linux-kernel - Re: About dma_sync_single_for

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Message-ID: <20120731083022.GA5026@ed-laptop>
Date:	Tue, 31 Jul 2012 10:30:22 +0200
From:	Karl Beldan <karl.beldan@...il.com>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: About dma_sync_single_for_{cpu,device}

On Tue, Jul 31, 2012 at 09:34:01AM +0200, Clemens Ladisch wrote:
> Karl Beldan wrote:
> > On 7/31/12, Clemens Ladisch <clemens@...isch.de> wrote:
> >> Karl Beldan wrote:
> >>> To tx a chunk of data from the SoC => network device, we :
> >>> - prepare a buffer with a leading header embedding a pattern,
> >>> - trigger the xfer and wait for an irq
> >>> // The device updates the pattern and then triggers an irq
> >>> - upon irq we check the pattern for the xfer completion
> >>>
> >>> I was expecting the following to work:
> >>> 	addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE);
> >>
> >> Of both the CPU and the device write to the buffer, you must use
> >> DMA_BIDIRECTIONAL.
> >
> > This does not work (tested) :  seems to me BIDIRECTIONAL would just
> > add invalidate, and invalidate before the ram has been updated, as
> > stated, does not work.
> 
> Please show the exact sequence of dma_* calls, and also show when and
> how the CPU and the device access the buffer.
> 
Hmm, so I just spotted a line where we peek in the buffer after
invalidating .. cannot believe I missed it .. so sorry for the noise ..
now it's working.
I felt I would find the culprit right after posting ;)
Thanks Clemens !
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