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Wed, 03 Jun 2020 10:24:18 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 5010CC43391; Wed, 3 Jun 2020 10:24:18 +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 A84B2C433CA; Wed, 3 Jun 2020 10:24:17 +0000 (UTC) MIME-Version: 1.0 Date: Wed, 03 Jun 2020 15:54:17 +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: 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_032444_003003_6D689A6D X-CRM114-Status: GOOD ( 23.01 ) 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, 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. This way, we do not have to introduce any new mode as well. To be exact, in tmc_shutdown() we just disable ETR and then return without unregistering which should not cause any issues since this is shutdown not the remove callback which is a requirement for making coresight modular like below: static void tmc_shutdown(struct amba_device *adev) { unsigned long flags; struct tmc_drvdata *drvdata = amba_get_drvdata(adev); spin_lock_irqsave(&drvdata->spinlock, flags); if (drvdata->mode == CS_MODE_DISABLED) goto out; if (drvdata->config_type == TMC_CONFIG_TYPE_ETR) tmc_etr_disable_hw(drvdata); /* * We do not care about coresight unregister here unlike remove * callback which is required for making coresight modular since * the system is going down after this. */ out: spin_unlock_irqrestore(&drvdata->spinlock, flags); } 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