From patchwork Thu Sep 8 15:24:32 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Farber, Eliav" X-Patchwork-Id: 12970271 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04CA7C54EE9 for ; Thu, 8 Sep 2022 15:30:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229637AbiIHPat (ORCPT ); Thu, 8 Sep 2022 11:30:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231549AbiIHPaV (ORCPT ); Thu, 8 Sep 2022 11:30:21 -0400 Received: from smtp-fw-9102.amazon.com (smtp-fw-9102.amazon.com [207.171.184.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E0176350; Thu, 8 Sep 2022 08:29:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1662650972; x=1694186972; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=dupzsTIu8ztsHP46WQosJM2o1HjY7SxoxCnga0WjaRI=; b=hYB7VSgPUrzn3/c/f+SQmESzGFPWJTmgLiUwkXSPNnIWUIs2C9K9czwq oAudOcSyCphAogCX4CZ19cG7MXnVTcBePLzwsSzDzSYLnqiEuuBXOa8cI TdsryyMI4bvZI++XDD0rnwd3ByHXuUrcFFi+3B+X0xtHqG8IoTwTpDO9V c=; X-IronPort-AV: E=Sophos;i="5.93,300,1654560000"; d="scan'208";a="257507790" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO email-inbound-relay-iad-1d-10222bbc.us-east-1.amazon.com) ([10.25.36.210]) by smtp-border-fw-9102.sea19.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Sep 2022 15:25:13 +0000 Received: from EX13MTAUWB001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1d-10222bbc.us-east-1.amazon.com (Postfix) with ESMTPS id D37831A08F1; Thu, 8 Sep 2022 15:25:09 +0000 (UTC) Received: from EX19D013UWB003.ant.amazon.com (10.13.138.111) by EX13MTAUWB001.ant.amazon.com (10.43.161.207) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Thu, 8 Sep 2022 15:24:53 +0000 Received: from EX13MTAUEA001.ant.amazon.com (10.43.61.82) by EX19D013UWB003.ant.amazon.com (10.13.138.111) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1118.12; Thu, 8 Sep 2022 15:24:52 +0000 Received: from dev-dsk-farbere-1a-46ecabed.eu-west-1.amazon.com (172.19.116.181) by mail-relay.amazon.com (10.43.61.243) with Microsoft SMTP Server id 15.0.1497.38 via Frontend Transport; Thu, 8 Sep 2022 15:24:51 +0000 Received: by dev-dsk-farbere-1a-46ecabed.eu-west-1.amazon.com (Postfix, from userid 14301484) id 7EFBC4D80; Thu, 8 Sep 2022 15:24:49 +0000 (UTC) From: Eliav Farber To: , , , , , , , , CC: , , , "Andy Shevchenko" Subject: [PATCH v5 04/21] hwmon: (mr75203) fix voltage equation for negative source input Date: Thu, 8 Sep 2022 15:24:32 +0000 Message-ID: <20220908152449.35457-5-farbere@amazon.com> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20220908152449.35457-1-farbere@amazon.com> References: <20220908152449.35457-1-farbere@amazon.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org According to Moortec Embedded Voltage Monitor (MEVM) series 3 data sheet, the minimum input signal is -100mv and maximum input signal is +1000mv. The equation used to convert the digital word to voltage uses mixed types (*val signed and n unsigned), and on 64 bit machines also has different size, since sizeof(u32) = 4 and sizeof(long) = 8. So when measuring a negative input, n will be small enough, such that PVT_N_CONST * n < PVT_R_CONST, and the result of (PVT_N_CONST * n - PVT_R_CONST) will overflow to a very big positive 32 bit number. Then when storing the result in *val it will be the same value just in 64 bit (instead of it representing a negative number which will what happen when sizeof(long) = 4). When -1023 <= (PVT_N_CONST * n - PVT_R_CONST) <= -1 dividing the number by 1024 should result of in 0, but because ">> 10" is used, and the sign bit is used to fill the vacated bit positions, it results in -1 (0xf...fffff) which is wrong. This change fixes the sign problem and supports negative values by casting n to long and replacing the shift right with div operation. Fixes: 9d823351a337 ("hwmon: Add hardware monitoring driver for Moortec MR75203 PVT controller") Signed-off-by: Eliav Farber Reviewed-by: Andy Shevchenko --- V5 -> V4: - Add detailed comment in code explaining the cast and the div instead of right shift or use of BIT(). V4 -> V3: - Remove unrelated change (add of empty line). V3 -> V2: - Fix equation to support negative values instead of limiting value to zero. drivers/hwmon/mr75203.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/drivers/hwmon/mr75203.c b/drivers/hwmon/mr75203.c index 62df0c9498f3..8211d463495d 100644 --- a/drivers/hwmon/mr75203.c +++ b/drivers/hwmon/mr75203.c @@ -201,8 +201,18 @@ static int pvt_read_in(struct device *dev, u32 attr, int channel, long *val) return ret; n &= SAMPLE_DATA_MSK; - /* Convert the N bitstream count into voltage */ - *val = (PVT_N_CONST * n - PVT_R_CONST) >> PVT_CONV_BITS; + /* + * Convert the N bitstream count into voltage. + * To support negative voltage calculation for 64bit machines + * n must be cast to long, since n and *val differ both in + * signedness and in size. + * Division is used instead of right shift, because for signed + * numbers, the sign bit is used to fill the vacated bit + * positions, and if the number is negative, 1 is used. + * BIT(x) may not be used instead of (1 << x) because it's + * unsigned. + */ + *val = (PVT_N_CONST * (long)n - PVT_R_CONST) / (1 << PVT_CONV_BITS); return 0; default: