Message-ID: <fc7b975a-dffa-4826-7ae5-40abb1f16b3d@nvidia.com>
Date:   Wed, 19 Feb 2020 08:22:20 -0800
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Hans Verkuil <hverkuil@...all.nl>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <frankc@...dia.com>,
        <helen.koike@...labora.com>, <sboyd@...nel.org>
CC:     <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-clk@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver


On 2/19/20 7:08 AM, Hans Verkuil wrote:
> External email: Use caution opening links or attachments
>
>
> On 2/18/20 4:19 AM, Sowjanya Komatineni wrote:
>> 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@...dia.com>
>>>>>>>>>> ---
>>>>>>>>>>     drivers/staging/media/Kconfig              |    2 +
>>>>>>>>>>     drivers/staging/media/Makefile             |    1 +
>>>>>>>>>>     drivers/staging/media/tegra/Kconfig        |   10 +
>>>>>>>>>>     drivers/staging/media/tegra/Makefile       |    8 +
>>>>>>>>>>     drivers/staging/media/tegra/TODO           |   10 +
>>>>>>>>>>     drivers/staging/media/tegra/tegra-common.h |  239 +++++++
>>>>>>>>>>     drivers/staging/media/tegra/tegra-csi.c    |  374 ++++++++++
>>>>>>>>>>     drivers/staging/media/tegra/tegra-csi.h    |  115 ++++
>>>>>>>>>>     drivers/staging/media/tegra/tegra-vi.c     | 1019
>>>>>>>>>> ++++++++++++++++++++++++++++
>>>>>>>>>>     drivers/staging/media/tegra/tegra-vi.h     |   79 +++
>>>>>>>>>>     drivers/staging/media/tegra/tegra-video.c  |  118 ++++
>>>>>>>>>>     drivers/staging/media/tegra/tegra-video.h  |   32 +
>>>>>>>>>>     drivers/staging/media/tegra/tegra210.c     |  767
>>>>>>>>>> +++++++++++++++++++++
>>>>>>>>>>     drivers/staging/media/tegra/tegra210.h     |  190 ++++++
>>>>>>>>>>     14 files changed, 2964 insertions(+)
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/Kconfig
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/Makefile
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/TODO
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra-common.h
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra-csi.c
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra-csi.h
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra-vi.c
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra-vi.h
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra-video.c
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra-video.h
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra210.c
>>>>>>>>>>     create mode 100644 drivers/staging/media/tegra/tegra210.h
>>>>>>>>>>
>>>>>>>>> <snip>
>>>>>>>>>
>>>>>>>>>> +/*
>>>>>>>>>> + * videobuf2 queue operations
>>>>>>>>>> + */
>>>>>>>>>> +static int tegra_channel_queue_setup(struct vb2_queue *vq,
>>>>>>>>>> +                                  unsigned int *nbuffers,
>>>>>>>>>> +                                  unsigned int *nplanes,
>>>>>>>>>> +                                  unsigned int sizes[],
>>>>>>>>>> +                                  struct device *alloc_devs[])
>>>>>>>>>> +{
>>>>>>>>>> +     struct tegra_vi_channel *chan = vb2_get_drv_priv(vq);
>>>>>>>>>> +
>>>>>>>>>> +     if (*nplanes)
>>>>>>>>>> +             return sizes[0] < chan->format.sizeimage ?
>>>>>>>>>> -EINVAL : 0;
>>>>>>>>>> +
>>>>>>>>>> +     *nplanes = 1;
>>>>>>>>>> +     sizes[0] = chan->format.sizeimage;
>>>>>>>>>> +     alloc_devs[0] = chan->vi->dev;
>>>>>>>>>> +
>>>>>>>>>> +     /*
>>>>>>>>>> +      * allocate min 3 buffers in queue to avoid race between DMA
>>>>>>>>>> +      * writes and userspace reads.
>>>>>>>>>> +      */
>>>>>>>>>> +     if (*nbuffers < 3)
>>>>>>>>>> +             *nbuffers = 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
>>>>>>>>> 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
>>>>>>>>> (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
>>>>>>>>> for
>>>>>>>>> the
>>>>>>>>> DMA engine, one buffer being processed by userspace.
>>>>>>>>>
>>>>>>>>> If the driver is starved of buffers it will typically keep
>>>>>>>>> capturing to
>>>>>>>>> the last buffer until a new buffer is queued.
>>>>>>>>>
>>>>>>>>> In any case, once the driver releases a buffer via
>>>>>>>>> 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 == videobuf2 framework)
>>>>>>>>>
>>>>>>>>> Note that vb2 never touches the buffer memory.
>>>>>>>>>
>>>>>>>>> So if you get a race condition in this driver, then there is
>>>>>>>>> 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
>>>>>>>>> buffer
>>>>>>>>> available at all times.
>>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>>
>>>>>>>>>            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
>>>>>>>> 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
>>>>>> 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
>>>>>> 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
>>>>>> and I
>>>>>> observed same DMA address being used got both buffers that got
>>>>>> queued at
>>>>>> same time when it hits this error.
>>>>> "buffers that got queued": you mean that
>>>>> tegra_channel_buffer_queue() is
>>>>> called twice with different buffers (i.e. with different buffer
>>>>> 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
>>>> 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
>>>> 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
>>>> wait for MW_ACK_DONE and when capture thread executes for 2nd buffer
>>>> right as soon as single shot bit is set which writes captured data to
>>>> 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
>>>> or not by the time 2nd buffer single shot is issued but I see
>>>> MW_ACK_DONE event received for 1st buffer.
>>>>
>>>> Adding more debugs does not repro this kernel error and that could be
>>>> because delays with debug messages helps time interval b/w buffer
>>>> release and next buffer single shot.
>>>>
>>>>> I would like to fully understand this. Just increasing the minimum
>>>>> number
>>>>> of buffers, while reasonable by itself, *does* feel like it is just
>>>>> hiding the symptoms.
>>>>>
>>>>> Regards,
>>>>>
>>>>>           Hans
>>>> kthread for capture start and kthread for done which waiting for
>>>> memory write to happen runs in parallel.
>>>>
>>>> Its hard to confirm if buffer done is invoked by kthread_done at same
>>>> time of kthread_capture DMA write of next frame as adding debugs has
>>>> impact on delay and doesnt repro with more debugs.
>>>>
>>>> But just increasing no.of min buffers to 3 doesnt repro at all and I
>>>> never see 2 buffer queue requests with same DMA address as min
>>>> buffers are 3.
>>>>
>>> Will add debugs and monitor with index again and check for repro by
>>> 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
>> into the queue. So I don't see same buffer being used b/w captures.
>> Somehow I might have misinterpreted timing from logs earlier.
>>
>> This time repro happened after streaming stop and on next streaming
>> buf_prepare call back (with in tegra_channel_buffer_prepare)
>>
>> Earlier repro's call trace also showed all the time it happened in
>> tegra_channel_buffer_prepare but I noticed that happened when capture
>> 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
>> and releasing buffer but could be its being reported during buffer
>> prepare itself.
>>
>> All the times of repro, call trace shows it happens during buf_prepare.
>>
>> [   41.213146] Unable to handle kernel write to read-only memory at
>> virtual address ffff0000f5c3fff8
> This is weird: tegra_channel_buffer_prepare doesn't access any of the
> actual buffer memory, it just reads data from structs like vb2_buffer, etc.
>
> This indicates a memory overwrite or something similar. Enabling KASAN
> in the kernel and poisoning freed memory caused the following (100% reproducible)
> crash with 'v4l2-ctl --stream-mmap':
>
> [  135.698408] BUG: KASAN: slab-out-of-bounds in tegra_channel_buffer_prepare+0x5c/0x100
> [  135.706277] Write of size 8 at addr ffff0000c9cfdff8 by task v4l2-ctl/3030
> [  135.713179]
> [  135.714687] CPU: 2 PID: 3030 Comm: v4l2-ctl Tainted: G        W         5.6.0-rc1-arm64 #48
> [  135.723076] Hardware name: NVIDIA Jetson TX1 Developer Kit (DT)
> [  135.729023] Call trace:
> [  135.731490]  dump_backtrace+0x0/0x278
> [  135.735172]  show_stack+0x14/0x20
> [  135.738510]  dump_stack+0xe0/0x134
> [  135.741933]  print_address_description.isra.0+0x68/0x348
> [  135.747270]  __kasan_report+0x114/0x214
> [  135.751126]  kasan_report+0xc/0x18
> [  135.754546]  __asan_store8+0x94/0xb8
> [  135.758142]  tegra_channel_buffer_prepare+0x5c/0x100
> [  135.763133]  __buf_prepare+0x1fc/0x508
> [  135.766902]  vb2_core_qbuf+0x484/0x7c8
> [  135.770672]  vb2_qbuf+0x100/0x148
> [  135.774004]  vb2_ioctl_qbuf+0x90/0xa8
> [  135.777688]  v4l_qbuf+0x54/0x68
> [  135.780847]  __video_do_ioctl+0x288/0x5a0
> [  135.784879]  video_usercopy+0x1f0/0x640
> [  135.788735]  video_ioctl2+0x14/0x1c
> [  135.792244]  v4l2_ioctl+0x98/0xb0
> [  135.795580]  ksys_ioctl+0x2fc/0x10c8
> [  135.799175]  __arm64_sys_ioctl+0x40/0x58
> [  135.803120]  do_el0_svc+0xb8/0x228
> [  135.806542]  el0_sync_handler+0x14c/0x2a8
> [  135.810572]  el0_sync+0x140/0x180
> [  135.813902]
> [  135.815403] Allocated by task 3028:
> [  135.818913]  save_stack+0x24/0xb0
> [  135.822247]  __kasan_kmalloc.isra.0+0xc0/0xe0
> [  135.826626]  kasan_kmalloc+0xc/0x18
> [  135.830133]  __kmalloc+0x198/0x2e8
> [  135.833554]  __vb2_queue_alloc+0xa4/0x858
> [  135.837584]  vb2_core_reqbufs+0x360/0x648
> [  135.841613]  vb2_ioctl_reqbufs+0xe4/0x140
> [  135.845644]  v4l_reqbufs+0x64/0x78
> [  135.849064]  __video_do_ioctl+0x288/0x5a0
> [  135.853095]  video_usercopy+0x1f0/0x640
> [  135.856952]  video_ioctl2+0x14/0x1c
> [  135.860459]  v4l2_ioctl+0x98/0xb0
> [  135.863793]  ksys_ioctl+0x2fc/0x10c8
> [  135.867387]  __arm64_sys_ioctl+0x40/0x58
> [  135.871331]  do_el0_svc+0xb8/0x228
> [  135.874750]  el0_sync_handler+0x14c/0x2a8
> [  135.878779]  el0_sync+0x140/0x180
> [  135.882109]
> [  135.883609] Freed by task 3028:
> [  135.886767]  save_stack+0x24/0xb0
> [  135.890099]  __kasan_slab_free+0x108/0x180
> [  135.894215]  kasan_slab_free+0x10/0x18
> [  135.897982]  kfree+0x9c/0x2d0
> [  135.900965]  __vb2_queue_free+0x774/0xb30
> [  135.904996]  vb2_core_reqbufs+0x138/0x648
> [  135.909026]  vb2_ioctl_reqbufs+0xe4/0x140
> [  135.913059]  v4l_reqbufs+0x64/0x78
> [  135.916479]  __video_do_ioctl+0x288/0x5a0
> [  135.920510]  video_usercopy+0x1f0/0x640
> [  135.924367]  video_ioctl2+0x14/0x1c
> [  135.927875]  v4l2_ioctl+0x98/0xb0
> [  135.931209]  ksys_ioctl+0x2fc/0x10c8
> [  135.934804]  __arm64_sys_ioctl+0x40/0x58
> [  135.938748]  do_el0_svc+0xb8/0x228
> [  135.942169]  el0_sync_handler+0x14c/0x2a8
> [  135.946199]  el0_sync+0x140/0x180
> [  135.949528]
> [  135.951030] The buggy address belongs to the object at ffff0000c9cfd000
> [  135.951030]  which belongs to the cache kmalloc-2k of size 2048
> [  135.963604] The buggy address is located 2040 bytes to the right of
> [  135.963604]  2048-byte region [ffff0000c9cfd000, ffff0000c9cfd800)
> [  135.976091] The buggy address belongs to the page:
> [  135.980909] page:fffffe0003073e00 refcount:1 mapcount:0 mapping:ffff0000dc00ef80 index:0x0 compound_mapcount: 0
> [  135.991046] flags: 0x2fffc00000010200(slab|head)
> [  135.995691] raw: 2fffc00000010200 fffffe0003073600 0000000300000003 ffff0000dc00ef80
> [  136.003473] raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
> [  136.011252] page dumped because: kasan: bad access detected
> [  136.016848]
> [  136.018349] Memory state around the buggy address:
> [  136.023164]  ffff0000c9cfde80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  136.030423]  ffff0000c9cfdf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  136.037681] >ffff0000c9cfdf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [  136.044935]                                                                 ^
> [  136.052104]  ffff0000c9cfe000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [  136.059362]  ffff0000c9cfe080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [  136.066617] ==================================================================
> [  136.073871] Disabling lock debugging due to kernel taint
>
> Note: I had to disable the nouveau driver since that also has a KASAN bug in
> v5.6-rc1.
>
> This happens with the driver as-posted, so with a 3 buffer minimum.
>
> Hopefully this will help you find the root cause of this issue.
>
> Regards,
>
>          Hans
Thanks Hans. Probably dma address is not aligned properly. Will check.
>
>> [   41.222012] Mem abort info:
>> [   41.224807]   ESR = 0x9600004f
>> [   41.227852]   EC = 0x25: DABT (current EL), IL = 32 bits
>> [   41.233160]   SET = 0, FnV = 0
>> [   41.236204]   EA = 0, S1PTW = 0
>> [   41.239344] Data abort info:
>> [   41.242225]   ISV = 0, ISS = 0x0000004f
>> [   41.246058]   CM = 0, WnR = 1
>> [   41.249026] swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000081498000
>> [   41.255733] [ffff0000f5c3fff8] pgd=000000017f1f8003,
>> pud=000000017ec06003, pmd=000000017ea57003, pte=0060000175c3f793
>> [   41.266345] Internal error: Oops: 9600004f [#1] PREEMPT SMP
>> [   41.271905] Modules linked in: panel_simple tegra_drm
>> snd_hda_codec_hdmi snd_hda_tegra crct10dif_ce snd_hda_codec cec
>> drm_kms_helper snd_hda_core lp855x_bl drm pwm_tegra ip_tables x_tables
>> ipv6 nf_defrag_ipv6
>> [   41.290401] CPU: 3 PID: 532 Comm: v4l2-compliance Tainted: G
>> W         5.6.0-rc1-00035-g6a105c1c479a-dirty #1
>> [   41.300902] Hardware name: NVIDIA Jetson TX1 Developer Kit (DT)
>> [   41.306807] pstate: 60000005 (nZCv daif -PAN -UAO)
>> [   41.311593] pc : tegra_channel_buffer_prepare+0x34/0x88
>> [   41.316807] lr : __buf_prepare+0x1c4/0x230
>> [   41.320891] sp : ffff800011f5baa0
>> [   41.324195] x29: ffff800011f5baa0 x28: ffff0000f58cc100
>> [   41.329494] x27: ffff800011f5bc58 x26: ffff80001100b780
>> [   41.334792] x25: ffff0000f81f1608 x24: ffff0000f7be7c00
>> [   41.340091] x23: 00000000c058565d x22: 0000000000000000
>> [   41.345390] x21: ffff0000f81f16e8 x20: 0000000000000000
>> [   41.350688] x19: ffff0000f5c40000 x18: 0000000000000000
>> [   41.355986] x17: 0000000000000000 x16: 0000000000000000
>> [   41.361285] x15: ffff0000f8553800 x14: 0000000000000000
>> [   41.366583] x13: 003f480000000000 x12: 003f500000000000
>> [   41.371881] x11: 0000000100000000 x10: 0000000000000000
>> [   41.377180] x9 : 0000000000000000 x8 : ffff0000f5c40258
>> [   41.382478] x7 : 0000000000000030 x6 : 0000000000000001
>> [   41.387776] x5 : 0000000000000000 x4 : 00000000003f4800
>> [   41.393074] x3 : 00000000003f4800 x2 : 00000000003f4800
>> [   41.398373] x1 : ffff0000f81f1080 x0 : ffff0000f5c40000
>> [   41.403671] Call trace:
>> [   41.406109]  tegra_channel_buffer_prepare+0x34/0x88
>> [   41.410974]  __buf_prepare+0x1c4/0x230
>> [   41.414713]  vb2_core_prepare_buf+0x94/0x110
>> [   41.418971]  vb2_prepare_buf+0x74/0xa8
>> [   41.422710]  vb2_ioctl_prepare_buf+0x54/0x60
>> [   41.426970]  v4l_prepare_buf+0x44/0x58
>> [   41.430707]  __video_do_ioctl+0x228/0x3e8
>> [   41.434705]  video_usercopy+0x1cc/0x4d0
>> [   41.438531]  video_ioctl2+0x14/0x20
>> [   41.442010]  v4l2_ioctl+0x44/0x68
>> [   41.445316]  v4l2_compat_ioctl32+0x21c/0x1420
>> [   41.449665]  __arm64_compat_sys_ioctl+0xc8/0x108
>> [   41.454273]  el0_svc_common.constprop.2+0xb0/0x168
>> [   41.459051]  do_el0_svc_compat+0x18/0x38
>> [   41.462964]  el0_sync_compat_handler+0x13c/0x194
>> [   41.467570]  el0_sync_compat+0x144/0x180
>> [   41.471483] Code: b9407802 eb02007f 540001e8 b9007404 (f81f8001)
>> [   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
>>>>>>>> instead
>>>>>>>> of adding check in queue setup.
>>>>>>>>
>>>>>>>>>> +
>>>>>>>>>> +     return 0;
>>>>>>>>>> +}

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