On 4/14/2022 4:34 PM, Dmitry Baryshkov wrote:
On 15/04/2022 01:06, Kuogee Hsieh wrote:
On 4/8/2022 4:59 PM, Dmitry Baryshkov wrote:
On Fri, 8 Apr 2022 at 23:30, Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
wrote:
On 4/8/2022 5:27 AM, Dmitry Baryshkov wrote:
On 07/04/2022 00:28, Kuogee Hsieh wrote:
dp_hpd_plug_handle() is responsible for setting up main link and
send
uevent to notify user space framework to start video stream.
Similarly,
dp_hdp_unplug_handle is responsible to send uevent to notify user
space
framework to stop video stream and then tear down main link.
However there are rare cases, such as in the middle of system
suspending,
that uevent could not be delivered to user space framework.
Therefore
some kind of recover mechanism armed by timer need to be in place
in the
case of user space framework does not respond to uevent.
Hmm, how does userpsace 'respond' to the uevent? The driver should
send hotplug notifications to userspace, but it must not expect any
particular reaction. The userspace might be as simple, as fbdev
emulation, but the driver still should function correctly.
yes, driver is function correctly by setting up main link. but it does
not know which resolution to display.
It send hotplug notification through uevent to framework after main
link
is ready.
Framework is responsible to set up MDP timing engine to start
video stream.
However it does not know which
It's of no concern to the driver. It is completely the userspace
problem. After resuming, it should reread available video output
properties. The display could have been changed while the system is
suspended.
From your description I still do not understand why you need the
'recovery' mechanism.
I mean "recovery" means dp driver may leave stay at link ready
mistakenly after dongle unplugged due to missing framework action to
tear down main link so that next dongle plug in will not work.
Currently it was armed with timeout function and it will fired if
framework did not call msm_dp_display_disable() after 5 second.
framework = userspace?
Is my understanding correct? Currently DP driver sends a notification
to userspace that DP is unplugged, waits for userspace to disable DP
output, and only after that it will shutdown the link. Is this a
correct description?
Yes, you are correct, connection need to be tear down from top to bottom.
If so, then yes, your change is correct. I mean that the kernel
shouldn't wait for clients to stop using video pipeline if the sink
gets unplugged. Instead it should tear the video stream down and let
the DRM client cope with that.
I'm not sure how should the driver react if the client doesn't disable
the output, but then the sink gets reattached?
I do not know that either.
But it should not happen as long as framework response to uevent.
And a bit more interesting question: how should the driver behave if
the new sink is not compatible with the existing video stream.
When dongle plug/replug in, driver will always read sink's edid.
Therefore resolution database should be updated accordingly.
Anyway, we think this approach is not good. therefore it is replaced
with below patch.
drm/msm/dp: tear down main link at unplug handle immediately
