linux-kernel - Re: [PATCH 15/16] dmaengine: add transfered member to dma_async_tx

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Date:	Thu, 25 Jul 2013 17:32:35 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	balbi@...com, george.cherian@...com,
	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>
Subject: Re: [PATCH 15/16] dmaengine: add transfered member to dma_async_tx_descriptor

On 07/25/2013 05:12 PM, Sebastian Andrzej Siewior wrote:
> On 07/25/2013 04:57 PM, Lars-Peter Clausen wrote:
>> I'm not sure that this will work. Once you've submitted the descriptor it is
>> owned by the dmaengine driver and you are not allowed to dereference it
>> anymore since the dmaengine driver might free the memory at any time. You
>> should only reference the descriptor by the cookie returned by submit().
> 
> I see. But it can't be reused before calling the callback if it is
> going to call the callback, right?
> So if this is a no-no, I'm left with an additional argument to the
> complete callback?

Hm, maybe using dmaengine_tx_status() and checking the residue field of the
state struct. transferred is basically len - residue.

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