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 AB668C001DF for ; Wed, 26 Jul 2023 16:59:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230190AbjGZQ76 (ORCPT ); Wed, 26 Jul 2023 12:59:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43198 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229866AbjGZQ7z (ORCPT ); Wed, 26 Jul 2023 12:59:55 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9D40A188; Wed, 26 Jul 2023 09:59:54 -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 52E172F4; Wed, 26 Jul 2023 10:00:37 -0700 (PDT) Received: from [10.57.82.133] (unknown [10.57.82.133]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A95703F67D; Wed, 26 Jul 2023 09:59:51 -0700 (PDT) Message-ID: <9c3b4a97-bbe2-a978-b000-9562123af523@arm.com> Date: Wed, 26 Jul 2023 17:59:50 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH V6 0/6] coresight: etm4x: Migrate ACPI AMBA devices to platform driver To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org, coresight@lists.linaro.org, gregkh@linuxfoundation.org, rafael@kernel.org Cc: Ganapatrao Kulkarni , Steve Clevenger , Rob Herring , Frank Rowand , Russell King , Len Brown , Sudeep Holla , Lorenzo Pieralisi , Mathieu Poirier , Mike Leach , Leo Yan , devicetree@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org References: <20230710062500.45147-1-anshuman.khandual@arm.com> From: Suzuki K Poulose In-Reply-To: <20230710062500.45147-1-anshuman.khandual@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/07/2023 07:24, 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 6.5-rc1. > > Changes in V6: > > - Rebased on 6.5-rc1 > I have queued this version for v6.6, should appear on coresight/next soon. Suzuki