linux-kernel - Re: [PATCH v2 2/2] Crypto: Talitos: Support for Async

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Date:	Fri, 18 Dec 2009 15:17:42 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Li Yang-R58472 <r58472@...escale.com>
Cc:	"Ira W. Snyder" <iws@...o.caltech.edu>,
	Kumar Gala <galak@...nel.crashing.org>,
	herbert@...dor.apana.org.au,
	Tabi Timur-B04825 <B04825@...escale.com>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	linuxppc-dev@...abs.org,
	Suresh Vishnu-B05022 <B05022@...escale.com>,
	linux-crypto@...r.kernel.org,
	Dudhat Dipen-B09055 <B09055@...escale.com>,
	Gupta Maneesh-B18878 <B18878@...escale.com>
Subject: Re: [PATCH v2 2/2] Crypto: Talitos: Support for Async_tx XOR offload

On Fri, Dec 18, 2009 at 8:02 AM, Li Yang-R58472 <r58472@...escale.com> wrote:
>
>>Subject: Re: [PATCH v2 2/2] Crypto: Talitos: Support for
>>Async_tx XOR offload
>>
>>Ira W. Snyder wrote:
>>> Yes, I have used the device_prep_dma_interrupt()
>>functionality quite a
>>> while back. However, I found it to be pretty much useless.
>>
>>The specific case it is needed for Talitos/raid is a channel
>>switch interrupt.  The interrupt causes the cleanup operation
>>to be run which will kick off any pending dependent operations
>>on the xor channel.  In the raid case we only have callbacks
>>at the end of a chain, so we need the interrupt to kick the
>>engine in an operation chain like
>>xor->copy->xor->callback.
>
> I am wondering if can use more callbacks to kick off pending dependent operations?
> Like xor->callback->copy->callback->xor->callback?
>

No, the callback field is reserved for clients of the api.  What you want is:

xor->cleanupT->copy->cleanupF->xor->cleanupT->callback

Where cleanupT is the Talitos descriptor cleanup routine and cleanupF
is from fsldma.  The assumption is that the interrupt kicks the
cleanup routine and that calls dma_run_dependencies().

--
Dan
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