linux-kernel - Re: [RFC PATCH v2 1/9] crypto: qce: Add core driver implementation

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Message-ID: <536BFDD3.9090609@mm-sol.com>
Date:	Fri, 09 May 2014 00:57:39 +0300
From:	Stanimir Vabanov <svarbanov@...sol.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	"David S. Miller" <davem@...emloft.net>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	linux-arm-msm@...r.kernel.org,
	Mona Hossain <mhossain@...eaurora.org>,
	Hariprasad Dhalinarasimha <hnamgund@...eaurora.org>,
	Zhen Kong <zkong@...eaurora.org>,
	Niranjana Vishwanathapura <nvishwan@...eaurora.org>,
	Rohit Vaswani <rvaswani@...eaurora.org>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [RFC PATCH v2 1/9] crypto: qce: Add core driver implementation

Hi Herbert,

On 04/28/2014 11:59 AM, Herbert Xu wrote:
> On Mon, Apr 14, 2014 at 03:48:37PM +0300, Stanimir Varbanov wrote:
>>
>> +#define QCE_MAJOR_VERSION5	0x05
>> +#define QCE_QUEUE_LENGTH	50
> 
> What is the purpose of this software queue? Why can't you directly
> feed the requests to the hardware?
> 
> If the hardware can't handle more than 50 requests in-flight,
> then your software queue has failed to handle this since you're
> taking requests off the queue before you touch the hardware so
> you're not really limiting it to 50.  That is, for users that
> can wait you're potentially dropping their requests instead
> of letting them wait through the backlog mechanism.

My assumption was that crypto_ablkcipher_encrypt/decrypt couldn't sleep
and I should take the request almost immediately and return the
appropriate error value - EINPROGRESS if the hardware is idle and EBUSY
if the hardware working on some previous request. Thus if the returned
error is EBUSY and the request could be backlogged I should call
backlog->complete() when this request is taken actually for processing.

What I've done in practice is another story.

Is that assumption correct? If so, is crypto_enqueue|dequeue_request()
are the proper tools to implement this behaviour?

regards,
Stan
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