From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 48F167FA35 for ; Wed, 4 Sep 2019 16:16:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732764AbfIDQGE (ORCPT ); Wed, 4 Sep 2019 12:06:04 -0400 Received: from mail-io1-f67.google.com ([209.85.166.67]:47050 "EHLO mail-io1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733009AbfIDQGD (ORCPT ); Wed, 4 Sep 2019 12:06:03 -0400 Received: by mail-io1-f67.google.com with SMTP id x4so45261485iog.13 for ; Wed, 04 Sep 2019 09:06:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=5lhWafqYFmhotqOeEvQEWgPd+ZPMMqTqg3Hle4q+xhU=; b=CHLprMwQX4fDdOh9+SC0j0oKqhpRV5SxjXmh82FD18bndq7o9RVQv3xwg1LlxDAY44 LHMcYBPRJESuihYLmkWujLc9RW4n6/POEmyeQJQMWa4nxbe334mV63xyugLbOowTvPvY mblFSd9J/wgEeV2yeFxP7I+FL+xUs7diHC+xH5JLi/ZbgTa0xW6G5TrQ3aY7aMdivj/H fJwyuCjddPAENUptyq951q8DPWi767SWU7TrIgd9KuvKSOm+02Yrhj+XlwiiLVkQvo63 piPY0o5VxYy9OFGvwB7GC6avakut7yxVQiAvZIm6568lpuf3mP5SbEFIUmguCQqzT/WJ oRPQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=5lhWafqYFmhotqOeEvQEWgPd+ZPMMqTqg3Hle4q+xhU=; b=tXyrwa4qlrc3AUILZStaLNoKdkLqJaEhNsePu3yI7S2jONg9iE3tK7s2gMsEnBSX08 5qkoXzAlty1eYIUk2+mAaa+nv6SkNeoY3synrOTXsgCVNxYWHRvjYYMT7yMWE+nwC8gu yp72FFNMbxqrqg4+BtET2E1ep96LefD9uhxFw374mqVmRlJeQbZb4b+UHrn30q/RiVCh oHnbOxShTVKiQ52Gde31XUBe4ue2d+N7Jzt3IWPzzHuBywp3e3tqatobkyadQjBABqEL PTlRxeJMm/TOl8SzknFAq9/V7tEbYE3IPNFivjhnfb+VkMY2uysDqR05LSSgR1SqrLJY HrcQ== X-Gm-Message-State: APjAAAUil/lX7kmpAGrr4/5g54b2VmaSviAJ5Wpi9GFB52fZMaYUrxc2 ryZOTC3s3Sr2zKRqUS1wvah5IL/9pAZV2pGzUUoESns/ X-Google-Smtp-Source: APXvYqz4yu3QVTFmHphFpeszsph5mwZpIGJqJee0ZteodLoeZweGPlU1B4ldAcZ9Edn8Xfx0kYtihi/V2VCWYezetpI= X-Received: by 2002:a6b:b213:: with SMTP id b19mr4404471iof.58.1567613162647; Wed, 04 Sep 2019 09:06:02 -0700 (PDT) MIME-Version: 1.0 References: <20190829213321.4092-1-mike.leach@linaro.org> <20190829213321.4092-10-mike.leach@linaro.org> <20190903195951.GA25008@kroah.com> <20190904054809.GB4511@kroah.com> In-Reply-To: <20190904054809.GB4511@kroah.com> From: Mathieu Poirier Date: Wed, 4 Sep 2019 10:05:51 -0600 Message-ID: Subject: Re: [PATCH v2 09/11] coresight: etm4x: docs: Update ABI doc for sysfs features added. To: Greg KH Cc: Mike Leach , linux-arm-kernel , Coresight ML , "open list:DOCUMENTATION" , "Suzuki K. Poulose" , Jon Corbet Content-Type: text/plain; charset="UTF-8" Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, 3 Sep 2019 at 23:48, Greg KH wrote: > > On Tue, Sep 03, 2019 at 04:51:40PM -0600, Mathieu Poirier wrote: > > On Tue, 3 Sep 2019 at 13:59, Greg KH wrote: > > > > > > On Thu, Aug 29, 2019 at 10:33:19PM +0100, Mike Leach wrote: > > > > Update document to include the new sysfs features added during this > > > > patchset. > > > > > > > > Updated to reflect the new sysfs component nameing schema. > > > > > > > > Signed-off-by: Mike Leach > > > > --- > > > > .../testing/sysfs-bus-coresight-devices-etm4x | 183 +++++++++++------- > > > > 1 file changed, 115 insertions(+), 68 deletions(-) > > > > > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x b/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > index 36258bc1b473..112c50ae9986 100644 > > > > --- a/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > +++ b/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x > > > > @@ -1,4 +1,4 @@ > > > > -What: /sys/bus/coresight/devices/.etm/enable_source > > > > +What: /sys/bus/coresight/devices/etm/enable_source > > > > > > You are renaming sysfs directories that have been around since: > > > > > > > Date: April 2015 > > > > > > ??? > > > > > > Really? > > > > > > That's brave. > > > > > > When I worked on the coresight sysfs ABI a while back I specifically > > added it at the "testing" level as I was well aware that things could > > change in the future. According to the guidelines in the > > documentation userspace can rely on it which was accurate since the > > interface didn't change for 4 years. But the guidelines also mention > > that changes can occur before the interfaces are move to stables, and > > that programs are encouraged to manifest their interest by adding > > their name to the "users" field. > > > > The interface was changed in 5.2 to support coresight from ACPI and > > make things easier to understand for users. It is a lot more > > intuitive to associate an ETM tracer with the CPU it belongs to by > > referring to the CPU number than the memory mapped address. Given the > > "testing" status of the interface and the absence of registered users > > I decided to move forward with the change. If "testing" is too strict > > for that I suggest to add an "experimental" category where it would be > > more acceptable to change things as subsystems mature. > > "testing" is not really "testing" if you have userspace tools/programs > assuming the location and contents of specific files in sysfs. > > You can change things in sysfs by creating new files, but to do > wholesale renaming like you did here can be very dangerous as you might > be breaking things. Yes, something I have definitely considered. > Usually new files are created, not existing ones > moved. In this case it would have meant a new symbolic link for every coresight device, so twice a many entries under $(SYS)/bus/coresight/device/. That would have been a lot of clutter and an increasing source of problems as the number of CPU and sinks increases. To me, and given the permissive definition of "testing" found in the documentation, a clean break was a better option. > > What tools use these today? What is going to break? Other than local shell scripts I am not aware of any tools using these today. I am certainly open to discuss a better alternative but right now, I just don't see one. > > thanks, > greg k-h