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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,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 6A7A1C433E2 for ; Mon, 22 Mar 2021 10:31:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 395D4619AA for ; Mon, 22 Mar 2021 10:31:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230240AbhCVKab (ORCPT ); Mon, 22 Mar 2021 06:30:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53904 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230203AbhCVKaV (ORCPT ); Mon, 22 Mar 2021 06:30:21 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4A593C061574 for ; Mon, 22 Mar 2021 03:30:21 -0700 (PDT) Received: from [192.168.1.111] (91-157-208-71.elisa-laajakaista.fi [91.157.208.71]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id E40F9AD6; Mon, 22 Mar 2021 11:30:18 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1616409019; bh=QfESnKWCsw1J5iOlSJl3uXspHkaRZqtLvylMnAVyR98=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=K0vy77nWv5UhkJMVXghnPM8uLFiHTBuF3sCurITNxrfz5iyXmdtArTrBUZAEQxiV6 7CCZaZnB7X/mWKyKZoZksXg+dwpjJsBtDDBmZVuKReWw58TZkWkyeLNZhcl6WLj7tm rTvR+eZqHov3EOyzXZ9aSeVvarbfEmLsbGzs8oiE= Subject: Re: vb2_queue type question To: Hans Verkuil Cc: Laurent Pinchart , Sakari Ailus , linux-media@vger.kernel.org References: <67107267-69c8-d87d-6579-5e7dac0400fb@xs4all.nl> From: Tomi Valkeinen Message-ID: <37463c0d-7565-ba37-b8e5-9fa5e77e8d11@ideasonboard.com> Date: Mon, 22 Mar 2021 12:30:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <67107267-69c8-d87d-6579-5e7dac0400fb@xs4all.nl> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On 22/03/2021 11:49, Hans Verkuil wrote: > On 22/03/2021 10:18, Tomi Valkeinen wrote: >> Hi Hans, >> >> We were discussing this with Laurent and Sakari, I thought I'd ask if >> you have any feedback on this. >> >> struct vb2_queue has 'type' field, so you can only use a queue for >> buffers of a single type. struct video_device has 'queue' field, so you >> can only use a single queue for a video_device instance. >> >> TI's SoCs have a CSI-2 receiver, with a bunch of DMA engines. The HW >> doesn't care if we are currently capturing pixel buffers or metadata >> buffers (I don't have experience with other HW, but I imagine this >> shouldn't be a rare case). However, due to vb2_queue, the driver needs >> to decide which one to support, which limits the possible use cases. >> >> I was browsing the code, and afaics the type field doesn't do much. It >> is, of course, used to reject queuing buffers of wrong type, and also >> (mostly in mem-2-mem code) to find out if functions are called in input >> or output context. >> >> The latter one could be easily removed by just comparing the given queue >> pointer to a stored pointer (e.g. queue == priv->input_queue). >> >> Do you see any problems if we were to change the type field to >> type_mask, allowing multiple buffer types per queue? Or even remove the >> vb2_queue->type. This raises some questions, like should a queue contain >> only buffers of a single type or can it contain a mix of buffers (I >> think it shouldn't contain a mix of buffers), or can a queue's type_mask >> contain both input and output types (I don't see why not). >> >> An alternate which I tried was creating two vb2_queues, and switching >> the video_device->queue at runtime based on set_format. It kind of >> works, but I think the behavior is a bit unclear, and it might be >> difficult to catch all the corner cases. > > A vb2_queue basically represents a buffer queue that will be fed to a > DMA engine. It assumes that all the buffers are of the same format, > which typically is tied directly to the type. > > The type of a vb2_queue can be changed if you like, but once buffers > are allocated it is fixed and can't be changed again until all buffers > are released. So you can't mix buffers of different types. > > This is actually done in the vivid driver: see vidioc_s_fmt_vbi_cap() > and vidioc_s_fmt_sliced_vbi_cap(): depending on the format the queue > type will be set to either capture raw or sliced VBI. > > The ivtv driver does the same thing. > > So as long as vb2_is_busy() returns false, you are free to change the > queue type. > > There is no need for a type_mask or anything like that. That's up to > the bridge driver to check. The vb2_queue type is there to ensure that > userspace isn't trying to mix buffers of different types, but as long > as no buffers are allocated it doesn't do anything and you are free to > change it. Thanks, this works fine and is simple to manage. Tomi