linux-kernel - Re: [PATCH v2] staging: ion: Add a default struct device for cma heap

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Message-ID: <20150807155004.GA22612@shbuild888>
Date:	Fri, 7 Aug 2015 23:50:04 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	John Stultz <john.stultz@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] staging: ion: Add a default struct device for cma heap

On Fri, Aug 07, 2015 at 04:48:28PM +0200, Michal Nazarewicz wrote:
> On Fri, Aug 07 2015, Feng Tang wrote:
> > As I described above, the dummy struct device is only needed for
> > dma request, its lifetime is align with the cma_heap itself. 
> 
> Again, this is from perspective of someone who is unfamiliar with ION,
> but perhaps a viable solution is to bypass DMA API and just call
> cma_alloc directly?

For ion cma heap, the buffer allocation func ion_cma_allocate() will
call dma_alloc_coherent(dev, ...). And dma_alloc_coherent() is
implemented by each architeture(arm/m68k/x86 etc), and many Arch's
implementation doesn't use cma, but use alloc_pages() like APIs.
So I'm afraid we can't direcly call cma_alloc directly here.

Thanks,
Feng
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