From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0015FC433E0 for ; Wed, 3 Jun 2020 12:14:54 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B8DFF20678 for ; Wed, 3 Jun 2020 12:14:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="GbGrNuTH"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="KtnEXaDk" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B8DFF20678 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-ID:References:In-Reply-To:Subject:To:From: Date:MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=dWlRirIrVnyrOTK9xTCgHOfRpvkuvrPsph/7WDexu54=; b=GbGrNuTH41DntseemiM6us15F dsVbmvIT1g14K7M+xUhGf/YHgJqmjsBIcn/EPMleWqg2wxS2HcgdHwjtcVkW7cuD1My4Q2fJvFyBA JHJudwZIqeFSRKVk5MNv15G6TCrI3baPHoRHONkbxiQ+zkDWirwJAF2IB5RlhjM6EObd1eOHzDjdD xB6VxxP69pjIgJ+6+gUeHC3Dxc5lXk1lffdJ5n4Az4K+CI7c3l0sQiW7/DRJ+BpZjZ1PBXpp5Gcc5 VcsR+JPo046ivjUvt4fw5u6DuWDcDLu1VWwlYtlOV8mGlqnIu3ak2Gznox80W0pfIEHM/8i6U92QN CzLlIpxKQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jgSII-0000sf-As; Wed, 03 Jun 2020 12:14:54 +0000 Received: from m43-7.mailgun.net ([69.72.43.7]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jgSIF-0000sH-4j for linux-arm-kernel@lists.infradead.org; Wed, 03 Jun 2020 12:14:52 +0000 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1591186491; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=JbS524Cnw2NfPr05sWSsjesDpzR7nsPveFPmkLicFCE=; b=KtnEXaDkzv0bbXoUlMwPm5D0L4wv+IZgGWjLQgpQck68YR8lj7gF3uAxyUAjU1fn2FX2fzNA /clOweAX0AgmlrDivKUCuN+q9PtWfgeaTsYQvZeyddseGsDxyD3GmcpKVH9rfGVtmV+C+rg/ yn33aJ7DuJxeVCBW1abj5VEn4s0= X-Mailgun-Sending-Ip: 69.72.43.7 X-Mailgun-Sid: WyJiYzAxZiIsICJsaW51eC1hcm0ta2VybmVsQGxpc3RzLmluZnJhZGVhZC5vcmciLCAiYmU5ZTRhIl0= Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n12.prod.us-west-2.postgun.com with SMTP id 5ed7943646d39fc0a20b4b10 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Wed, 03 Jun 2020 12:14:46 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 65953C433CB; Wed, 3 Jun 2020 12:14:46 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan) by smtp.codeaurora.org (Postfix) with ESMTPSA id A3729C433CA; Wed, 3 Jun 2020 12:14:45 +0000 (UTC) MIME-Version: 1.0 Date: Wed, 03 Jun 2020 17:44:45 +0530 From: Sai Prakash Ranjan To: Mike Leach Subject: Re: [PATCH 2/2] coresight: tmc: Add shutdown callback for TMC ETR/ETF In-Reply-To: References: <28123d1e19f235f97555ee36a5ed8b52d20cbdea.1590947174.git.saiprakash.ranjan@codeaurora.org> <20200601212858.GB24287@xps15> <6d759cc28628ea72767c1304883630eb@codeaurora.org> Message-ID: <4a09cd2e054836d85f2e024ca4435e91@codeaurora.org> X-Sender: saiprakash.ranjan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200603_051451_495368_09EC044D X-CRM114-Status: GOOD ( 26.22 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mathieu Poirier , Suzuki K Poulose , linux-arm-msm@vger.kernel.org, Coresight ML , Linux Kernel Mailing List , Stephen Boyd , robin.murphy@arm.com, linux-arm-kernel Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Mike, On 2020-06-03 16:57, Mike Leach wrote: > Hi, > > On Wed, 3 Jun 2020 at 11:24, Sai Prakash Ranjan > wrote: >> >> Hi Mike, >> >> Thanks again for looking at this. >> >> On 2020-06-03 03:42, Mike Leach wrote: >> [...] >> >> >> >> >> SMMU/IOMMU won't be able to do much here as it is the client's >> >> responsiblity to >> >> properly shutdown and SMMU device link just makes sure that >> >> SMMU(supplier) shutdown is >> >> called only after its consumers shutdown callbacks are called. >> > >> > I think this use case can be handled slightly differently than the >> > general requirements for modular CoreSight drivers. >> > >> > What is needed here is a way of stopping the underlying ETR hardware >> > from issuing data to the SMMU, until the entire device has been shut >> > down, in a way that does not remove the driver, breaking existing >> > references and causing a system crash. >> > >> > We could introduce a new mode to the ETR driver - e.g. >> > CS_MODE_SHUTDOWN. >> > >> > At the end of the block tmc_shutdown(struct amba_device *adev), set >> > drvdata->mode to CS_MODE_SHUTDOWN & remove the coresight_unregister(). >> > This new mode can be used to prevent the underlying hardware from >> > being able to restart until the device is re-powered. >> > >> > This mode can be detected in the code that enables / disables the ETR >> > and handled appropriately (updates to tmc_enable_etr_sink and >> > tmc_disable_etr_sink). >> > This mode will persist until the device is re-started - but because we >> > are on the device shutdown path this is not an issue. >> > >> > This should leave the CoreSight infrastructure stable until the >> > drivers are shut down normally as part of the device power down >> > process. >> > >> >> Sounds good to me, but if the coresight_unregister() is the trouble >> point >> causing these crashes, then can't we just remove that from >> tmc_shutdown() >> callback? This would be like maintaining the same behaviour as now >> where >> on reboot/shutdown we basically don't do anything except for disabling >> ETR. > > No - the new mode prevents race conditions where the thread shutting > down the SMMU does the ETR shutdown, but then another thread happens > to be trying to start trace and restarts the ETR. > It also prevents the condition Mathieu discussed where a thread might > be attempting to shutdown trace - this could try to disable the > hardware again re-releasing resources/ re-flushing and waiting for > stop. > I do not think there will a race between SMMU shutdown and ETR shutdown. Driver core takes care of calling SMMU shutdown after its consumer shutdown callbacks via device link, otherwise there would already be bugs in all other client drivers. Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel