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

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Message-ID: <20091217170958.GE18271@ovro.caltech.edu>
Date:	Thu, 17 Dec 2009 09:09:58 -0800
From:	"Ira W. Snyder" <iws@...o.caltech.edu>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Kumar Gala <galak@...nel.crashing.org>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"B04825@...escale.com" <B04825@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"linuxppc-dev@...abs.org" <linuxppc-dev@...abs.org>,
	Vishnu Suresh <Vishnu@...escale.com>,
	"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
	Dipen Dudhat <Dipen.Dudhat@...escale.com>,
	Maneesh Gupta <Maneesh.Gupta@...escale.com>,
	"R58472@...escale.com" <R58472@...escale.com>
Subject: Re: [PATCH v2 2/2] Crypto: Talitos: Support for Async_tx XOR
 offload

On Wed, Dec 16, 2009 at 03:47:48PM -0700, Dan Williams wrote:
> Kumar Gala wrote:
> >>> Changes with respect to v1 as per comments received
> >>> o. Rebased to linux-next as of 20091216
> >>> o. The selection is based exclusive of fsldma
> >>> o. Intoduced a new Kernel Configuration variable
> >>>   *. This enables selecting the Cryptographic functionality
> >>>      of Talitos along with fsldma.
> >>>   *. Disables the XOR parity calculation offload, if fsldma enabled
> >>>      either as kernel in-built or as a module
> >>>   *. Once the inter-operability with fsldma is resolved, this option
> >>>      can be removed
> >> wait, why can't the interoperability bug be fixed in the first place?
> > 
> > I agree w/Kim.  We need to better understand what the bug is and how to reproduce it so we can get to the root cause.
> > 
> > Paper taping over it by disabling fsldma is not the right solution.
> 
> Hopefully this prompts fsldma authors to get involved because the 
> interoperability issue has been out there without comment*, just 
> band-aids, since October.
> 
> --
> Dan
> 
> * well one comment from Ira saying the interrupt functionality worked 
> for him.

Yes, I have used the device_prep_dma_interrupt() functionality quite a
while back. However, I found it to be pretty much useless. Any
functionality I need is covered by adding a callback to the last DMA
memcpy() operation. Since the operations happen in-order, I can be sure
that the entire set of memcpy()s cas completed. I never needed the
capability to generate an interrupt without a memcpy().

I agree that the fsldma driver could use some love. There are places
where I am still not confident in the locking. Perhaps I can find some
time over Christmas to work on it, but I need someone with 85xx/86xx
hardware to test the changes. I only have 83xx hardware.

Ira
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