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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 876BFC433E0 for ; Thu, 25 Feb 2021 12:52:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 37F1A64EB7 for ; Thu, 25 Feb 2021 12:52:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233451AbhBYMwF (ORCPT ); Thu, 25 Feb 2021 07:52:05 -0500 Received: from mx2.suse.de ([195.135.220.15]:35508 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233087AbhBYMv6 (ORCPT ); Thu, 25 Feb 2021 07:51:58 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id EC3DDAF5B; Thu, 25 Feb 2021 12:51:16 +0000 (UTC) Date: Thu, 25 Feb 2021 13:51:16 +0100 Message-ID: From: Takashi Iwai To: Anton Yakovlev Cc: , , , "Michael S. Tsirkin" , Jaroslav Kysela , Takashi Iwai , Subject: Re: [PATCH v5 6/9] ALSA: virtio: PCM substream operators In-Reply-To: References: <20210222153444.348390-1-anton.yakovlev@opensynergy.com> <20210222153444.348390-7-anton.yakovlev@opensynergy.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 25 Feb 2021 13:14:37 +0100, Anton Yakovlev wrote: > > On 25.02.2021 11:55, Takashi Iwai wrote: > > On Mon, 22 Feb 2021 16:34:41 +0100, > > Anton Yakovlev wrote: > >> +static int virtsnd_pcm_open(struct snd_pcm_substream *substream) > >> +{ > >> + struct virtio_pcm *vpcm = snd_pcm_substream_chip(substream); > >> + struct virtio_pcm_substream *vss = NULL; > >> + > >> + if (vpcm) { > >> + switch (substream->stream) { > >> + case SNDRV_PCM_STREAM_PLAYBACK: > >> + case SNDRV_PCM_STREAM_CAPTURE: { > > > > The switch() here looks superfluous. The substream->stream must be a > > good value in the callback. If any, you can put WARN_ON() there, but > > I don't think it worth. > > At least it doesn't do any harm. It does -- it makes the readability worse, and that's a very important point. > >> +static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream, > >> + struct snd_pcm_hw_params *hw_params) > >> +{ > > .... > >> + return virtsnd_pcm_msg_alloc(vss, periods, period_bytes); > > > > We have the allocation, but... > > > >> +static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream) > >> +{ > >> + return 0; > > > > ... no release at hw_free()? > > I know that the free is present in the allocator, but it's only for > > re-allocation case, I suppose. > > When the substream stops, sync_ptr waits until the device has completed > all pending messages. This wait can be interrupted either by a signal or > due to a timeout. In this case, the device can still access messages > even after calling hw_free(). It can also issue an interrupt, and the > interrupt handler will also try to access message structures. Therefore, > freeing of already allocated messages occurs either in hw_params() or in > dev->release(), since there it is 100% safe. OK, then it's worth to document it about this object lifecycle. The buffer management of this driver is fairly unique, so otherwise it confuses readers. thanks, Takashi