From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934856AbeB1Uzt (ORCPT ); Wed, 28 Feb 2018 15:55:49 -0500 Received: from mail.kernel.org ([198.145.29.99]:39618 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934739AbeB1Uzr (ORCPT ); Wed, 28 Feb 2018 15:55:47 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 10D43214EE Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=helgaas@kernel.org Date: Wed, 28 Feb 2018 14:55:46 -0600 From: Bjorn Helgaas To: "Gustavo A. R. Silva" Cc: Andy Shevchenko , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] PCI/ASPM: Change type of threshold_ns variable to u32 Message-ID: <20180228205546.GL127842@bhelgaas-glaptop.roam.corp.google.com> References: <20180227231952.GA9001@embeddedor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180227231952.GA9001@embeddedor.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 27, 2018 at 05:19:52PM -0600, Gustavo A. R. Silva wrote: > It seems that the expression threshold_us * 1000 will never exceed the > 32-bit limits [1]. So changing the type of threshold_ns from u64 to u32 > seems sensible [2]. > > [1] https://marc.info/?l=linux-kernel&m=151855021100725&w=2 > [2] https://marc.info/?l=linux-kernel&m=151976318924615&w=2 > > Addresses-Coverity-ID: 1462501 > Signed-off-by: Gustavo A. R. Silva Applied with Andy's Reviewed-by to pci/aspm for v4.17, thanks! I included a more detailed analysis in the changelog: PCI/ASPM: Declare threshold_ns as u32, not u64 aspm_calc_l1ss_info() computes l1_2_threshold in microseconds as: l1_2_threshold = 2 + 4 + t_common_mode + t_power_on; where t_common_mode is at most 255us: PCI_L1SS_CAP_CM_RESTORE_TIME 0x0000ff00 <-- 8 bits; <256us and t_power_on is at most 31 * 100us = 3100us: PCI_L1SS_CAP_P_PWR_ON_VALUE 0x00f80000 <-- 5 bits; <32 PCI_L1SS_CAP_P_PWR_ON_SCALE 0x00030000 <-- *2us, *10us, or *100us So l1_2_threshold is at most 2 + 4 + 255 + 3100 = 3361, which means threshold_ns is at most 3361 * 1000 = 3361000, which easily fits in a u32. Declare threshold_ns as u32, not u64. This fixes a Coverity warning. Addresses-Coverity-ID: 1462501 Signed-off-by: Gustavo A. R. Silva [bhelgaas: changelog] Signed-off-by: Bjorn Helgaas Reviewed-by: Andy Shevchenko > --- > drivers/pci/pcie/aspm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c > index 57feef2..8633fc4 100644 > --- a/drivers/pci/pcie/aspm.c > +++ b/drivers/pci/pcie/aspm.c > @@ -322,7 +322,7 @@ static u32 calc_l1ss_pwron(struct pci_dev *pdev, u32 scale, u32 val) > > static void encode_l12_threshold(u32 threshold_us, u32 *scale, u32 *value) > { > - u64 threshold_ns = threshold_us * 1000; > + u32 threshold_ns = threshold_us * 1000; > > /* See PCIe r3.1, sec 7.33.3 and sec 6.18 */ > if (threshold_ns < 32) { > -- > 2.7.4 >