linux-kernel - Re: [PATCH v3 0/4] dma-mapping: introduce new dma unmap and sync variants

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Date:   Thu, 14 Nov 2019 11:13:28 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     David Miller <davem@...emloft.net>
CC:     "hch@....de" <hch@....de>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "joro@...tes.org" <joro@...tes.org>,
        Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Leo Li <leoyang.li@....com>,
        Diana Madalina Craciun <diana.craciun@....com>,
        Madalin Bucur <madalin.bucur@....com>,
        Camelia Alexandra Groza <camelia.groza@....com>,
        Roy Pledge <roy.pledge@....com>
Subject: Re: [PATCH v3 0/4] dma-mapping: introduce new dma unmap and sync
 variants

On 13.11.2019 22:11, David Miller wrote:
> From: Laurentiu Tudor <laurentiu.tudor@....com>
> Date: Wed, 13 Nov 2019 12:24:17 +0000
> 
>> From: Laurentiu Tudor <laurentiu.tudor@....com>
>>
>> This series introduces a few new dma unmap and sync api variants that,
>> on top of what the originals do, return the virtual address
>> corresponding to the input dma address. In order to do that a new dma
>> map op is added, .get_virt_addr that takes the input dma address and
>> returns the virtual address backing it up.
>> The second patch adds an implementation for this new dma map op in the
>> generic iommu dma glue code and wires it in.
>> The third patch updates the dpaa2-eth driver to use the new apis.
> 
> The driver should store the mapping in it's private software state if
> it needs this kind of conversion.

On this hardware there's no way of conveying additional frame 
information, such as original va/pa behind the dma address. We have also 
pondered on the idea of keeping this in some kind of data structure but 
could not find a lock-less solution which obviously would bring 
performance to the ground.
I'll let my colleagues maintaining these ethernet drivers to get into 
more details, if required.

---
Best Regards, Laurentiu