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

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Message-ID: <579b3df0-f78b-3c77-7a8a-9cd69848f1af@arm.com>
Date:   Fri, 9 Mar 2018 18:50:05 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Nipun Gupta <nipun.gupta@....com>, Christoph Hellwig <hch@....de>
Cc:     "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

On 09/03/18 18:29, Nipun Gupta wrote:
> 
> 
>> -----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.

Yes, the PCI version should end up looking a lot like the old 
pci_dma_configure() used to, before everything got pulled together.

>> 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.

Indeed, platform and AMBA will want an implementation to dispatch 
between {of,acpi}_dma_configre() per the current logic. Host1x doesn't 
seem to care about ACPI so probably wants its own just calling 
of_dma_configure().

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

Cheers - I've been trying to find some time to take a look myself, but 
having something to review instead would certainly be easier :)

Robin.