From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754007AbbF3OID (ORCPT ); Tue, 30 Jun 2015 10:08:03 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:45378 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753463AbbF3OH5 (ORCPT ); Tue, 30 Jun 2015 10:07:57 -0400 Message-ID: <5592A2BA.7010604@codeaurora.org> Date: Tue, 30 Jun 2015 09:07:54 -0500 From: Timur Tabi User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:36.0) Gecko/20100101 Firefox/36.0 SeaMonkey/2.33.1 MIME-Version: 1.0 To: Will Deacon CC: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Shanker Donthineni , "awallis@codeaurora.org" , "abhimany@codeaurora.org" , "sboyd@codeaurora.org" , Vipul Gandhi Subject: Re: [PATCH 1/3] hvc_dcc: bind driver to core0 for reads and writes References: <1435344756-20901-1-git-send-email-timur@codeaurora.org> <20150630135815.GK27725@arm.com> In-Reply-To: <20150630135815.GK27725@arm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Will Deacon wrote: >> >Selecting this option will enable code that serializes all console >> >input and output to core 0. The DCC driver will create input and >> >output FIFOs that all cores will use. Reads and writes from/to DCC >> >are handled by a workqueue that runs only core 0. > What happens if CPU0 is hotplugged off? I guess the whole thing just breaks. I don't know what to say. Trace32's DCC window is latched to CPU0. If that CPU is hotplugged off, then I don't think there's a mechanism for Trace32 to migrate to another CPU. It will broken no matter what. That's why this feature is disabled by default. If you're working on an SMP ARM system and using Trace32, you will need this patch. It might be possible for Lauterbach to fix Trace32 to provide this feature internally in some situations (e.g. SMP mode where there's one window for all cores), but not in every situation. I can add a "depends on !CPU_HOTPLUG" to the Kconfig, but I think that's overkill. This is really a "use it if you need it" patch, and DCC is used mostly for debugging. -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation.