Received: by 2002:a25:1506:0:0:0:0:0 with SMTP id 6csp5400467ybv;
        Mon, 17 Feb 2020 19:19:37 -0800 (PST)
X-Google-Smtp-Source: APXvYqzUqpSn3/XBk1lLEqBEX58WDi5zsR4FzexJF2U8oPgpeswmGRzSqzwu9uPGgGNIwt3l+7Zt
X-Received: by 2002:aca:e106:: with SMTP id y6mr9499oig.131.1581995977636;
        Mon, 17 Feb 2020 19:19:37 -0800 (PST)
ARC-Seal: i=1; a=rsa-sha256; t=1581995977; cv=none;
        d=google.com; s=arc-20160816;
        b=Hdj2ATSfzi+Ke8mrJXOZ6+Y4sMERXbMYqDMG8yAZu8+NNHx5ALawvnK9nueGSxir9o
         3QFejhCqYgdF64vY48OiU0KaaQzoz37Qn1NkXeQpsX76+jX5F35cw0slvPYCFryPXFo+
         57jja94oQgFPxshToPJuijnbcKkRnlpYwhX7cOhJzFRNxCk6fuyZrmTsiwlRpfiK/M5h
         dGqK/WhgoNoU7kPPj5oEpDoPuLhNK+QdgF0VP13ArKh6xO9A3h14YPGywUhcChBP7e1x
         FoPnMlTi3REzNDuM0c3+BGGECqUslpeUBBKQdfenHcqCgxPckrIrJ9kuh8SCNVLJeMFA
         sD2Q==
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
        h=list-id:precedence:sender:dkim-signature:content-language
         :content-transfer-encoding:in-reply-to:mime-version:user-agent:date
         :message-id:references:cc:to:from:subject;
        bh=ewBeKrm9OD1QPlMgDI7JfmdksrOcR+SVEjMV8XU2Hms=;
        b=sy2lu3AqmQK9eomB2SSOqNQcRA3kacOWtnI+Vl1F7s9fu4XbBDjOYgAisKfLeSj28L
         7EbK+L0ydwJvsjpAuoelQZhgJPsVAiWGjkRQioUafTpATUzL33+8+KHLcgU4niTLm9gP
         OuLZYldmBZeB9moVeTmowasgjyXk5Iq74FdtnGNhAHmLGn89M7UUqqhEa0IbW6uzAOqt
         IChoMbItHb2Vt6XbZzn58ulGD+B1A3KvdzfR2FnDPpGzC4y1mfuIRPSOHW4GQYqbht0k
         oEIhVbdBm2n0iezfm8vzaXYhlB8vzEUizAOCCBINbje5ABArgnlf2/cxYxnPxTDSiRqH
         oXWg==
ARC-Authentication-Results: i=1; mx.google.com;
       dkim=pass header.i=@nvidia.com header.s=n1 header.b=Pfe3ZUEA;
       spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org;
       dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=nvidia.com
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67])
        by mx.google.com with ESMTP id w2si1146025otq.31.2020.02.17.19.19.25;
        Mon, 17 Feb 2020 19:19:37 -0800 (PST)
Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Authentication-Results: mx.google.com;
       dkim=pass header.i=@nvidia.com header.s=n1 header.b=Pfe3ZUEA;
       spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org;
       dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=nvidia.com
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1726445AbgBRDTR (ORCPT <rfc822;utfcpqpk@gmail.com> + 99 others);
        Mon, 17 Feb 2020 22:19:17 -0500
Received: from hqnvemgate25.nvidia.com ([216.228.121.64]:5618 "EHLO
        hqnvemgate25.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1726237AbgBRDTR (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 17 Feb 2020 22:19:17 -0500
Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate25.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA)
        id <B5e4b57930003>; Mon, 17 Feb 2020 19:18:44 -0800
Received: from hqmail.nvidia.com ([172.20.161.6])
  by hqpgpgate101.nvidia.com (PGP Universal service);
  Mon, 17 Feb 2020 19:19:15 -0800
X-PGP-Universal: processed;
        by hqpgpgate101.nvidia.com on Mon, 17 Feb 2020 19:19:15 -0800
Received: from [10.2.163.245] (10.124.1.5) by HQMAIL107.nvidia.com
 (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 18 Feb
 2020 03:19:14 +0000
Subject: Re: [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver
From:   Sowjanya Komatineni <skomatineni@nvidia.com>
To:     Hans Verkuil <hverkuil@xs4all.nl>, <thierry.reding@gmail.com>,
        <jonathanh@nvidia.com>, <frankc@nvidia.com>,
        <helen.koike@collabora.com>, <sboyd@kernel.org>
CC:     <linux-media@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-clk@vger.kernel.org>, <linux-tegra@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <1581704608-31219-1-git-send-email-skomatineni@nvidia.com>
 <1581704608-31219-5-git-send-email-skomatineni@nvidia.com>
 <30e417ba-84e1-63d2-de74-22cfe859bddb@xs4all.nl>
 <920b4276-b2ca-646c-a21b-ca0b9bacf471@nvidia.com>
 <6bb124db-681c-55c1-e328-6e1f766a8bb3@nvidia.com>
 <0f84d37c-105f-8de6-c922-186d2f9ea156@nvidia.com>
 <44fc39f4-8e9f-bcab-8642-fe1cb332016a@xs4all.nl>
 <fb5f1566-9347-8f34-ada0-15c831cbc394@nvidia.com>
 <87c1c97d-abd7-8ca5-0709-d7c64a7d7b39@nvidia.com>
Message-ID: <32ebc124-cb2d-f545-a5a0-d71192af8219@nvidia.com>
Date:   Mon, 17 Feb 2020 19:19:15 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.9.0
MIME-Version: 1.0
In-Reply-To: <87c1c97d-abd7-8ca5-0709-d7c64a7d7b39@nvidia.com>
X-Originating-IP: [10.124.1.5]
X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To
 HQMAIL107.nvidia.com (172.20.187.13)
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: quoted-printable
Content-Language: en-US
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1;
        t=1581995924; bh=ewBeKrm9OD1QPlMgDI7JfmdksrOcR+SVEjMV8XU2Hms=;
        h=X-PGP-Universal:Subject:From:To:CC:References:Message-ID:Date:
         User-Agent:MIME-Version:In-Reply-To:X-Originating-IP:
         X-ClientProxiedBy:Content-Type:Content-Transfer-Encoding:
         Content-Language;
        b=Pfe3ZUEAFyaAkxGvzjwJHC73gXjMlUh4tKlLHOuFRUlSWGfVqsT5MfGzPPvDvFsMj
         OPE77Oi8Nx6rBev4E5KpBWnChpPV9ce0kHdA0Odg2+PkDDxTpWpbVfjzPoYoFhMwVX
         PY4ZCz2oE6GVShWWtpptoEQN12yqXvpBteiEkQIYeWpXmXaez+W3WmeKUnoJFDiXOR
         oWBxDZh7zbCR8BOTFqNZtHzCpzzFcQw9wj57mKRNttZ2oTRX9NGYVy8Sp9nXZJAd/2
         pG6erIqiJPkBYa4lvIWMlGvo5uDFRZNjjIy7Gbhi/cPkW0wQveISiPuVhZ6qpis/Jz
         t9rZXXatojMDw==
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 2/17/20 5:04 PM, Sowjanya Komatineni wrote:
>
> On 2/17/20 4:59 PM, Sowjanya Komatineni wrote:
>>
>> On 2/17/20 12:04 AM, Hans Verkuil wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> On 2/16/20 9:22 PM, Sowjanya Komatineni wrote:
>>>> On 2/16/20 12:11 PM, Sowjanya Komatineni wrote:
>>>>> On 2/16/20 11:54 AM, Sowjanya Komatineni wrote:
>>>>>> On 2/16/20 3:03 AM, Hans Verkuil wrote:
>>>>>>> External email: Use caution opening links or attachments
>>>>>>>
>>>>>>>
>>>>>>> On 2/14/20 7:23 PM, Sowjanya Komatineni wrote:
>>>>>>>> Tegra210 contains a powerful Video Input (VI) hardware controller
>>>>>>>> which can support up to 6 MIPI CSI camera sensors.
>>>>>>>>
>>>>>>>> Each Tegra CSI port can be one-to-one mapped to VI channel and can
>>>>>>>> capture from an external camera sensor connected to CSI or from
>>>>>>>> built-in test pattern generator.
>>>>>>>>
>>>>>>>> Tegra210 supports built-in test pattern generator from CSI to VI.
>>>>>>>>
>>>>>>>> This patch adds a V4L2 media controller and capture driver support
>>>>>>>> for Tegra210 built-in CSI to VI test pattern generator.
>>>>>>>>
>>>>>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
>>>>>>>> ---
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/Kconfig=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0=C2=A0 =
2 +
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/Makefile=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0=C2=A0 1 +
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/Kconfig=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0 10 +
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/Makefile=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0=C2=A0 8 +
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/TODO=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0 10 +
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra-common.h |=C2=A0 23=
9 +++++++
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra-csi.c=C2=A0=C2=A0=
=C2=A0 |=C2=A0 374 ++++++++++
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra-csi.h=C2=A0=C2=A0=
=C2=A0 |=C2=A0 115 ++++
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra-vi.c=C2=A0=C2=A0=C2=
=A0=C2=A0 | 1019
>>>>>>>> ++++++++++++++++++++++++++++
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra-vi.h=C2=A0=C2=A0=C2=
=A0=C2=A0 |=C2=A0=C2=A0 79 +++
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra-video.c=C2=A0 |=C2=
=A0 118 ++++
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra-video.h=C2=A0 |=C2=
=A0=C2=A0 32 +
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra210.c=C2=A0=C2=A0=C2=
=A0=C2=A0 |=C2=A0 767
>>>>>>>> +++++++++++++++++++++
>>>>>>>> =C2=A0=C2=A0 drivers/staging/media/tegra/tegra210.h=C2=A0=C2=A0=C2=
=A0=C2=A0 |=C2=A0 190 ++++++
>>>>>>>> =C2=A0=C2=A0 14 files changed, 2964 insertions(+)
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/Kconfi=
g
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/Makefi=
le
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/TODO
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra-=
common.h
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra-=
csi.c
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra-=
csi.h
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra-=
vi.c
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra-=
vi.h
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra-=
video.c
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra-=
video.h
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra2=
10.c
>>>>>>>> =C2=A0=C2=A0 create mode 100644 drivers/staging/media/tegra/tegra2=
10.h
>>>>>>>>
>>>>>>> <snip>
>>>>>>>
>>>>>>>> +/*
>>>>>>>> + * videobuf2 queue operations
>>>>>>>> + */
>>>>>>>> +static int tegra_channel_queue_setup(struct vb2_queue *vq,
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 unsigned int *=
nbuffers,
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 unsigned int *=
nplanes,
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 unsigned int s=
izes[],
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct device =
*alloc_devs[])
>>>>>>>> +{
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 struct tegra_vi_channel *chan =3D vb2_ge=
t_drv_priv(vq);
>>>>>>>> +
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 if (*nplanes)
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0 return sizes[0] < chan->format.sizeimage ?=20
>>>>>>>> -EINVAL : 0;
>>>>>>>> +
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 *nplanes =3D 1;
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 sizes[0] =3D chan->format.sizeimage;
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 alloc_devs[0] =3D chan->vi->dev;
>>>>>>>> +
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 /*
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * allocate min 3 buffers in queue =
to avoid race between DMA
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * writes and userspace reads.
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 if (*nbuffers < 3)
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0 *nbuffers =3D 3;
>>>>>>> First of all, don't check this here, instead set the struct
>>>>>>> vb2_queue field
>>>>>>> 'min_buffers_needed' to 3 instead.
>>>>>>>
>>>>>>> But the reason given for this check is peculiar: there should=20
>>>>>>> not be
>>>>>>> any
>>>>>>> race at all. Usually the reason for requiring a specific minimum
>>>>>>> number of
>>>>>>> buffers is that the DMA engine needs at least 2 buffers before it
>>>>>>> can start
>>>>>>> streaming: it can't give back a buffer to userspace=20
>>>>>>> (vb2_buffer_done())
>>>>>>> unless there is a second buffer it can start to capture to next. So
>>>>>>> for many
>>>>>>> DMA implementations you need a minimum of 2 buffers: two buffers=20
>>>>>>> for
>>>>>>> the
>>>>>>> DMA engine, one buffer being processed by userspace.
>>>>>>>
>>>>>>> If the driver is starved of buffers it will typically keep=20
>>>>>>> capturing to
>>>>>>> the last buffer until a new buffer is queued.
>>>>>>>
>>>>>>> In any case, once the driver releases a buffer via=20
>>>>>>> vb2_buffer_done()
>>>>>>> the
>>>>>>> buffer memory is no longer owned by the driver.
>>>>>>>
>>>>>>> To be precise, buffer ownership is as follows:
>>>>>>>
>>>>>>> userspace -> VIDIOC_QBUF -> vb2 -> buf_queue -> driver ->
>>>>>>> vb2_buffer_done() -> vb2 -> VIDIOC_DQBUF -> userspace
>>>>>>>
>>>>>>> (vb2 =3D=3D videobuf2 framework)
>>>>>>>
>>>>>>> Note that vb2 never touches the buffer memory.
>>>>>>>
>>>>>>> So if you get a race condition in this driver, then there is=20
>>>>>>> something
>>>>>>> strange going on. It looks like vb2_buffer_done() is called while
>>>>>>> DMA is
>>>>>>> still ongoing, or because the driver really needs to keep one=20
>>>>>>> buffer
>>>>>>> available at all times.
>>>>>>>
>>>>>>> Regards,
>>>>>>>
>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Hans
>>>>>> Thanks Hans.
>>>>>>
>>>>>> On running v4l2-compliance streaming tests for longer run, I noticed
>>>>>> kernel reporting unable to write to read-only memory and with debugs
>>>>>> I observed when this error was reported, I see 2 buffers queued and
>>>>>> both using same address.
>>>>>>
>>>>>> for first buffer capture start thread initiates capture and wakes
>>>>>> done thread to wait for memory write ack and once its done buffer is
>>>>>> released to user space but I see upon buffer released to user space
>>>>>> immediate next buffer capture single shot gets issued (as soon as
>>>>>> single shot is issued frame capture data is written to memory by=20
>>>>>> DMA)
>>>>>> and I see this kernel error of unable to write to read-only memory.
>>>>>>
>>>>>> This error happens rare and happens on long run and all the times of
>>>>>> repro's, I see when other thread releases buffer immediate I see
>>>>>> single shot gets issued as 2 buffers are queued up at the same time
>>>>>> with same DMA address.
>>>>>>
>>>>> Just to be clear, I meant all the times when kernel reports error
>>>>> unable to write to read-only memory, I see 2 buffers gets queued and
>>>>> as the capture start thread and done thread are parallel and when
>>>>> capture thread wakes done thread on receiving FS event, done thread
>>>>> for waiting for memory write happens parallel to next frame capture
>>>>> and I see while vb2_buffer_done happens in done thread next frame
>>>>> single shot has been issues by capture start thread in parallel when
>>>>> it hits this error.
>>>> For low latency, we use 2 threads one thread for capture and wait=20
>>>> for FS
>>>> and on receiving FS even wakes other done thread to wait for memory
>>>> write to finish.
>>>>
>>>> While other done thread waits for memory write to finish, capture=20
>>>> thread
>>>> can start capture for next frame and as soon as single shot is issued
>>>> capture frame is written to memory and as this thread runs in parallel
>>>> to done thread
>>>>
>>>> there is a possibility vb2_buffer_done being called by
>>>> kthread_capture_done while DMA is ongoing by kthread_capture_start=20
>>>> and I
>>>> observed same DMA address being used got both buffers that got=20
>>>> queued at
>>>> same time when it hits this error.
>>> "buffers that got queued": you mean that=20
>>> tegra_channel_buffer_queue() is
>>> called twice with different buffers (i.e. with different buffer=20
>>> index values)
>>> but with the same DMA address?
>>
>> yes I see buf_queue invoked twice and both using same DMA address.
>>
>> I did not monitored buf index when I repro'd with debugs.
>>
>>> That should not happen (unless the first buffer was returned with
>>> vb2_buffer_done() before the second buffer was queued).
>>>
>>> Can you provide more details? E.g. buffer index, memory model used when
>>> streaming, total number of buffers allocated by REQBUFS.
>>
>> memory type is MMAP. buffer count is 1. Didn't monitored buf index=20
>> but when this happened as count is 1 so I think it might be index 0.
>>
>> But what I noticed is on running long hours rarely this repro's and=20
>> at the time of repro, I see 2 immediate buf_queue with same DMA address.
>>
>> 1st buffer capture starts and received FS and wakes other thread to=20
>> wait for MW_ACK_DONE and when capture thread executes for 2nd buffer=20
>> right as soon as single shot bit is set which writes captured data to=20
>> memory kernel error of unable to write to read-only memory happens.
>>
>> I couldn't add more debugs to confirm if 1st buffer release finished=20
>> or not by the time 2nd buffer single shot is issued but I see=20
>> MW_ACK_DONE event received for 1st buffer.
>>
>> Adding more debugs does not repro this kernel error and that could be=20
>> because delays with debug messages helps time interval b/w buffer=20
>> release and next buffer single shot.
>>
>>>
>>> I would like to fully understand this. Just increasing the minimum=20
>>> number
>>> of buffers, while reasonable by itself, *does* feel like it is just
>>> hiding the symptoms.
>>>
>>> Regards,
>>>
>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Hans
>>
>> kthread for capture start and kthread for done which waiting for=20
>> memory write to happen runs in parallel.
>>
>> Its hard to confirm if buffer done is invoked by kthread_done at same=20
>> time of kthread_capture DMA write of next frame as adding debugs has=20
>> impact on delay and doesnt repro with more debugs.
>>
>> But just increasing no.of min buffers to 3 doesnt repro at all and I=20
>> never see 2 buffer queue requests with same DMA address as min=20
>> buffers are 3.
>>
> Will add debugs and monitor with index again and check for repro by=20
> removing min buffers to re-confirm ...

Without specifying min buffers needed, I am able to repro again.

Noticed the buf that got released previously is the one that gets next=20
into the queue. So I don't see same buffer being used b/w captures.=20
Somehow I might have misinterpreted timing from logs earlier.

This time repro happened after streaming stop and on next streaming=20
buf_prepare call back (with in tegra_channel_buffer_prepare)

Earlier repro's call trace also showed all the time it happened in=20
tegra_channel_buffer_prepare but I noticed that happened when capture=20
start thread was running in parallel and right on single shot issued.

So, looks like I misunderstood that it happened b/w issuing single shot=20
and releasing buffer but could be its being reported during buffer=20
prepare itself.

All the times of repro, call trace shows it happens during buf_prepare.

[=C2=A0=C2=A0 41.213146] Unable to handle kernel write to read-only memory =
at=20
virtual address ffff0000f5c3fff8
[=C2=A0=C2=A0 41.222012] Mem abort info:
[=C2=A0=C2=A0 41.224807]=C2=A0=C2=A0 ESR =3D 0x9600004f
[=C2=A0=C2=A0 41.227852]=C2=A0=C2=A0 EC =3D 0x25: DABT (current EL), IL =3D=
 32 bits
[=C2=A0=C2=A0 41.233160]=C2=A0=C2=A0 SET =3D 0, FnV =3D 0
[=C2=A0=C2=A0 41.236204]=C2=A0=C2=A0 EA =3D 0, S1PTW =3D 0
[=C2=A0=C2=A0 41.239344] Data abort info:
[=C2=A0=C2=A0 41.242225]=C2=A0=C2=A0 ISV =3D 0, ISS =3D 0x0000004f
[=C2=A0=C2=A0 41.246058]=C2=A0=C2=A0 CM =3D 0, WnR =3D 1
[=C2=A0=C2=A0 41.249026] swapper pgtable: 4k pages, 48-bit VAs, pgdp=3D0000=
000081498000
[=C2=A0=C2=A0 41.255733] [ffff0000f5c3fff8] pgd=3D000000017f1f8003,=20
pud=3D000000017ec06003, pmd=3D000000017ea57003, pte=3D0060000175c3f793
[=C2=A0=C2=A0 41.266345] Internal error: Oops: 9600004f [#1] PREEMPT SMP
[=C2=A0=C2=A0 41.271905] Modules linked in: panel_simple tegra_drm=20
snd_hda_codec_hdmi snd_hda_tegra crct10dif_ce snd_hda_codec cec=20
drm_kms_helper snd_hda_core lp855x_bl drm pwm_tegra ip_tables x_tables=20
ipv6 nf_defrag_ipv6
[=C2=A0=C2=A0 41.290401] CPU: 3 PID: 532 Comm: v4l2-compliance Tainted: G=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=20
W=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 5.6.0-rc1-00035-g6a105c1c=
479a-dirty #1
[=C2=A0=C2=A0 41.300902] Hardware name: NVIDIA Jetson TX1 Developer Kit (DT=
)
[=C2=A0=C2=A0 41.306807] pstate: 60000005 (nZCv daif -PAN -UAO)
[=C2=A0=C2=A0 41.311593] pc : tegra_channel_buffer_prepare+0x34/0x88
[=C2=A0=C2=A0 41.316807] lr : __buf_prepare+0x1c4/0x230
[=C2=A0=C2=A0 41.320891] sp : ffff800011f5baa0
[=C2=A0=C2=A0 41.324195] x29: ffff800011f5baa0 x28: ffff0000f58cc100
[=C2=A0=C2=A0 41.329494] x27: ffff800011f5bc58 x26: ffff80001100b780
[=C2=A0=C2=A0 41.334792] x25: ffff0000f81f1608 x24: ffff0000f7be7c00
[=C2=A0=C2=A0 41.340091] x23: 00000000c058565d x22: 0000000000000000
[=C2=A0=C2=A0 41.345390] x21: ffff0000f81f16e8 x20: 0000000000000000
[=C2=A0=C2=A0 41.350688] x19: ffff0000f5c40000 x18: 0000000000000000
[=C2=A0=C2=A0 41.355986] x17: 0000000000000000 x16: 0000000000000000
[=C2=A0=C2=A0 41.361285] x15: ffff0000f8553800 x14: 0000000000000000
[=C2=A0=C2=A0 41.366583] x13: 003f480000000000 x12: 003f500000000000
[=C2=A0=C2=A0 41.371881] x11: 0000000100000000 x10: 0000000000000000
[=C2=A0=C2=A0 41.377180] x9 : 0000000000000000 x8 : ffff0000f5c40258
[=C2=A0=C2=A0 41.382478] x7 : 0000000000000030 x6 : 0000000000000001
[=C2=A0=C2=A0 41.387776] x5 : 0000000000000000 x4 : 00000000003f4800
[=C2=A0=C2=A0 41.393074] x3 : 00000000003f4800 x2 : 00000000003f4800
[=C2=A0=C2=A0 41.398373] x1 : ffff0000f81f1080 x0 : ffff0000f5c40000
[=C2=A0=C2=A0 41.403671] Call trace:
[=C2=A0=C2=A0 41.406109]=C2=A0 tegra_channel_buffer_prepare+0x34/0x88
[=C2=A0=C2=A0 41.410974]=C2=A0 __buf_prepare+0x1c4/0x230
[=C2=A0=C2=A0 41.414713]=C2=A0 vb2_core_prepare_buf+0x94/0x110
[=C2=A0=C2=A0 41.418971]=C2=A0 vb2_prepare_buf+0x74/0xa8
[=C2=A0=C2=A0 41.422710]=C2=A0 vb2_ioctl_prepare_buf+0x54/0x60
[=C2=A0=C2=A0 41.426970]=C2=A0 v4l_prepare_buf+0x44/0x58
[=C2=A0=C2=A0 41.430707]=C2=A0 __video_do_ioctl+0x228/0x3e8
[=C2=A0=C2=A0 41.434705]=C2=A0 video_usercopy+0x1cc/0x4d0
[=C2=A0=C2=A0 41.438531]=C2=A0 video_ioctl2+0x14/0x20
[=C2=A0=C2=A0 41.442010]=C2=A0 v4l2_ioctl+0x44/0x68
[=C2=A0=C2=A0 41.445316]=C2=A0 v4l2_compat_ioctl32+0x21c/0x1420
[=C2=A0=C2=A0 41.449665]=C2=A0 __arm64_compat_sys_ioctl+0xc8/0x108
[=C2=A0=C2=A0 41.454273]=C2=A0 el0_svc_common.constprop.2+0xb0/0x168
[=C2=A0=C2=A0 41.459051]=C2=A0 do_el0_svc_compat+0x18/0x38
[=C2=A0=C2=A0 41.462964]=C2=A0 el0_sync_compat_handler+0x13c/0x194
[=C2=A0=C2=A0 41.467570]=C2=A0 el0_sync_compat+0x144/0x180
[=C2=A0=C2=A0 41.471483] Code: b9407802 eb02007f 540001e8 b9007404 (f81f800=
1)
[=C2=A0=C2=A0 41.477563] ---[ end trace 051c84051f60870a ]---

>>
>>>>>> With using minimum 3 buffers, this issue doesnt happen at all from
>>>>>> almost 72 hours of testing.
>>>>>>
>>>>>>
>>>>>> Will try with setting vb2 queue field min_buffers_needed as 3=20
>>>>>> instead
>>>>>> of adding check in queue setup.
>>>>>>
>>>>>>>> +
>>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 return 0;
>>>>>>>> +}