From patchwork Thu Nov 30 12:58:12 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hans Verkuil X-Patchwork-Id: 13474369 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C846D38DE0 for ; Thu, 30 Nov 2023 13:03:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: by smtp.kernel.org (Postfix) with ESMTPSA id 985A6C433C9; Thu, 30 Nov 2023 13:03:50 +0000 (UTC) From: Hans Verkuil To: linux-media@vger.kernel.org Cc: "Dr . David Alan Gilbert" , Deborah Brouwer , Hans Verkuil Subject: [PATCH 3/3] media: videobuf2: request more buffers for vb2_read Date: Thu, 30 Nov 2023 13:58:12 +0100 Message-ID: <86ad4808718ff07ab8ac64b62170b789c16b2581.1701349092.git.hverkuil-cisco@xs4all.nl> X-Mailer: git-send-email 2.42.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 The vb2 read support requests 1 buffer, leaving it to the driver to increase this number to something that works. Unfortunately, drivers do not deal with this reliably, and in fact this caused problems for the bttv driver and reading from /dev/vbiX, causing every other VBI frame to be all 0. Instead, request as the number of buffers whatever is the maximum of 2 and q->min_buffers_needed+1. In order to start streaming you need at least q->min_buffers_needed queued buffers, so add 1 buffer for processing. And if that field is 0, then choose 2 (again, one buffer is being filled while the other one is being processed). This certainly makes more sense than requesting just 1 buffer, and the VBI bttv support is now working again. It turns out that the old videobuf1 behavior of bttv was to allocate 8 (video) and 4 (vbi) buffers when used with read(). After the vb2 conversion that changed to 2 for both. With this patch it is 3, which is really all you need. Signed-off-by: Hans Verkuil Fixes: b7ec3212a73a ("media: bttv: convert to vb2") Tested-by: Dr. David Alan Gilbert --- drivers/media/common/videobuf2/videobuf2-core.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c index 8c1df829745b..40d89f29fa33 100644 --- a/drivers/media/common/videobuf2/videobuf2-core.c +++ b/drivers/media/common/videobuf2/videobuf2-core.c @@ -2735,9 +2735,14 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read) return -EBUSY; /* - * Start with count 1, driver can increase it in queue_setup() + * Start with q->min_buffers_needed + 1, driver can increase it in + * queue_setup() + * + * 'min_buffers_needed' buffers need to be queued up before you + * can start streaming, plus 1 for userspace (or in this case, + * kernelspace) processing. */ - count = 1; + count = max(2, q->min_buffers_needed + 1); dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n", (read) ? "read" : "write", count, q->fileio_read_once,