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

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Message-ID: <5361265D.2000706@mm-sol.com>
Date:	Wed, 30 Apr 2014 19:35:41 +0300
From:	Stanimir Varbanov <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?

Good question. This is a leftover from original driver.

The hardware can handle one request at a time. After you raise the
question I think the queue length should be 1 or remove it completely. I
don't know why the original codeaurora's driver use 50.

> 
> 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.

-- 
regards,
Stan
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