From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:46372 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750960AbeBQMil (ORCPT ); Sat, 17 Feb 2018 07:38:41 -0500 Date: Sat, 17 Feb 2018 12:38:36 +0000 From: Jonathan Cameron To: "Gustavo A. R. Silva" Cc: Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, Marc Titinger , Stefan =?UTF-8?B?QnLDvG5z?= Subject: Re: [PATCH] iio: adc: ina2xx: Use 64-bit arithmetic instead of 32-bit Message-ID: <20180217123836.61cb3b25@archlinux> In-Reply-To: <20180213165258.GA12967@embeddedor.com> References: <20180213165258.GA12967@embeddedor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On Tue, 13 Feb 2018 10:52:58 -0600 "Gustavo A. R. Silva" wrote: > Add suffix ULL to constant 1000 in order to give the compiler complete > information about the proper arithmetic to use. Notice that this > constant is used in a context that expects an expression of type > u64 (64 bits, unsigned). > > The expression 1000 * sampling_us is currently being evaluated > using 32-bit arithmetic. > > Addresses-Coverity-ID: 1463793 > Signed-off-by: Gustavo A. R. Silva I've been trying to figure out if this matters in reality. i.e. whether or not sampling_us is big enough for us to need 64 bit multiplication. It's equal to the output for the macro SAMPLING_PERIOD(c) (int_time_vbus + int_time_vshunt) * avg So taking max values (8244 + 68100) * 1024 = 78176256 Then * 1000 which brings it well into the > 32bit range. So the next question is when was this introduced. I guess it was Stefan's recent patch but haven't checked yet... Marc / Stephan, could you check if we are correct in thinking this is a real bug rather than just a numerical oddity? Thanks, Jonathan > --- > drivers/iio/adc/ina2xx-adc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c > index 0635a79..8649700 100644 > --- a/drivers/iio/adc/ina2xx-adc.c > +++ b/drivers/iio/adc/ina2xx-adc.c > @@ -810,7 +810,7 @@ static int ina2xx_capture_thread(void *data) > * multiple times, i.e. samples are dropped. > */ > do { > - timespec64_add_ns(&next, 1000 * sampling_us); > + timespec64_add_ns(&next, 1000ULL * sampling_us); > delta = timespec64_sub(next, now); > delay_us = div_s64(timespec64_to_ns(&delta), 1000); > } while (delay_us <= 0);