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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BE817C7EE23 for ; Tue, 23 May 2023 15:52:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237641AbjEWPwI (ORCPT ); Tue, 23 May 2023 11:52:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235682AbjEWPwG (ORCPT ); Tue, 23 May 2023 11:52:06 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3412A91; Tue, 23 May 2023 08:52:04 -0700 (PDT) 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 3BE94139F; Tue, 23 May 2023 08:52:49 -0700 (PDT) Received: from bogus (e103737-lin.cambridge.arm.com [10.1.197.49]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C4AC13F840; Tue, 23 May 2023 08:52:01 -0700 (PDT) Date: Tue, 23 May 2023 16:51:59 +0100 From: Sudeep Holla To: Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, coresight@lists.linaro.org, suzuki.poulose@arm.com, Ganapatrao Kulkarni , Steve Clevenger , Rob Herring , Frank Rowand , Russell King , Greg Kroah-Hartman , "Rafael J. Wysocki" , Len Brown , Sudeep Holla , Lorenzo Pieralisi , Mathieu Poirier , Mike Leach , Leo Yan , devicetree@vger.kernel.org, linux-acpi@vger.kernel.org Subject: Re: [PATCH V4 0/6] coresight: etm4x: Migrate ACPI AMBA devices to platform driver Message-ID: <20230523155159.na2wfhuhb7fqr3cy@bogus> References: <20230523044553.1525048-1-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230523044553.1525048-1-anshuman.khandual@arm.com> Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Tue, May 23, 2023 at 10:15:47AM +0530, Anshuman Khandual wrote: > CoreSight ETM4x devices could be accessed either via MMIO (handled via > amba_driver) or CPU system instructions (handled via platform driver). But > this has the following issues : > > - Each new CPU comes up with its own PID and thus we need to keep on > adding the "known" PIDs to get it working with AMBA driver. While > the ETM4 architecture (and CoreSight architecture) defines way to > identify a device as ETM4. Thus older kernels won't be able to > "discover" a newer CPU, unless we add the PIDs. > > - With ACPI, the ETM4x devices have the same HID to identify the device > irrespective of the mode of access. This creates a problem where two > different drivers (both AMBA based driver and platform driver) would > hook into the "HID" and could conflict. e.g., if AMBA driver gets > hold of a non-MMIO device, the probe fails. If we have single driver > hooked into the given "HID", we could handle them seamlessly, > irrespective of the mode of access. > > - CoreSight is heavily dependent on the runtime power management. With > ACPI, amba_driver doesn't get us anywhere with handling the power > and thus one need to always turn the power ON to use them. Moving to > platform driver gives us the power management for free. > > Due to all of the above, we are moving ACPI MMIO based etm4x devices to be > supported via tha platform driver. The series makes the existing platform > driver generic to handle both type of the access modes. Although existing > AMBA driver would still continue to support DT based etm4x MMIO devices. > Although some problems still remain, such as manually adding PIDs for all > new AMBA DT based devices. > > The series applies on 6.4-rc3. > Tested on Juno with some hacked up UEFI f/w. Tested-by: Sudeep Holla -- Regards, Sudeep