linux-kernel - Re: About dma_sync_single_for

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Message-ID: <50178A69.8050906@ladisch.de>
Date:	Tue, 31 Jul 2012 09:34:01 +0200
From:	Clemens Ladisch <clemens@...isch.de>
To:	Karl Beldan <karl.beldan@...il.com>
CC:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: About dma_sync_single_for_{cpu,device}

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.


Regards,
Clemens
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