Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762498Ab3DCRGT (ORCPT ); Wed, 3 Apr 2013 13:06:19 -0400 Received: from mail-la0-f47.google.com ([209.85.215.47]:33049 "EHLO mail-la0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760213Ab3DCRGQ (ORCPT ); Wed, 3 Apr 2013 13:06:16 -0400 MIME-Version: 1.0 In-Reply-To: <5144849A.8050907@metafoo.de> References: <1363364801-23684-1-git-send-email-ch.naveen@samsung.com> <51439846.9090201@metafoo.de> <5144849A.8050907@metafoo.de> Date: Wed, 3 Apr 2013 10:06:14 -0700 X-Google-Sender-Auth: yHxoJXnYms1MdD_Xvt_zEREJtYI Message-ID: Subject: Re: [RFC: PATCH 2/2] iio: adc: exynos_adc: Handle timeout and race conditions From: Doug Anderson To: Lars-Peter Clausen Cc: Naveen Krishna Chatradhi , linux-iio , "linux-kernel@vger.kernel.org" , linux-samsung-soc@vger.kernel.org, Greg Kroah-Hartman , Naveen Krishna Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2276 Lines: 53 Lars, On Sat, Mar 16, 2013 at 7:41 AM, Lars-Peter Clausen wrote: > I think you still need the mutex for serialization, otherwise the requests > would just cancel each other out. Btw. what happens if you start a conversion > while another is still in progress? Is it possible to abort a conversion? I was thinking that the spinlock would just replace the mutex for the purposes of serialization. I stepped back a bit, though, and I'm wondering if we're over-thinking things. The timeout case should certainly be handled properly (thanks for pointing it out), but getting a timeout is really not expected and adding a lot of extra overhead to handle it elegantly seems a bit much? Specifically, the mutex means that we have one user of the ADC at a time, and ADC conversion has nothing variable about it. The user manual that I have access to talks about 12-bit conversion happening in 1 microsecond with a 5MHz input clock or 5 microseconds with a 1MHz input clock. Even if someone has clocks configured very differently, it would be hard to imagine a conversion actually taking a full second. ...so that means that if the timeout actually fires then something else fairly drastic has gone wrong. It's _very_ unlikely that the IRQ will still go off for this conversion sometime in the future. To me, total modifications to what's landed already ought to be: * Change timeout to long (from unsigned long) * Make sure we return errors (negative results) from wait_for_completion_interruptible_timeout() properly. * If we get back a value of 0 from wait_for_completion_interruptible_timeout() then we should print a warning and attempt machinations to reset the ADC. Without ever seeing real-world situtations that would cause a real timeout these machinations would be a bit of a guess (is resetting the adc useful when it's more likely that someone accidentally messed with the clock tree or power gated the ADC?)... ...or perhaps a warning and a TODO in the code would be enough? Thoughts? -Doug -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/