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Date:   Wed, 15 Jun 2022 16:46:03 +0200
From:   Frank Wunderlich <frank-w@public-files.de>
To:     Christoph Hellwig <hch@lst.de>, Robin Murphy <robin.murphy@arm.com>
CC:     linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
        Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: helping with remapping vmem for dma
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Am 15=2E Juni 2022 15:17:00 MESZ schrieb Christoph Hellwig <hch@lst=2Ede>:
>On Wed, Jun 15, 2022 at 02:15:33PM +0100, Robin Murphy wrote:
>> Put simply, if you want to call dma_map_single() on a buffer, then that=
=20
>> buffer needs to be allocated with kmalloc() (or technically alloc_pages=
(),=20
>> but then dma_map_page() would make more sense when dealing with entire=
=20
>> pages=2E
>
>Yes=2E  It sounds like the memory here comes from the dma coherent
>allocator, in which case the code need to use the address returned
>by that and not create another mapping=2E

As i have not found position where memory is allocated (this is a very hug=
e and dirty driver) is it maybe possible to check if buf is such "allready =
dma" memory (maybe is_vmalloc_addr) and call dma_single_map only if not (us=
ing original buf if yes)?

But i guess it should map only a part of available (pre-allocated) memory =
and other parts of this are used somewhere else=2E So i can ran into some i=
ssues caused by sharing this full block in different functions=2E
Hi,

Thanks for first suggestions=2E=20
regards Frank