On 01/17/2017 10:59 PM, Nicolas Dufresne wrote:
Le mardi 17 janvier 2017 à 20:46 +0800, herman.chen@xxxxxxxxxxxxxx a
écrit :
If we move parser or part of DPB management mechanism into kernel we
will face a issue as follows:
One customer requires dpb management do a flush when stream occurs in
order to keep output frame clean.
While another one requires output frame with error to keep output
frame smooth.
And when only one field has a error one customer wants to do a simple
field copy to recover.
The driver should send all frames and simply mark the corrupted frames
using V4L2_BUF_FLAG_ERROR. This way, the userspace can then make their
own decision. It is also important to keep track and cleanup the
buffers meta's (which are application specific). If the driver silently
drops frame, it makes that management much harder.
About flushing and draining operation, they are respectively signalled
to the driver using STREAMOFF and CMD_STOP.
These are some operation related to strategy rather then mechanism.
I think it is not a good idea to bring such kind of flexible process
to kernel driver.
So here is the ultimate challenge that how to reasonably move the
parser and flexible process
which is encapsuled in firmware to a userspace - kernel stateless
driver model.
Moving the parsers in the kernel (on the main CPU) is not acceptable.
No, what is not what I said. What I want to do is "The whole plan in
userspace is just injecting a parsing operation and set those v4l2
control in kernel before enqueue a buffer into OUTPUT, which would keep
the most compatible with those stateful video IP(those with a firmware). "
This is too much of a security threat. Userspace should parse the data
into structures, doing any validation required before end.
My main question and that should have an impact decision, is if those
structures can be made generic. PDB handling is not that trivial (my
reference is VAAPI here, maybe they are doing it wrong) and with driver
specific structures, we would have this code copy-pasted over and over.
So with driver specific structures, it's probably better to keep all
the parsing and reordering logic outside (hence together).
The result to keep DPB and re-order inside the kernel is want
to be compatible with the original buffer operation.
Anyway the DPB structure could be common.
That remains, that some driver will deal with reordering on the
firmware side (even the if they don't parse), hence we need to take
this into consideration.
No sure what do you mean, I think all those driver with firmware
would do that.
regards,
Nicolas
Hello all:
I have recently finish the learning of the H.264 codec and ready to
write the driver. Although I have not get deep in syntax of H.264 but I
think I just need to reuse and extended the VA-API H264 Parser from
gstreamer. The whole plan in userspace is just injecting a parsing
operation and set those v4l2 control in kernel before enqueue a buffer
into OUTPUT, which would keep the most compatible with those stateful
video IP(those with a firmware).
But in order to do that, I can't avoid the management of DPB. I
decided to moving the DPB management job from userspace in kernel. Also
the video IP(On2 on rk3288 and the transition video IP on those future
SoC than rk3288, rkv don't have this problem) would a special way to
manage the DPB, which requests the same reference frame is storing in
the same reference index in the runtime(actually it is its Motion Vector
data appended in decoded YUV data would not be moved). I would suggest
to keep those job in kernel, the userspace just to need update the list0
and list1 of DPB. DPB is self managed in kernel the userspace don't need
to even dequeue the buffer from CAPTURE until the re-order is done.
The kernel driver would also re-order the CAPTURE buffer into display
order, and blocking the operation on CAPTURE until a buffer is ready to
place in the very display order. If I don't do that, I have to get the
buffer once it is decoded, and marking its result with the poc, I could
only begin the processing of the next frame only after those thing are
done. Which would effect the performance badly. That is what chromebook
did(I hear that from the other staff, I didn't get invoke in chromium
project yet). So I would suggest that doing the re-order job in kernel,
and inform the the userspace the buffers are ready when the new I
frame(key frame) is pushed into the video IP.
Although moving those job into kernel would increase the loading, but
I think it is worth to do that, but I don't know whether all those
thought are correct and high performance(It is more important than API
compatible especially for those 4K video). And I want to know more ideas
about this topic.
I would begin the writing the new driver after the coming culture new
year vacation(I would go to the Europe), I wish we can decide the final
mechanism before I begin this job.
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