From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-path: Received: from mail-pg0-f65.google.com ([74.125.83.65]:37435 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753151AbdKVW2L (ORCPT ); Wed, 22 Nov 2017 17:28:11 -0500 Date: Wed, 22 Nov 2017 14:28:09 -0800 From: Guenter Roeck To: Robert Lippert Cc: linux-hwmon@vger.kernel.org, jdelvare@suse.com, linux-kernel@vger.kernel.org, xow@google.com, Robert Lippert Subject: Re: [PATCH] hwmon: (pmbus) Use 64bit math for DIRECT format values Message-ID: <20171122222809.GA2951@roeck-us.net> References: <20171122220843.18309-1-rlippert@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171122220843.18309-1-rlippert@google.com> Sender: linux-hwmon-owner@vger.kernel.org List-Id: linux-hwmon@vger.kernel.org On Wed, Nov 22, 2017 at 02:08:43PM -0800, Robert Lippert wrote: > Power values in the 100s of watt range can easily blow past > 32bit math limits when processing everything in microwatts. > > Use 64bit math instead to avoid these issues on common 32bit ARM > BMC platforms. > > Signed-off-by: Robert Lippert > --- > drivers/hwmon/pmbus/pmbus_core.c | 21 ++++++++++++--------- > 1 file changed, 12 insertions(+), 9 deletions(-) > > diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c > index 52a58b8b6e1b..f4efea9f282e 100644 > --- a/drivers/hwmon/pmbus/pmbus_core.c > +++ b/drivers/hwmon/pmbus/pmbus_core.c > @@ -499,8 +499,8 @@ static long pmbus_reg2data_linear(struct pmbus_data *data, > static long pmbus_reg2data_direct(struct pmbus_data *data, > struct pmbus_sensor *sensor) > { > - long val = (s16) sensor->data; > - long m, b, R; > + s64 val = (s16) sensor->data; > + s64 m, b, R; > > m = data->info->m[sensor->class]; > b = data->info->b[sensor->class]; > @@ -528,11 +528,13 @@ static long pmbus_reg2data_direct(struct pmbus_data *data, > R--; > } > while (R < 0) { > - val = DIV_ROUND_CLOSEST(val, 10); > + do_div(val, 10); Any reason to not use DIV_ROUND_CLOSEST_ULL ? > R++; > } > > - return (val - b) / m; > + val = val - b; > + do_div(val, m); > + return val; Can this overflow ? > } > > /* > @@ -656,7 +658,8 @@ static u16 pmbus_data2reg_linear(struct pmbus_data *data, > static u16 pmbus_data2reg_direct(struct pmbus_data *data, > struct pmbus_sensor *sensor, long val) > { > - long m, b, R; > + s64 m, b, R; > + s64 val64 = val; > > m = data->info->m[sensor->class]; > b = data->info->b[sensor->class]; > @@ -673,18 +676,18 @@ static u16 pmbus_data2reg_direct(struct pmbus_data *data, > R -= 3; /* Adjust R and b for data in milli-units */ > b *= 1000; > } > - val = val * m + b; > + val64 = val64 * m + b; > > while (R > 0) { > - val *= 10; > + val64 *= 10; > R--; > } > while (R < 0) { > - val = DIV_ROUND_CLOSEST(val, 10); > + do_div(val64, 10); Same here. > R++; > } > > - return val; > + return (u16) val64; Can this overflow ? > } > > static u16 pmbus_data2reg_vid(struct pmbus_data *data, > -- > 2.15.0.448.gf294e3d99a-goog >