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 B2FE8C4167B for ; Mon, 11 Dec 2023 10:11:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234954AbjLKKLB (ORCPT ); Mon, 11 Dec 2023 05:11:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234947AbjLKKK5 (ORCPT ); Mon, 11 Dec 2023 05:10:57 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E30EECF for ; Mon, 11 Dec 2023 02:11:02 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 04C8DC433C8; Mon, 11 Dec 2023 10:11:00 +0000 (UTC) Message-ID: <45fbd63f-068a-433d-9950-e6c645a6068b@xs4all.nl> Date: Mon, 11 Dec 2023 11:10:58 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/2] videobuf2: Add min_reqbufs_allocation field to vb2_queue structure Content-Language: en-US, nl To: Benjamin Gaignard , mchehab@kernel.org, tfiga@chromium.org Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-staging@lists.linux.dev, kernel@collabora.com References: <20231208103908.85874-1-benjamin.gaignard@collabora.com> <20231208103908.85874-3-benjamin.gaignard@collabora.com> From: Hans Verkuil Autocrypt: addr=hverkuil@xs4all.nl; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Benjamin, On 08/12/2023 11:39, Benjamin Gaignard wrote: > Add 'min_reqbufs_allocation' field in vb2_queue structure so drivers > can specificy the minimum number of buffers to allocate when calling > VIDIOC_REQBUFS. > If used this minimum should be higher than the minimum number of > queued buffers needed to start streaming. > > Signed-off-by: Benjamin Gaignard > --- > drivers/media/common/videobuf2/videobuf2-core.c | 1 + > include/media/videobuf2-core.h | 6 ++++++ > 2 files changed, 7 insertions(+) > > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c > index 7b6d89641e66..3bc30d107308 100644 > --- a/drivers/media/common/videobuf2/videobuf2-core.c > +++ b/drivers/media/common/videobuf2/videobuf2-core.c > @@ -866,6 +866,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory, > * Make sure the requested values and current defaults are sane. > */ > num_buffers = max_t(unsigned int, *count, q->min_queued_buffers); This should be changed to 'q->min_queued_buffers + 1'. Without the '+ 1' you wouldn't have a buffer available to return to userspace. > + num_buffers = max_t(unsigned int, num_buffers, q->min_reqbufs_allocation); > num_buffers = min_t(unsigned int, num_buffers, q->max_num_buffers); > memset(q->alloc_devs, 0, sizeof(q->alloc_devs)); > /* I'm missing a WARN_ON in vb2_core_queue_init verifying that min_reqbufs_allocation <= max_num_buffers. Also, min_reqbufs_allocation must be > min_queued_buffers + 1. I also think it might be a good idea to add this to vb2_core_queue_init(): if (!q->min_reqbufs_allocation) q->min_reqbufs_allocation = q->min_queued_buffers + 1; Now we can just use q->min_reqbufs_allocation everywhere in vb2. And with that change you can probably simplify the code, e.g. there is no more need to check q->min_queued_buffers + 1 in the code above. > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h > index 6d11cb724e95..252d34cc47d3 100644 > --- a/include/media/videobuf2-core.h > +++ b/include/media/videobuf2-core.h > @@ -550,6 +550,11 @@ struct vb2_buf_ops { > * @start_streaming can be called. Used when a DMA engine > * cannot be started unless at least this number of buffers > * have been queued into the driver. This needs to be expanded: * VIDIOC_REQBUFS will ensure at least @min_queued_buffers + 1 * buffers will be allocated. Note that VIDIOC_CREATE_BUFS will not * modify the requested buffer count. > + * @min_reqbufs_allocation: the minimum number of buffers allocated when > + * calling VIDIOC_REQBUFS. Used when drivers need a to > + * specify a minimum buffers allocation before setup a queue. > + * If min_queued_buffers < min_queued_buffers then min_queued_buffers > + * is the minimum. I'd rephrase this: * @min_reqbufs_allocation: the minimum number of buffers to be allocated when * calling VIDIOC_REQBUFS. Drivers can set this if there has to * be a certain number of buffers available for the hardware to * work effectively. If set, then @min_reqbufs_allocation must be * larger than @min_queued_buffers + 1. * * This field is only used by VIDIOC_REQBUFS. This allows calling * that ioctl with a buffer count of 1 and it will be automatically * adjusted to a workable buffer count. VIDIOC_CREATE_BUFS will not * modify the requested buffer count. * * If this field is > 3, then it is highly recommended that the * driver implements the V4L2_CID_MIN_BUFFERS_FOR_CAPTURE/OUTPUT * control. Feel free to modify these texts, they are just suggestions. > */ > /* > * Private elements (won't appear at the uAPI book): > @@ -615,6 +620,7 @@ struct vb2_queue { > u32 timestamp_flags; > gfp_t gfp_flags; > u32 min_queued_buffers; > + u32 min_reqbufs_allocation; > > struct device *alloc_devs[VB2_MAX_PLANES]; > Looking through videobuf2-core.c I see one more min_queued_buffers-related issue: In vb2_core_reqbufs() there is this code: if (allocated_buffers < q->min_buffers_needed) ret = -ENOMEM; That should be '< q->min_reqbufs_allocation'. Finally, add a patch updating the test-drivers as per "[PATCH v2 17/36] media: test-drivers: Fix misuse of min_buffers_needed field" + my reply to that. At least the test drivers should use these fields correctly. Regards, Hans