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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 28 Feb 2015 08:01:11 -0800
From:	Scott Branden <sbranden@...adcom.com>
To:	Arnd Bergmann <arnd@...db.de>
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 15-02-27 01:14 AM, Arnd Bergmann wrote:
> On Thursday 26 February 2015 14:26:02 Scott Branden wrote:
>> On 15-02-26 12:15 PM, Arnd Bergmann wrote:
>>>> On 15-02-25 11:17 AM, Arnd Bergmann wrote:
>>>>> On Wednesday 25 February 2015 10:16:24 Scott Branden wrote:
>>>> This code was following examples of other open source drivers - bcm2835
>>>> and exynos both use cpu_relax.  I'll have to look into this more to
>>>> understand.
>>>>
>>>
>>> The majority of the driver apparently use udelay(10) to wait, which is
>>> not much better but at least consistent. The cpu_relax() call probably
>>> gives better throughput.
>>>
>>> I don't understand why none of the drivers actually attempts to
>>> msleep(), but that may be because the delay is much too long.
>>>
>>> Can you find out what the expected latency is for new data to
>>> become available on your hardware?
>> RNG generates at a nominal 1 Mbps.  So to generate 32 bits of data takes
>> approximately 32 us.
>
> 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.
>
> Another option would be to use usleep_range() with the exact amount
> of time to wait for, the lower bound being the minimum number of
> bytes asked for and the fifo size, the upper bound being the fifo
> size.
>
> 	Arnd
>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/