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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 A40B5C43381 for ; Fri, 22 Feb 2019 10:52:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6EDA420818 for ; Fri, 22 Feb 2019 10:52:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550832777; bh=I+h2kg3NkqZoczMCw5mdOzpOm4A8AG/Bs6CF9uKFfoQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=DCiU1ObuM9W+3VqS0DLKwSbiN/HTC96BDk5kVcZArdUqDmZ9MidyqO3TUpNl1SZ9W QEHHE3As773hg2TpiU2KuFzxVYTSQSH6rObgxLT7aXyR4e8tu1p8DY/d2K7frEp1xv P2FJcwoUadyUx2+eaa0kHddjPEtlshk9K/039gww= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726763AbfBVKwz (ORCPT ); Fri, 22 Feb 2019 05:52:55 -0500 Received: from mail.kernel.org ([198.145.29.99]:52332 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726072AbfBVKwz (ORCPT ); Fri, 22 Feb 2019 05:52:55 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C264920818; Fri, 22 Feb 2019 10:52:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550832774; bh=I+h2kg3NkqZoczMCw5mdOzpOm4A8AG/Bs6CF9uKFfoQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ffAzru6YdKmfCFWxs5pvRaI2g2wh88RTn0IKvDS5GQ6O15oe7+GTBHKooGG3GoWcK ZAx9FO/T4f6tcFFZOFHeClH+rDTgfTXRUuFojXOJM68idgwO4qo99052G5sVxg7fTM qt63DxSfnZajMW+nk/aG81XeBLH7DGKxWchJQb+Q= Date: Fri, 22 Feb 2019 11:52:51 +0100 From: Greg KH To: Laurent Pinchart Cc: Bjorn Andersson , Vaishali Thakkar , andy.gross@linaro.org, david.brown@linaro.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, rafael@kernel.org, vkoul@kernel.org Subject: Re: [PATCH v2 3/5] soc: qcom: socinfo: Expose custom attributes Message-ID: <20190222105251.GA28554@kroah.com> References: <20190220045829.6852-1-vaishali.thakkar@linaro.org> <20190221121841.GA32108@pendragon.ideasonboard.com> <20190221155742.GD2122@tuxbook-pro> <20190221221359.GD3485@pendragon.ideasonboard.com> <20190222071616.GA2306@kroah.com> <20190222095145.GA3522@pendragon.ideasonboard.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190222095145.GA3522@pendragon.ideasonboard.com> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 22, 2019 at 11:51:45AM +0200, Laurent Pinchart wrote: > Hi Greg, > > On Fri, Feb 22, 2019 at 08:16:16AM +0100, Greg KH wrote: > > On Fri, Feb 22, 2019 at 12:13:59AM +0200, Laurent Pinchart wrote: > > > On Thu, Feb 21, 2019 at 07:57:42AM -0800, Bjorn Andersson wrote: > > > > On Thu 21 Feb 04:18 PST 2019, Laurent Pinchart wrote: > > > > > On Wed, Feb 20, 2019 at 10:28:29AM +0530, Vaishali Thakkar wrote: > > > > > > The Qualcomm socinfo provides a number of additional attributes, > > > > > > add these to the socinfo driver and expose them via debugfs > > > > > > functionality. > > > > > > > > > > What is the use case for these attributes ? I fear they will be used in > > > > > production systems, and that would require debugfs in production, which > > > > > isn't a good idea. If you need to expose those attributes for anything > > > > > else than debugging then we need a proper API, likely sysfs-based. > > > > > > > > The use case of these attributes, beyond development/debugging, are > > > > unfortunately somewhat unknown and is the reason why they where moved to > > > > debugfs from the earlier attempts to upstream this. > > > > > > > > I think the production requirements at hand prohibits debugfs to be > > > > present, so attributes that are required beyond development/debugging > > > > purposes would have to be migrated out to sysfs - but the idea here is > > > > that such migration would have come with the missing motivation to add > > > > them there today. > > > > > > If the use case is just debug/development, would it be enough to print > > > this information in the kernel log at boot time ? I may be a bit > > > paranoid, but I always worry about API abuse :-( > > > > Putting stuff in debugfs should be fine. No system should ever rely on > > debugfs for a properly running system as it is being disabled on almost > > all "sane" systems (Android included). If a vendor relies on this > > information for a properly working system, then it does not belong in > > debugfs. > > There's certainly no disagreement about that, my concern is about > vendors who will enable debugfs to access information they need just > because it's there. Then they run a huge risk of relying on it. > Do I assume correctly we can "break the debugfs ABI" in mainline by > changing the format of the information if needed ? Yes. The only "rule" of debugfs is that there is no rule :) Please, break it every-other release if you want, no userspace tools _should_ be relying on it.[1] thanks, greg k-h [1] Yes, I know Android currently relies on debugfs for a number of crash-dump type of things in ion and binder, but there is active work upstream in AOSP to remove that dependancy as no Android device should ever have debugfs mounted on a "normal" system for the security reasons alone.