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b=qq4rWcd23mQvuQkR3wBtdwtfpT4dtJKNB2pbfz2gHxuVSC+5DXcb5UueiBhWQN64XAxC3d1WgUeKtndWIyEH5mO50iiAyqQzNZos6MKMOUpkr/CcYohiJNFk4kvyz9+WrubJNdmQQIkA98tJF+BedzT1CIFb7w38LKXeO5m2cKk= Authentication-Results-Original: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=arm.com; Received: from PAVPR08MB9674.eurprd08.prod.outlook.com (2603:10a6:102:31d::14) by AM7PR08MB5367.eurprd08.prod.outlook.com (2603:10a6:20b:dd::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.451.5; Fri, 18 Sep 2026 11:14:12 +0000 Received: from PAVPR08MB9674.eurprd08.prod.outlook.com ([fe80::6f25:3681:7c97:ea2e]) by PAVPR08MB9674.eurprd08.prod.outlook.com ([fe80::6f25:3681:7c97:ea2e%5]) with mapi id 15.21.0451.004; Fri, 18 Sep 2026 11:14:12 +0000 Message-ID: <89b18b1e-65ca-4e97-b827-90d360b9e881@arm.com> Date: Fri, 18 Sep 2026 12:14:10 +0100 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 1/9] coresight: etm4x: prohibit modifying ss_status and cntr_val while session is enabled To: Yeoreum Yun , James Clark , Leo Yan , Greg Kroah-Hartman , Mathieu Poirier , coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev Cc: Suzuki K Poulose , Alexander Shishkin , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , nd@arm.com References: <20260915-separate_etm_cfg_v2-v11-0-d2b258d51747@arm.com> <20260915-separate_etm_cfg_v2-v11-1-d2b258d51747@arm.com> Content-Language: en-US From: Mike Leach In-Reply-To: <20260915-separate_etm_cfg_v2-v11-1-d2b258d51747@arm.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: twCJCAVfrYi7wd3HiAZU0tmsdGiU7TkX85Ybdbf2vk8n5bVqbFmk9bl748/eNe/XhFSG5vndpq23voB5Z1gbwm6TPhIbi0KT5BBfbJFmv6DLR/7UswyEwbcecLi0kgogFfmiP0slSbbd4i6Jysqwp/I80W0pRX2AH4x83uUotbOvJux+22PvA+KrkFzf5snbm1rdiZ2HwIxfd2oQ8TKq5ta/dpTfuGrAxL6pElIQaZpH2N16Fzl9Zw4ApATS7pxc91sfCPTVKQpTo7mbQ3tMqy5F3aVh6t9DaVFuRMBTYbvpmjBKbprARZGOGS+3uiekras7mh147yavEDBYarQfwvHGlOZ4gsfe6DVcGKMy3wtk6UEinJIE1jICeWWRgQmdC372m+g8ULa0RRGeqLhl654XNABbJjw665lMfFvUaMJxH9DioVw53U56VND9emkm X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Sep 2026 11:14:45.9973 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: eacd6864-b6f1-4718-dd78-08df15760bf6 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB1PEPF000509F3.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS2PR08MB8648 Hi, Preventing a write to the counter value register is correct, but protecting the ss_status is redundant. On 9/15/26 12:34, Yeoreum Yun wrote: > ss_status and cntr_val are overwritten with the values read from the > corresponding registers by etm4_disable_hw() when the session is disabled. > > This means that any changes to these values made while the session is > enabled would be lost when the session is disabled. > > Therefore, prohibit modifying ss_status and cntr_val while the session is > enabled. > > Signed-off-by: Yeoreum Yun > --- > drivers/hwtracing/coresight/coresight-etm4x-sysfs.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c > index cc6cdd3ae29d5..8d73248b840a6 100644 > --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c > +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c > @@ -1613,6 +1613,8 @@ static ssize_t cntr_val_store(struct device *dev, > return -EINVAL; > if (val > ETM_CNTR_MAX_VAL) > return -EINVAL; > + if (coresight_get_mode(drvdata->csdev)) > + return -EBUSY; > > raw_spin_lock(&drvdata->spinlock); > idx = config->cntr_idx; > @@ -1797,6 +1799,8 @@ static ssize_t sshot_ctrl_store(struct device *dev, > > if (kstrtoul(buf, 16, &val)) > return -EINVAL; > + if (coresight_get_mode(drvdata->csdev)) > + return -EBUSY; > This is protecting a write clearing the STATUS bit in TRCSSCSR - but this is cleared automatically when next time the hardware is enabled in etm4_enable_hw(). So the write to ss_status in this function is redundant as is this protection. The actual write to the targeted control register will persist. > raw_spin_lock(&drvdata->spinlock); > idx = config->ss_idx; > @@ -1847,6 +1851,8 @@ static ssize_t sshot_pe_ctrl_store(struct device *dev, > > if (kstrtoul(buf, 16, &val)) > return -EINVAL; > + if (coresight_get_mode(drvdata->csdev)) > + return -EBUSY; > > raw_spin_lock(&drvdata->spinlock); > idx = config->ss_idx; > as above Regards Mike