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 94B28C433F5 for ; Thu, 13 Jan 2022 09:11:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233933AbiAMJLe (ORCPT ); Thu, 13 Jan 2022 04:11:34 -0500 Received: from foss.arm.com ([217.140.110.172]:41500 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233887AbiAMJLZ (ORCPT ); Thu, 13 Jan 2022 04:11:25 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 62C26113E; Thu, 13 Jan 2022 01:11:25 -0800 (PST) Received: from e121896.arm.com (unknown [10.57.35.134]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id DD13D3F766; Thu, 13 Jan 2022 01:11:22 -0800 (PST) From: James Clark To: suzuki.poulose@arm.com, mathieu.poirier@linaro.org, coresight@lists.linaro.org, leo.yan@linaro.com, mike.leach@linaro.org Cc: James Clark , Leo Yan , John Garry , Will Deacon , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Subject: [PATCH v2 6/6] Documentation: coresight: Expand branch broadcast documentation Date: Thu, 13 Jan 2022 09:10:55 +0000 Message-Id: <20220113091056.1297982-7-james.clark@arm.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20220113091056.1297982-1-james.clark@arm.com> References: <20220113091056.1297982-1-james.clark@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now that there is a way of enabling branch broadcast via perf, mention the possible use cases and known limitations. Signed-off-by: James Clark --- .../trace/coresight/coresight-etm4x-reference.rst | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/Documentation/trace/coresight/coresight-etm4x-reference.rst b/Documentation/trace/coresight/coresight-etm4x-reference.rst index 0439b4006227..ec336575919c 100644 --- a/Documentation/trace/coresight/coresight-etm4x-reference.rst +++ b/Documentation/trace/coresight/coresight-etm4x-reference.rst @@ -656,7 +656,15 @@ Bit assignments shown below:- ETM_MODE_BB **description:** - Set to enable branch broadcast if supported in hardware [IDR0]. + Set to enable branch broadcast if supported in hardware [IDR0]. The primary use for this feature + is when code is patched dynamically at run time and the full program flow may not be able to be + reconstructed using only conditional branches. + + Choosing this option will result in a significant increase in the amount of trace generated - + possible danger of overflows, or fewer instructions covered. Note, that this option also + overrides any setting of :ref:`ETM_MODE_RETURNSTACK `, so where a branch + broadcast range overlaps a return stack range, return stacks will not be available for that + range. .. _coresight-cycle-accurate: -- 2.28.0