Re: UBIFS with dma on 4.6 kernel is not working

From	Richard Weinberger <richard@nod.at>
Newsgroups	linux.kernel
Subject	Re: UBIFS with dma on 4.6 kernel is not working
Date	2016-10-24 09:10 +0200
Message-ID	<svHyp-4js-19@gated-at.bofh.it> (permalink)
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Christoph,

On 21.10.2016 15:15, Christoph Hellwig wrote:
> On Fri, Oct 21, 2016 at 03:07:57PM +0200, Richard Weinberger wrote:
>> Hmm, thought this is still problematic on VIVT architectures.
>> Boris tried to provide a solution for that some time ago:
>> http://www.spinics.net/lists/arm-kernel/msg494025.html
> 
> Things have been working fine for approx 10 years when using
> flush_kernel_vmap_range before doing I/O using the physical addresses and
> then invalidate_kernel_vmap_range when completing the I/O and going back
> to using the virtual mapping for XFS.
> 
> Of course all this assumes at least the higher level that did the
> vm_map_ram operation knows about this dance between virtually mapped and
> physiscal addresses. 

Good to know, I was clearly wrong.

Let's see whether the costs of flush_kernel_vmap_range and invalidate_kernel_vmap_range
are smaller than the speedup by DMA on embedded platforms.
We'll have to test it.

Thanks,
//richard

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Re: UBIFS with dma on 4.6 kernel is not working Richard Weinberger <richard@nod.at> - 2016-10-21 11:30 +0200
  Re: UBIFS with dma on 4.6 kernel is not working Cyrille Pitchen <cyrille.pitchen@atmel.com> - 2016-10-21 14:00 +0200
  Re: UBIFS with dma on 4.6 kernel is not working Christoph Hellwig <hch@infradead.org> - 2016-10-21 15:00 +0200
    Re: UBIFS with dma on 4.6 kernel is not working Richard Weinberger <richard@nod.at> - 2016-10-21 15:10 +0200
      Re: UBIFS with dma on 4.6 kernel is not working Christoph Hellwig <hch@infradead.org> - 2016-10-21 15:20 +0200
        Re: UBIFS with dma on 4.6 kernel is not working Richard Weinberger <richard@nod.at> - 2016-10-24 09:10 +0200

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