On 5/2/20 10:04 AM, Sowjanya Komatineni wrote:
On 5/2/20 9:55 AM, Sowjanya Komatineni wrote:
On 5/2/20 9:14 AM, Sowjanya Komatineni wrote:
On 5/2/20 9:03 AM, Sowjanya Komatineni wrote:
On 5/2/20 8:38 AM, Sowjanya Komatineni wrote:
On 5/2/20 8:16 AM, Dmitry Osipenko wrote:
02.05.2020 06:55, Sowjanya Komatineni пишет:
On 5/1/20 8:39 PM, Sowjanya Komatineni wrote:
On 5/1/20 2:05 PM, Sowjanya Komatineni wrote:
On 5/1/20 1:58 PM, Sowjanya Komatineni wrote:
On 5/1/20 1:44 PM, Sowjanya Komatineni wrote:
On 5/1/20 11:03 AM, Sowjanya Komatineni wrote:
On 4/30/20 4:33 PM, Sowjanya Komatineni wrote:
On 4/30/20 4:14 PM, Sowjanya Komatineni wrote:
And in this case synchronization between start/finish
threads should be
needed in regards to freezing.
Was thinking to have counter to track outstanding frame
w.r.t single shot issue b/w start and finish and
allow to
freeze only when no outstanding frames in process.
This will make sure freeze will not happen when any
buffers
are in progress
Note that this could be a wrong assumption, I'm not
closely familiar
with how freezer works.
kthread_start can unconditionally allow try_to_freeze
before
start of frame capture
We can compute captures inflight w.r.t single shot
issued
during capture start and finished frames by
kthread_finish
and allow kthread_finish to freeze only when captures
inflight is 0.
This allows freeze to happen b/w frames but not in
middle of
frame
will have caps inflight check in v12 to allow freeze finish
thread only when no captures are in progress
try_to_freeze() returns thread frozen state and looks
like we
can use this in kthread finish to allow finish thread to
freeze
only when kthread_start is already frozen and no buffers in
progress/initiated for capture.
chan->capture_frozen holds frozen state returned from
try_to_freeze() in start kthread
chan->capture_reqs increments after every single shot issued.
static int chan_capture_kthread_finish(void *data)
{
struct tegra_vi_channel *chan = data;
struct tegra_channel_buffer *buf;
int caps_inflight;
set_freezable();
while (1) {
wait_event_interruptible(chan->done_wait,
!list_empty(&chan->done) ||
kthread_should_stop());
/* dequeue buffers and finish capture */
buf = dequeue_buf_done(chan);
while (buf) {
tegra_channel_capture_done(chan, buf);
buf = dequeue_buf_done(chan);
}
if (kthread_should_stop())
break;
caps_inflight = chan->capture_reqs - chan->sequence;
if (chan->capture_frozen && !caps_inflight)
try_to_freeze();
}
return 0;
}
Freezing happens prior to suspend() during suspend entry
and when
we implement suspend/resume during suspend we stop
streaming where
we stop threads anyway.
So, was thinking why we need these threads freezable here?
Hi Dmitry,
Did some testing and below are latest observation and fix I
tested.
wait_event_interruptible() uses schedule() which blocks the
freezer.
When I do suspend while keeping streaming active in
background, I
see freezing of these threads fail and call trace shows
__schedule
-> __switch_to from these kthreads.
wait_event_freezable() uses freezable_schedule() which
should not
block the freezer but we can't use this here as we need
conditional
try_to_freeze().
So, doing below sequence works where we set PF_FREEZER_SKIP
flag
thru freezer_not_count() before wait_event which calls
schedule()
and remove PF_FREEZER_SKIP after schedule allows
try_to_freeze to
work and also conditional try_to_freeze below prevents freezing
thread in middle of capture.
while (1) {
freezer_not_count()
wait_event_interruptible()
freezer_count()
...
...
if (chan->capture_frozen && !caps_inflight)
try_to_freeze()
}
Please comment if you agree with above sequence. Will
include this
in v12.
sorry, freezer_count() does try_to_freeze after clearing skip
flag.
So, dont think we can use this as we need conditional
try_to_freeze.
Please ignore above sequence.
Or probably we can take closer look on this later when we add
suspend/resume support as it need more testing as well.
As this is initial series which has TPG only I think we
shouldn't
get blocked on this now. Series-2 and 3 will be for sensor
support
and on next series when we add suspend/resume will look into
this.
When freeze activity starts and in case if finish thread
freezes prior
to start thread issuing capture, its the VI hardware writes
data to
the allocated buffer address.
finish thread just checks for the event from the hardware and
we don't
handle/process directly on memory in this driver.
So even we freeze done thread when single shot is issued frame
buffer
gets updated.
In case if capture thread is frozen there will not buffers
queued to
process by finish thread. So, this will not be an issue.
So, probably we don't need to do conditional try_to_freeze and
what we
have should work good in this corner case.
I still need to change wait_event_interruptible() to
wait_event_freezable() but no need to synchronize finish thread
freeze
with start thread as even on issuing capture start its vi
hardware that
does frame buffer update and finish thread just checks for
mw_ack event
and returns buffer to application.
The problem we are primarily trying to avoid is to have
suspending being
done in the middle of IO.
IIUC, even if system will be suspended in the middle of VI IO, it
won't
be fatal. In worst case the buffer capture should fail on resume
from
suspend. Could you please try to simulate this potential issue
and see
what result will be on suspending in the middle of VI IO?
We don't want to suspend system / stop streaming in the middle of
IO, so
this problem of a proper threads tear-down still exists. It should
become easier to resolve the problem in a case of a proper
suspending
callback because the "start" thread could be turned down at any
time, so
it should be easier to maintain a proper tear-down order when
threads
are fully controlled by the driver, i.e. the "start" thread goes
down
first and the "finish" is second, blocking until the capture is
completed.
I don't see issue of tear-down threads in case of suspend as we do
stop streaming where thread stop happens on both threads and are
stopped only after processing all outstanding buffers.
Regarding freezing activity during suspend, If done thread freezes
prior to processing buffers for finish, vi hardware is still active
by this time which will update the frame buffer for initiated
capture. Driver is not directly involved in this frame buffer update.
Finish thread only checks for completion to return buffers back to
the application when done.
when done thread freeze happens after start thread initiated
capture, vi hardware continues to update frame buffer for ongoing
capture till it hits driver suspend callback. Yes worst case this
frame data may not be valid data if invoking of this driver suspend
happens immediate after this thread freeze during system suspend.
But driver will still hold buffers to return which will be returned
back on resume when threads are out from frozen state.
Also stop stream ioctl request happens during suspend where both
threads will be stopped properly. done thread stop happens only after
finishing all outstanding buffers.
Stop stream request happens from streaming applications so even
without driver suspend/resume implementation currently, streaming
will be stopped prior to system suspend where both threads will be
stopped properly (after finishing out standing buffers) and will be
resumed by application on system resume
Also tested suspending while streaming with this unconditional
freeze, I don't see any issue as application stops stream where
v4l_streamoff gets executed during suspend and on resume streaming
starts where v4l_streamon happens.
So, I don't see any issue with existing implementation of
unconditional freeze.
To be more clear,
suspend while streaming use case...
- start thread initiating capture
- done thread frozen (with outstanding buffers in process but vi
hardware still continues to update frame buffer)
- start thread frozen
application holding video device will issue stream off ioctl
- stop_streaming does kthread_stop
- threads wake up and start thread breaks and finish thread breaks
after checking outstanding buffers and returning to application
- vi/csi power/clocks off
on resume, application starts streaming again where fresh start stream
happens.
I think yours suggestion about dropping the freezing from the
threads
for now and returning back to it later on (once a proper
suspend/resume
support will be added) sounds reasonable.
But if you'd want to keep the freezing, then the easy solution
could be
like that:
1. "start" thread could freeze at any time
2. "finish" thread could freeze only when the "start" thread
is frozen
and capture isn't in-progress. Use frozen(kthread_start_capture) to
check the freezing state.
https://elixir.bootlin.com/linux/v5.7-rc3/source/include/linux/freezer.h#L25
That's exactly what I tried, below is the snippet.
But as mentioned I am seeing freezing fail when I
wait_event_interruptible() in either of the threads.
60.368709] Call trace:
[ 60.371216] __switch_to+0xec/0x140
[ 60.374768] __schedule+0x32c/0x668
[ 60.378315] schedule+0x78/0x118
[ 60.381606] chan_capture_kthread_finish+0x244/0x2a0 [tegra_video]
[ 60.387865] kthread+0x124/0x150
[ 60.391150] ret_from_fork+0x10/0x1c
wait_event_interruptible() API uses schedule() which blocks
freezer while wait_event_freezable APIs uses freezable_schedule()
which allows to skip freezer during schedule and then clears skip
and calls try_to_freeze()
But we can't use wait_event_freezable() here as we need
conditional freeze.
while (1) {
caps_inflight = chan->capture_reqs - chan->sequence;
if (frozen(chan->kthread_start_capture) && !caps_inflight)
wait_event_freezable(chan->done_wait,
!list_empty(&chan->done) ||
kthread_should_stop());
else
wait_event_interruptible(chan->done_wait,
!list_empty(&chan->done) ||
kthread_should_stop());
/* dequeue buffers and finish capture */
...
...
if (kthread_should_stop())
break;
}
Below works if I skip freezer during wait_event_interruptible as we
can't use wait_event_freezable when we need conditional try_to_freeze()
But I am not sure if this is allowed to do this explicit PF_FREEZER_SKIP
clear.
Also, as explained above I don't even think we need conditional
try_to_freeze() as v4l2 ioctl stream off gets called during closing of
device node when suspend happens and before stopping threads outstanding
buffers are returned properly. So, I don't see any issue with
unconditional try_to_freeze()
while (1) {
/* allow to freeze only when no captures in progress */
caps_inflight = chan->capture_reqs - chan->sequence;
if (frozen(chan->kthread_start_capture) && !caps_inflight) {
wait_event_freezable(chan->done_wait,
!list_empty(&chan->done) ||
kthread_should_stop());
} else {
/*
* Skip freeze during wait_event_interruptible as
* schedule() blocks freezer.
*/
if (freezing(current))
freezer_do_not_count();
wait_event_interruptible(chan->done_wait,
!list_empty(&chan->done) ||
kthread_should_stop());
if (freezing(current))
current->flags &= ~PF_FREEZER_SKIP;
}
/* dequeue buffers and finish capture */
...
...
if (kthread_should_stop())
break;
}
