linux-kernel - Re: [PATCH v2 2/2] hwrng: iproc-rng200

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Message-ID: <2555599.AxGoQ20pkj@wuerfel>
Date:	Sat, 28 Feb 2015 20:31:27 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Scott Branden <sbranden@...adcom.com>
Cc:	bcm-kernel-feedback-list@...adcom.com,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Matt Mackall <mpm@...enic.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Grant Likely <grant.likely@...aro.org>,
	Ray Jui <rjui@...adcom.com>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazao <anatol@...gle.com>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] hwrng: iproc-rng200 - Add Broadcom IPROC RNG driver

On Saturday 28 February 2015 08:01:11 Scott Branden wrote:
> > The udelay(10) that the other drivers have seems about appropriate then,
> > and we can independently think of a way to refine the interface.
> > Please add a comment that explains the rate. Also, is there some kind
> > of FIFO present in the hwrng device? If it can store close to 1ms work
> > of data (1000 bits), you can just use an msleep(1) to wait for the
> > pool to recover.
> FIFO is 512 bits.  I will look as to whether we can live with 1/2 
> throughput.

In that case, I think usleep_range(min(len * 8, 500), 500)) would be
a good compromise: it waits at most until the fifo is full, but might
return earlier if enough bits are available to fulfill the request.

	Arnd
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