linux-kernel - Re: [RESEND2 PATCH 0/3] Fix kernel panic in dma-coherent

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Date:	Mon, 8 Feb 2016 17:50:55 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Brian Starkey <brian.starkey@....com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org,
	Michal Nazarewicz <mina86@...a86.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RESEND2 PATCH 0/3] Fix kernel panic in dma-coherent

On Mon, Feb 08, 2016 at 05:30:49PM +0000, Brian Starkey wrote:
> Hi,
> 
> I'm resending these again to try and garner some interest. Without
> this series, dma-coherent cannot be used on arm64 platforms.

I think you need to characterize that a bit better. I see plenty of
instances of 'dma-coherent' in dts files, assuming you mean the DT
dma-coehrent property.

If not, feel free to stop reading now.

Currently dma-coherent isn't well-defined, but it's de-facto semantics
are that a device makes accesses which are coherent with data accesses
made by CPUs with Normal, Inner Shareable, Inner Write-Back Cacheable,
Outer Write-Back Cacheable attributes.

> The decision to add MEMREMAP_WC came out of a previous discussion with
> Dan Williams and Catalin Marinas about the same problem[1].

As pgprot_writecombine is Normal Non-Cacheable, this is a completely
different idea of coherency to that described by the DT dma-coherent
property.

We should not overload that to mean different things.

Thanks,
Mark.

> These patches implement a MEMREMAP_WC flag for memremap(), which can
> be used to obtain writecombine mappings. This is then used for setting
> up dma_coherent_mem regions which use the DMA_MEMORY_MAP flag.
> They apply cleanly on 4.5-rc3.
> 
> Patch 3 makes sure that the appropriate memset function is used
> when zeroing coherent allocations, which fixes an alignment fault on
> arm64.
> 
> Best Regards,
> Brian
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-December/390857.html
> 
> Brian Starkey (3):
>   memremap: add MEMREMAP_WC flag
>   drivers: dma-coherent: use MEMREMAP_WC for DMA_MEMORY_MAP
>   drivers: dma-coherent: use memset_io for DMA_MEMORY_IO
> 
>  drivers/base/dma-coherent.c |   25 ++++++++++++++++++++-----
>  include/linux/io.h          |    1 +
>  kernel/memremap.c           |   15 +++++++++++++--
>  3 files changed, 34 insertions(+), 7 deletions(-)
> 
> -- 
> 1.7.9.5
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

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