linux-kernel - Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

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Date:	Tue, 18 Oct 2011 13:56:24 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	Russell King <rmk@....linux.org.uk>,
	"Bounine, Alexandre" <Alexandre.Bounine@....com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	Barry Song <21cnbao@...il.com>, linux-kernel@...r.kernel.org,
	DL-SHA-WorkGroupLinux <workgroup.linux@....com>,
	Dave Jiang <dave.jiang@...el.com>
Subject: Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

On Tue, 2011-10-18 at 14:00 +0530, Jassi Brar wrote:
> On 18 October 2011 13:12, Russell King <rmk@....linux.org.uk> wrote:
> > On Tue, Oct 18, 2011 at 11:15:29AM +0530, Jassi Brar wrote:
> >> On 18 October 2011 02:37, Bounine, Alexandre <Alexandre.Bounine@....com> wrote:
> >> > With item #1 above being a separate topic, I may have a problem with #2
> >> > as well: dma_addr_t is sized for the local platform and not guaranteed
> >> > to be a 64-bit value (which may be required by a target).
> >> > Agree with #3 (if #1 and #2 work).
> >> >
> >> Perhaps simply change dma_addr_t to u64 in dmaengine.h alone ?
> >
> > That's just an idiotic suggestion - there's no other way to put that.
> > Let's have some sanity here.
> >
> Yeah, I am not proud of the workaround, so I only probed the option.
> I think I need to explain myself.
> 
> The case here is that even a 32-bit RapidIO host could ask transfer against
> 64-bit address space on a remote device. And vice versa 64->32.
I thought RIO address were always 64 + 2 bits, irrespective of what the
host system is...

> 
> > dma_addr_t is the size of a DMA address for the CPU architecture being
> > built.  This has no relationship to what any particular DMA engine uses.
> >
> Yes, so far the dmaengine ever only needed to transfer within platform's
> address-space. So the assumption that src and dst addresses could
> be contained within dma_addr_t, worked.
> If the damengine is to get rid of that assumption/constraint, the memcpy,
> slave_sg etc need to accept addresses specified in bigger of the host and
> remote address space, and u64 is the safe option.
> Ultimately dma_addr_t is either u32 or u64.
> 
> If you still think that's unacceptable, please do show us the optimal
> path forward.


-- 
~Vinod

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