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 81958C83F19 for ; Tue, 29 Aug 2023 14:07:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236774AbjH2OGt (ORCPT ); Tue, 29 Aug 2023 10:06:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236865AbjH2OGk (ORCPT ); Tue, 29 Aug 2023 10:06:40 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 666D118F; Tue, 29 Aug 2023 07:06:36 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 037EB1F45B; Tue, 29 Aug 2023 14:06:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1693317995; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=bRHPiHCMm5kQciIqN85NnbPa+/D3qdXc+l72vu74acc=; b=Icu3cYn7A3Kh+pBbrf1rF9LltMScuNV/n0baffUrrjtxAYQ+ncJ4dOsKx6w6MYDBJFnROM NOZOnUkNeXEfIv6Uzbn6FhcQoZLsSFce/t+hcdRNEgz2BAmWW7Zzy+NHG0xwjbRgQNPOat 8Pc2awNUB1gXfd7t5bzLKWoU8zhUeVg= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1693317995; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=bRHPiHCMm5kQciIqN85NnbPa+/D3qdXc+l72vu74acc=; b=ddNrhpwtKRvVRK5RzwIkRRwEEzp36nl+O26eBAnst4HGo76Ah9V9YRErUFvt6TJHJs4oiz xApRR/StlVseWQAg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 6B875138E2; Tue, 29 Aug 2023 14:06:34 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id G+1JGWr77WQMcwAAMHmgww (envelope-from ); Tue, 29 Aug 2023 14:06:34 +0000 Date: Tue, 29 Aug 2023 16:06:33 +0200 Message-ID: <87sf82t02e.wl-tiwai@suse.de> From: Takashi Iwai To: Wesley Cheng Cc: Pierre-Louis Bossart , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v4 31/32] sound: usb: card: Allow for rediscovery of connected USB SND devices In-Reply-To: <2c0e76ab-1e3a-70d6-24dc-32b2e66c2a3a@quicinc.com> References: <20230725023416.11205-1-quic_wcheng@quicinc.com> <20230725023416.11205-32-quic_wcheng@quicinc.com> <671a524d-b4c8-78d8-33de-40170a23d189@linux.intel.com> <87wmyotk74.wl-tiwai@suse.de> <2c0e76ab-1e3a-70d6-24dc-32b2e66c2a3a@quicinc.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Mon, 28 Aug 2023 23:25:14 +0200, Wesley Cheng wrote: > > Hi Takashi, > > On 7/25/2023 2:27 AM, Takashi Iwai wrote: > > On Tue, 25 Jul 2023 11:15:11 +0200, > > Pierre-Louis Bossart wrote: > >> > >> > >> > >> On 7/25/23 04:34, Wesley Cheng wrote: > >>> In case of notifying SND platform drivers of connection events, some of > >>> these use cases, such as offloading, require an ASoC USB backend device to > >>> be initialized before the events can be handled. If the USB backend device > >>> has not yet been probed, this leads to missing initial USB audio device > >>> connection events. > >>> > >>> Expose an API that traverses the usb_chip array for connected devices, and > >>> to call the respective connection callback registered to the SND platform > >>> driver. > >>> > >>> Signed-off-by: Wesley Cheng > >>> --- > >>> sound/usb/card.c | 19 +++++++++++++++++++ > >>> sound/usb/card.h | 2 ++ > >>> 2 files changed, 21 insertions(+) > >>> > >>> diff --git a/sound/usb/card.c b/sound/usb/card.c > >>> index 365f6d978608..27a89aaa0bf3 100644 > >>> --- a/sound/usb/card.c > >>> +++ b/sound/usb/card.c > >>> @@ -170,6 +170,25 @@ struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx, > >>> } > >>> EXPORT_SYMBOL_GPL(snd_usb_find_suppported_substream); > >>> +/* > >>> + * in case the platform driver was not ready at the time of USB SND > >>> + * device connect, expose an API to discover all connected USB devices > >>> + * so it can populate any dependent resources/structures. > >>> + */ > >>> +void snd_usb_rediscover_devices(void) > >>> +{ > >>> + int i; > >>> + > >>> + mutex_lock(®ister_mutex); > >>> + for (i = 0; i < SNDRV_CARDS; i++) { > >>> + if (usb_chip[i]) > >>> + if (platform_ops && platform_ops->connect_cb) > >>> + platform_ops->connect_cb(usb_chip[i]); > >> > >> what happens if the USB device is removed while the platform device adds > >> a port? > > > > That should be protected by the register_mutex. But there can be > > other races (see below :) > > > >> This sounds super-racy to me. It's the same set of problems we're having > >> between audio and display/DRM, I would be surprised if this function > >> dealt with all corner cases of insertion/removal, bind/unbind. > > > > Yes, we need to be more careful about binding. > > > > For example, in the current patch set, I see no way to prevent > > unloading snd-usb-audio-qmi module, and it allows user to cut off the > > stuff during operation, which may break things while the kernel is > > running the code of the unloaded module. You need to have a proper > > module refcount management for avoiding such a scenario. Most of > > drivers don't need it because ALSA core part already takes care of > > it. But in this case, it requires a manual adjustment. > > > > Sorry for the delayed response...this was routed to another folder, > and missed it. > > I see, that is a valid situation, so I think the best way to address > it is to do something like the following: > > static void __exit qc_usb_audio_offload_exit(void) > { > ... > snd_usb_unregister_platform_ops(); > for (idx = 0; idx < SNDRV_CARDS; idx++) > qc_usb_audio_offload_disconnect(uadev[idx].chip); > > We'll first unregister the platform ops, so that we get no further > connect/disconnect CBs, and then we'll forcefully ensure that all > devices are removed/cleaned. Part of the USB offload disconnect > sequence will also forcefully stop the offload path on the external > DSP by issuing a disconnect indication QMI message. > > Then we can safely clean up the rest of the resources. We do have > refcounting in place for several of the other structures, but I think > in the module exit case, we need to ensure the offload path is stopped > fully. Yes, the proper disconnection procedure is mandatory. In addition, you can have a module refcount increment upon the card binding, too. This may prevent the unexpected exit (although it's often still possible to unbind via sysfs). thanks, Takashi