linux-kernel - Re: [PATCH v2 1/3] dma-mapping: introduce new dma unmap and sync api variants

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Date:   Mon, 28 Oct 2019 13:38:05 +0100
From:   "hch@....de" <hch@....de>
To:     Laurentiu Tudor <laurentiu.tudor@....com>
Cc:     "hch@....de" <hch@....de>, "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>,
        "robin.murphy@....com" <robin.murphy@....com>,
        Diana Madalina Craciun <diana.craciun@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Madalin Bucur <madalin.bucur@....com>
Subject: Re: [PATCH v2 1/3] dma-mapping: introduce new dma unmap and sync
 api variants

On Thu, Oct 24, 2019 at 12:41:41PM +0000, Laurentiu Tudor wrote:
> From: Laurentiu Tudor <laurentiu.tudor@....com>
> 
> Introduce a few new dma unmap and sync variants that, on top of the
> original variants, return the virtual address corresponding to the
> input dma address.
> In order to implement this a new dma map op is added and used:
>     void *get_virt_addr(dev, dma_handle);
> It does the actual conversion of an input dma address to the output
> virtual address.

We'll definitively need an implementation for dma-direct at least as
well.  Also as said previously we need a dma_can_unmap_by_dma_addr()
or similar helper that tells the driver beforehand if this works, so
that the driver can either use a sub-optimal workaround or fail the
probe if this functionality isn't implemented.