Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751671AbdCNSGf (ORCPT ); Tue, 14 Mar 2017 14:06:35 -0400 Received: from foss.arm.com ([217.140.101.70]:38120 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750744AbdCNSGe (ORCPT ); Tue, 14 Mar 2017 14:06:34 -0400 Subject: Re: [2/2] coresight: Fix reference count for software sources To: Mathieu Poirier References: <1489073232-5093-3-git-send-email-suzuki.poulose@arm.com> Cc: "linux-arm-kernel@lists.infradead.org" , Chunyan Zhang , "linux-kernel@vger.kernel.org" From: Suzuki K Poulose Message-ID: Date: Tue, 14 Mar 2017 18:06:30 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2507 Lines: 63 On 14/03/17 17:40, Mathieu Poirier wrote: > On 14 March 2017 at 11:32, Mathieu Poirier wrote: >> From: "Suzuki K. Poulose" >> >> For software sources (i.e STM), there could be multiple agents >> generating the trace data, unlike the ETMs. So we need to >> properly do the accounting for the active number of users >> to disable the device when the last user goes away. Right >> now, the reference counting is broken for sources as we skip >> the actions when we detect that the source is enabled. >> >> This patch fixes the problem by adding the refcounting for >> software sources, even when they are enabled. >> >> Cc: Mathieu Poirier >> Reported-by: Robert Walker >> Signed-off-by: Suzuki K Poulose >> --- >> drivers/hwtracing/coresight/coresight.c | 13 +++++++++++-- >> 1 file changed, 11 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c >> index 34cd1ed..2da9e39 100644 >> --- a/drivers/hwtracing/coresight/coresight.c >> +++ b/drivers/hwtracing/coresight/coresight.c >> @@ -552,6 +552,7 @@ int coresight_enable(struct coresight_device *csdev) >> int cpu, ret = 0; >> struct coresight_device *sink; >> struct list_head *path; >> + enum coresight_dev_subtype_source subtype = csdev->subtype.source_subtype; > > Checkpatch.pl complains about a line over 80 characters. > >> >> mutex_lock(&coresight_mutex); >> >> @@ -559,8 +560,16 @@ int coresight_enable(struct coresight_device *csdev) >> if (ret) >> goto out; >> >> - if (csdev->enable) >> + if (csdev->enable) { >> + /* >> + * There could be multiple applications driving the software >> + * source. So keep the refcount for each such user when the >> + * source is already enabled. >> + */ >> + if (subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE) >> + atomic_inc(csdev->refcnt); >> goto out; >> + } >> Btw, should we allow the user to turn on the STM from sysfs (echo 1 > $STM/enable_source) ? All STM users should set their policy via ioctls and that in turn turns the device on. So it doesn't make sense for enable_source to really enable the hardware unless someone really opens it. Chunyan, Mathieu, thoughts ? Suzuki