From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965629AbeCADPC (ORCPT ); Wed, 28 Feb 2018 22:15:02 -0500 Received: from gateway22.websitewelcome.com ([192.185.46.131]:25141 "EHLO gateway22.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965565AbeCADPB (ORCPT ); Wed, 28 Feb 2018 22:15:01 -0500 Subject: Re: [PATCH] PCI/ASPM: Change type of threshold_ns variable to u32 To: Bjorn Helgaas Cc: Andy Shevchenko , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180227231952.GA9001@embeddedor.com> <20180228205546.GL127842@bhelgaas-glaptop.roam.corp.google.com> From: "Gustavo A. R. Silva" Message-ID: <2a893793-b7a0-a13f-4b88-8cf28554d816@embeddedor.com> Date: Wed, 28 Feb 2018 21:14:55 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180228205546.GL127842@bhelgaas-glaptop.roam.corp.google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 189.175.117.58 X-Source-L: No X-Exim-ID: 1erEgN-001Jwn-TB X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: ([192.168.1.67]) [189.175.117.58]:36134 X-Source-Auth: garsilva@embeddedor.com X-Email-Count: 4 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/28/2018 02:55 PM, Bjorn Helgaas wrote: > 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 Thanks, Bjorn. -- Gustavo > 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 >>