From mboxrd@z Thu Jan 1 00:00:00 1970 From: Scott Branden Subject: Re: [PATCH v2 2/2] hwrng: iproc-rng200 - Add Broadcom IPROC RNG driver Date: Thu, 26 Feb 2015 11:37:20 -0800 Message-ID: <54EF75F0.7000901@broadcom.com> References: <1424888184-22180-3-git-send-email-sbranden@broadcom.com> <3062825.7b1oYP4yuL@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <3062825.7b1oYP4yuL@wuerfel> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Arnd Bergmann Cc: bcm-kernel-feedback-list-dY08KVG/lbpWk0Htik3J/w@public.gmane.org, Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Matt Mackall , Herbert Xu , Grant Likely , Ray Jui , Jonathan Richardson , Dmitry Torokhov , Anatol Pomazao , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: devicetree@vger.kernel.org Response inline. On 15-02-25 11:17 AM, Arnd Bergmann wrote: > On Wednesday 25 February 2015 10:16:24 Scott Branden wrote: >> This adds a driver for random number generator present on Broadcom >> IPROC devices. >> >> Reviewed-by: Ray Jui >> Signed-off-by: Scott Branden > > The driver looks reasonable overall, I have just one question about > something that sticks out: > >> + while ((num_remaining > 0) && time_before(jiffies, idle_endtime)) { > ... >> + >> + /* Are there any random numbers available? */ >> + if ((ioread32(rng_base + RNG_FIFO_COUNT_OFFSET) & >> + RNG_FIFO_COUNT_RNG_FIFO_COUNT_MASK) > 0) { > ... >> + } else { >> + if (!wait) >> + /* Cannot wait, return immediately */ >> + return max - num_remaining; >> + >> + /* Can wait, give others chance to run */ >> + cpu_relax(); >> + } >> + } >> + > > It looks like you do a busy-loop around cpu_relax here if asked to wait. > Is this intentional? I would normally expect either cond_resched() or > some msleep() instead. 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. > > Arnd > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html