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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 C7370C0650F for ; Tue, 30 Jul 2019 16:28:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BA75206E0 for ; Tue, 30 Jul 2019 16:28:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731236AbfG3Q2R (ORCPT ); Tue, 30 Jul 2019 12:28:17 -0400 Received: from imap1.codethink.co.uk ([176.9.8.82]:52538 "EHLO imap1.codethink.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725889AbfG3Q2R (ORCPT ); Tue, 30 Jul 2019 12:28:17 -0400 Received: from [167.98.27.226] (helo=[10.35.6.253]) by imap1.codethink.co.uk with esmtpsa (Exim 4.84_2 #1 (Debian)) id 1hsUyy-0002cI-8m; Tue, 30 Jul 2019 17:28:12 +0100 Subject: Re: [alsa-devel] [PATCH v2 3/3] ASoC: TDA7802: Add turn-on diagnostic routine To: Mark Brown Cc: Mark Rutland , devicetree@vger.kernel.org, alsa-devel@alsa-project.org, Charles Keepax , Kuninori Morimoto , Kirill Marinushkin , Liam Girdwood , Marco Felsch , Annaliese McDermond , Takashi Iwai , Paul Cercueil , Vinod Koul , Rob Herring , Srinivas Kandagatla , Jerome Brunet , linux-kernel@vger.kernel.org, Cheng-Yi Chiang References: <20190730120937.16271-1-thomas.preston@codethink.co.uk> <20190730120937.16271-4-thomas.preston@codethink.co.uk> <20190730141935.GF4264@sirena.org.uk> <45156592-a90f-b4f8-4d30-9631c03f1280@codethink.co.uk> <20190730155027.GJ4264@sirena.org.uk> From: Thomas Preston Message-ID: <9b47a360-3b62-b968-b8d5-8639dc4b468d@codethink.co.uk> Date: Tue, 30 Jul 2019 17:28:11 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190730155027.GJ4264@sirena.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/07/2019 16:50, Mark Brown wrote: > On Tue, Jul 30, 2019 at 04:25:56PM +0100, Thomas Preston wrote: >> On 30/07/2019 15:19, Mark Brown wrote: > >>> It is unclear what this mutex usefully protects, it only gets taken when >>> writing to the debugfs file to trigger this diagnostic mode but doesn't >>> do anything to control interactions with any other code path in the >>> driver. > >> If another process reads the debugfs node "diagnostic" while the turn-on >> diagnostic mode is running, this mutex prevents the second process >> restarting the diagnostics. > >> This is redundant if debugfs reads are atomic, but I don't think they are. > > Like I say it's not just debugfs though, there's the standard driver > interface too. > Ah right, I understand. So if we run the turn-on diagnostics routine, there's nothing stopping anyone from interacting with the device in other ways. I guess there's no way to share that mutex with ALSA? In that case, it doesn't matter if this mutex is there or not - this feature is incompatible. How compatible do debugfs interfaces have to be? I was under the impression anything goes. I would argue that the debugfs is better off for having the mutex so that no one re-reads "diagnostic" within the 5s poll timeout. Alternatively, this diagnostic feature could be handled with an external-handler kcontrol SOC_SINGLE_EXT? I'm not sure if this is an atomic interface either. What would be acceptable?