        joro@...tes.org, leoyang.li@....com, shawnguo@...nel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, bharat.bhushan@....com,
        stuyoder@...il.com, laurentiu.tudor@....com
Subject: Re: [PATCH 5/6] dma-mapping: support fsl-mc bus

On Mon, Mar 05, 2018 at 03:48:32PM +0000, Robin Murphy wrote:
> Unfortunately for us, fsl-mc is conceptually rather like PCI in that it's 
> software-discoverable and the only thing described in DT is the bus "host", 
> thus we need the same sort of thing as for PCI to map from the child 
> devices back to the bus root in order to find the appropriate firmware 
> node. Worse than PCI, though, we wouldn't even have the option of 
> describing child devices statically in firmware at all, since it's actually 
> one of these runtime-configurable "build your own network accelerator" 
> hardware pools where userspace gets to create and destroy "devices" as it 
> likes.

I really hate the PCI special case just as much.  Maybe we just
need a dma_configure method on the bus, and move PCI as well as fsl-mc
to it.