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

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Date:   Fri, 9 Mar 2018 18:29:41 +0000
From:   Nipun Gupta <nipun.gupta@....com>
To:     Christoph Hellwig <hch@....de>
CC:     Robin Murphy <robin.murphy@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "joro@...tes.org" <joro@...tes.org>, Leo Li <leoyang.li@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Bharat Bhushan <bharat.bhushan@....com>,
        "stuyoder@...il.com" <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>
Subject: RE: [PATCH 5/6] dma-mapping: support fsl-mc bus



> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@....de]
> Sent: Thursday, March 08, 2018 13:11
> 
> On Tue, Mar 06, 2018 at 04:41:56AM +0000, Nipun Gupta wrote:
> > Sorry for asking a trivial question - looking into dma_configure() I see that
> > PCI is used in the start and the end of the API.
> > In the end part pci_put_host_bridge_device() is called.
> > So are two bus callbacks something like 'dma_config_start' &
> 'dma_config_end'
> > will be required where the former one will return "dma_dev"?
> 
> I'd just use dma_configure as the callback.

This would be a decent stuff.

> 
> Currently the of_dma_configure and acpi_dma_configure are only used
> for PCI anyway, as no one else sets a non-NULL dma dev.

My understanding is that even the platform bus uses the of_dma_configure
and probably acpi_dma_configure too. So platform bus may also need the
callback implemented. Please correct me if my understanding is wrong.

I will submit the patch with 'dma_configure' callback implemented for
the busses shortly.

> For fsl-mc I suspect only of_dma_configure is relevanet, so just call that directly.
> If at some point we get enough busses with either OF or ACPI we could
> create a helper called from ->dma_configure for that.

Totally agree with this.

Thanks,
Nipun