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Date: Mon, 11 Sep 2017 13:03:41 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Gustavo Padovan <gustavo@...ovan.org>, linux-media@...r.kernel.org
Cc: Mauro Carvalho Chehab <mchehab@....samsung.com>,
Shuah Khan <shuahkh@....samsung.com>,
linux-kernel@...r.kernel.org,
Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [PATCH v3 02/15] [media] vb2: add explicit fence user API
On 09/11/2017 12:55 PM, Hans Verkuil wrote:
> On 09/07/2017 08:42 PM, Gustavo Padovan wrote:
>> From: Gustavo Padovan <gustavo.padovan@...labora.com>
>>
>> Turn the reserved2 field into fence_fd that we will use to send
>> an in-fence to the kernel and return an out-fence from the kernel to
>> userspace.
>>
>> Two new flags were added, V4L2_BUF_FLAG_IN_FENCE, that should be used
>> when sending a fence to the kernel to be waited on, and
>> V4L2_BUF_FLAG_OUT_FENCE, to ask the kernel to give back an out-fence.
>>
>> v2: add documentation
>>
>> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
>> ---
>> Documentation/media/uapi/v4l/buffer.rst | 19 +++++++++++++++++++
>> drivers/media/usb/cpia2/cpia2_v4l.c | 2 +-
>> drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 ++--
>> drivers/media/v4l2-core/videobuf2-v4l2.c | 2 +-
>> include/uapi/linux/videodev2.h | 4 +++-
>> 5 files changed, 26 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
>> index ae6ee73f151c..664507ad06c6 100644
>> --- a/Documentation/media/uapi/v4l/buffer.rst
>> +++ b/Documentation/media/uapi/v4l/buffer.rst
>> @@ -648,6 +648,25 @@ Buffer Flags
>> - Start Of Exposure. The buffer timestamp has been taken when the
>> exposure of the frame has begun. This is only valid for the
>> ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type.
>> + * .. _`V4L2-BUF-FLAG-IN-FENCE`:
>> +
>> + - ``V4L2_BUF_FLAG_IN_FENCE``
>> + - 0x00200000
>> + - Ask V4L2 to wait on fence passed in ``fence_fd`` field. The buffer
>> + won't be queued to the driver until the fence signals.
>> +
>> + * .. _`V4L2-BUF-FLAG-OUT-FENCE`:
>> +
>> + - ``V4L2_BUF_FLAG_OUT_FENCE``
>> + - 0x00400000
>> + - Request a fence for the next buffer to be queued to V4L2 driver.
>> + The fence received back through the ``fence_fd`` field doesn't
>> + necessarily relate to the current buffer in the
>> + :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` ioctl. Although, most of the time
>> + the fence will relate to the current buffer it can't be guaranteed.
>> + So to tell userspace which buffer is associated to the out_fence,
>> + one should listen for the ``V4L2_EVENT_BUF_QUEUED`` event that
>> + provide the id of the buffer when it is queued to the V4L2 driver.
>
> As mentioned in the previous patch, this flag should just signal that userspace
> wants to receive a BUF_QUEUED event with the out-fence for this buffer. It's up
> to the driver to ensure the correct ordering of the events.
I'll wait for v4 before continuing my review.
Hans
>
> I'm missing documentation for the new fence_fd field.
>
> It should mention that fence_fd is ignored if the IN_FENCE isn't set. Applications
> will set fence_fd (aka reserved2) to 0, which should be fine as long as IN_FENCE
> isn't set.
>
>>
>>
>>
>> diff --git a/drivers/media/usb/cpia2/cpia2_v4l.c b/drivers/media/usb/cpia2/cpia2_v4l.c
>> index 3dedd83f0b19..6cde686bf44c 100644
>> --- a/drivers/media/usb/cpia2/cpia2_v4l.c
>> +++ b/drivers/media/usb/cpia2/cpia2_v4l.c
>> @@ -948,7 +948,7 @@ static int cpia2_dqbuf(struct file *file, void *fh, struct v4l2_buffer *buf)
>> buf->sequence = cam->buffers[buf->index].seq;
>> buf->m.offset = cam->buffers[buf->index].data - cam->frame_buffer;
>> buf->length = cam->frame_size;
>> - buf->reserved2 = 0;
>> + buf->fence_fd = -1;
>> buf->reserved = 0;
>> memset(&buf->timecode, 0, sizeof(buf->timecode));
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
>> index 821f2aa299ae..d624fb5df130 100644
>> --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
>> +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
>> @@ -370,7 +370,7 @@ struct v4l2_buffer32 {
>> __s32 fd;
>> } m;
>> __u32 length;
>> - __u32 reserved2;
>> + __s32 fence_fd;
>> __u32 reserved;
>> };
>>
>> @@ -533,8 +533,8 @@ static int put_v4l2_buffer32(struct v4l2_buffer *kp, struct v4l2_buffer32 __user
>> put_user(kp->timestamp.tv_usec, &up->timestamp.tv_usec) ||
>> copy_to_user(&up->timecode, &kp->timecode, sizeof(struct v4l2_timecode)) ||
>> put_user(kp->sequence, &up->sequence) ||
>> - put_user(kp->reserved2, &up->reserved2) ||
>> put_user(kp->reserved, &up->reserved) ||
>> + put_user(kp->fence_fd, &up->fence_fd) ||
>
> Could you move this up one line? It's easier to parse this diff if it is clear
> that fence_fd replaced reserved2.
>
>> put_user(kp->length, &up->length))
>> return -EFAULT;
>>
>> diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
>> index 0c0669976bdc..110fb45fef6f 100644
>> --- a/drivers/media/v4l2-core/videobuf2-v4l2.c
>> +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
>> @@ -203,7 +203,7 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
>> b->timestamp = ns_to_timeval(vb->timestamp);
>> b->timecode = vbuf->timecode;
>> b->sequence = vbuf->sequence;
>> - b->reserved2 = 0;
>> + b->fence_fd = -1;
>> b->reserved = 0;
>>
>> if (q->is_multiplanar) {
>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>> index 185d6a0acc06..e5abab9a908c 100644
>> --- a/include/uapi/linux/videodev2.h
>> +++ b/include/uapi/linux/videodev2.h
>> @@ -924,7 +924,7 @@ struct v4l2_buffer {
>> __s32 fd;
>> } m;
>> __u32 length;
>> - __u32 reserved2;
>> + __s32 fence_fd;
>> __u32 reserved;
>> };
>>
>> @@ -961,6 +961,8 @@ struct v4l2_buffer {
>> #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE 0x00010000
>> /* mem2mem encoder/decoder */
>> #define V4L2_BUF_FLAG_LAST 0x00100000
>> +#define V4L2_BUF_FLAG_IN_FENCE 0x00200000
>> +#define V4L2_BUF_FLAG_OUT_FENCE 0x00400000
>>
>> /**
>> * struct v4l2_exportbuffer - export of video buffer as DMABUF file descriptor
>>
>
> Regards,
>
> Hans
>
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