On 13/05/2023 00:28, Abhinav Kumar wrote:
Hi Bjorn and Dmitry
On 5/12/2023 12:34 PM, Kuogee Hsieh wrote:
On 5/12/2023 10:28 AM, Dmitry Baryshkov wrote:
On Fri, 12 May 2023 at 19:52, Kuogee Hsieh <quic_khs...@quicinc.com>
wrote:
On 5/11/2023 5:54 PM, Dmitry Baryshkov wrote:
On Fri, 12 May 2023 at 03:16, Kuogee Hsieh
<quic_khs...@quicinc.com> wrote:
On 5/11/2023 8:57 AM, Dmitry Baryshkov wrote:
On 11/05/2023 18:53, Bjorn Andersson wrote:
On Thu, May 11, 2023 at 07:24:46AM +0300, Dmitry Baryshkov wrote:
On Wed, 10 May 2023 at 23:31, Kuogee Hsieh
<quic_khs...@quicinc.com>
wrote:
The internal_hpd flag was introduced to handle external DP HPD
derived from GPIO
pinmuxed into DP controller. HPD plug/unplug interrupts cannot be
enabled until
internal_hpd flag is set to true.
At both bootup and resume time, the DP driver will enable
external DP
plugin interrupts and handle plugin interrupt accordingly.
Unfortunately
dp_bridge_hpd_enable() bridge ops function was called to set
internal_hpd
flag to true later than where DP driver expected during bootup
time.
This causes external DP plugin event to not get detected and
display stays blank.
Move enabling HDP plugin/unplugged interrupts to
dp_bridge_hpd_enable()/disable() to
set internal_hpd to true along with enabling HPD plugin/unplugged
interrupts
simultaneously to avoid timing issue during bootup and resume.
Fixes: cd198caddea7 ("drm/msm/dp: Rely on hpd_enable/disable
callbacks")
Signed-off-by: Kuogee Hsieh <quic_khs...@quicinc.com>
Thanks for debugging this!
However after looking at the driver I think there is more than
this.
We have several other places gated on internal_hpd flag, where
we do
not have a strict ordering of events.
I see that dp_hpd_plug_handle() and dp_hpd_unplug_handle() also
toggle
DP_DP_IRQ_HPD_INT_MASK and DP_DP_HPD_REPLUG_INT_MASK depending on
internal_hpd. Can we toggle all 4 interrupts from the
hpd_enable/hpd_disable functions? If we can do it, then I think
we can
drop the internal_hpd flag completely.
No we cannot. The HPD logic works in a flip-flop model. When we get the
plug interrupt, we need to flip to tell the hw to wait for unplug and
when we get unplug, we need to tell the hw to wait for plug.
But, doesn't dp_display_config_hpd() (current code) or
dp_bridge_hpd_enable() (after this patch) enable both plug and unplug
interrupts? This doesn't fit well into the flip-flop description.
The two calls in plug_handle() / unplug_handle() are doing that whereas
hpd_enable/hpd_disable are disabling the hpd interrupts altogether.
In other words, we cannot rely on hpd_enable() / hpd_disable() calls to
do the flip part as that has to be done every plug/unplug. In addition
we need to handle the compliance test cases with REPLUG.
Thank you for the explanation. Would it be possible to keep mask/unmask,
but make hpd_enable/hpd_disable toggle DP_DP_HPD_CTRL_HPD_EN instead?
So hpd_enable / hpd_disable is not the right place to move all these calls.
Yes, that's what I believe the DRM framework intend us to do.
The problem, and reason why I didn't do tat in my series, was
that in
order to update the INT_MASKs you need to clock the IP-block and
that's
done elsewhere.
So, for the internal_hpd case, it seems appropriate to
pm_runtime_get()
in hpd_enable() and unmask the HPD interrupts, and mask the
interrupts
and pm_runtime_put() in hpd_disable().
I dont agree completely on this. The blocks powering the HPD block also
power other things. So the AUX clk and host_init() both are needed for
HPD but they power not just the HPD.
So powering all of these at hpd_enable / hpd_disable would be an
overkill for that call and not required as well.
The main requirement behind hpd_enable/disable is that:
- hpd_enable makes sure that hpd events are properly detected and
delivered afterwards.
- hpd_disable must unroll this. In other words, "Once [..hpd_disable..]
returns the bridge shall not call drm_bridge_hpd_notify()".
Before talking about removing hpd_event_thread, I think we should
understand why its there. It handles all asynchronous connection and
sink related events in one centralized place like
connect/disconnect/irq_hpd.
This is a well tested code with multiple dongles on chromebooks and I
dont see any alternative to it at the moment and dont think that
discussion is necessary in the context of this bug fix . We can talk
about it more in one of our sync ups if you want to know more.
Sync ups are private. Can we please keep this discussion public? It
would be beneficial for other parties too (e.g. ChromeOS people).
The main issue with the current event thread is that it short cuts all
HPD handling. This causes some uevents not being sent to the userspace, etc.
Please see below.
Based on the responses I have seen so far, I see that we had to
introduce the dynamic control of internal_hpd for below case :
2) DP without GPIO: Downstream drm_bridge connected, is_edp = false and
internal HPD-logic should not be used/enabled (internal_hpd = false).
Power doesn't need to be on unless hpd_notify is invoked to tell us that
there's something connected...
Ideally, the DP block should be in the runtime suspension state, unless
one of the following happens:
- hpd_enable() was called without consequent hpd_disable() call
- atomic_pre_enable() was called to start up the stream,
atomic_post_disable() was not called yet
- get_edid() / get_modes() is in progress
- detect() is in progress
- eDP? I admit I do not fully understand the requirements there, so
Stephen / Doug might be in a better position to comment about it
So we want internal_hpd to be false for this case.
That is good information and provides the context of why hpd_enable /
hpd_disable callbacks were implemented as they are optional as per the
framework.
I saw Bjorn mentioned that "The DRM framework will invoke hpd_enable on
the bridge furthest out that
has OP_HPD. So in the case of HPD signal being pinmuxed into the
HPD-logic, dp_bridge_hpd_enable() will be invoked.
"
For my understanding, this logic is in the drm_bridge_connector_init()
right? So bridge_connector->bridge_detect will hold the last bridge and
hence enable_hpd / disable/hpd gets called only for the last one right?
You are mixing bridge_detect and bridge_hpd here. But yes, these
pointers are initialized to the last bridges implementing
correspondingly OP_DETECT / OP_HPD. Then drm_bridge_connector_detect()
will call bridge_detect->detect(). drm_bridge_connector_enable_hpd()
will call bridge_hpd->hpd_enable.
Note, the hpd_notify() callback will be called for all bridges in a chanin.
If all this is correct, I think the fix posted at the moment is the best
possible one as it correctly does what hpd_enable / hpd_disable
callbacks are supposed to do without overdoing it.
What are the concerns with this patch with all the explanation I have
given now.
I'd like to better understand the flip-flop story and the
DP_DP_HPD_CTRL_HPD_EN.
Also, as you can see, the discussion of this patch popped up discussions
for two other problems:
- power consumption / pm_runtime status
- HPD notifications
But for edp and external HPD-signal we also need to make sure
power is
on while something is connected...
I think this is already handled by the existing code, see calls
to the
dp_display_host_init().
I went on and checked other places where it is used:
- dp_hpd_unplug_handle(), guarding DP_DP_HPD_PLUG_INT_MASK
toggling. I
think we can drop these two calls completely. The function is
under
the event_mutex protection, so other events can not interfere.
- dp_bridge_hpd_notify(). What is the point of this check? If some
other party informs us of the HPD event, we'd better handle it
instead
of dropping it. Correct? In other words, I'd prefer seeing the
hpd_event_thread removal. Instead of that I think that on
HPD/plug/unplug/etc. IRQ the driver should call into the drm
stack,
then the hpd_notify call should process those events.
Now about the hpd_event_thread and the callbacks.
Currently the driver shortcuts the DRM infrastructure and tries to
handle all the details / call sequences. This might be partially
correct, but it definitely needs to be improved:
drm_bridge_connector_hpd_cb() also calls drm_kms_helper_hotplug_event(),
which does other imporant things like sending uevent, notifying drm
clients, etc. This part is completely missing for the internal_hpd case
in the current driver.
Thus I suggest the following refactoring:
- On all HPD events the driver should call drm_bridge_hpd_notify(). For
the REPLUG it might be required to perform two notifications in a sequence.
- drm_bridge_connector_hpd_cb() should be taught to pass through the
(old_status == status) events (either in all cases or if the driver
requests that)
- The dp_bridge_hpd_notify() will be called for all HPD events. This way
it becomes natural to remove the !internal_hpd check from this function
and handle all HPD events from the proper single place, hpd_notify.
1) DP with GPIO: No downstream drm_bridge are connected, is_edp =
false
and internal HPD-logic is in used (internal_hpd = true). Power
needs to
be on at all times etc.
2) DP without GPIO: Downstream drm_bridge connected, is_edp =
false and
internal HPD-logic should not be used/enabled (internal_hpd = false).
Power doesn't need to be on unless hpd_notify is invoked to tell
us that
there's something connected...
- dp_bridge_hpd_notify(). What is the point of this check? <== i have
below two questions,
1) can you explain when/what this dp_bridge_hpd_notify() will be
called?
The call chain is drm_bridge_hpd_notify() ->
drm_bridge_connector_hpd_notify() -> .hpd_notify() for all drm_bridge
in chain
One should add a call to drm_bridge_hpd_notify() when the hotplug
event has been detected.
Also please note the patch
https://patchwork.freedesktop.org/patch/484432/
2) is dp_bridge_hpd_notify() only will be called at above case #2?
and
it will not be used by case #1?
Once the driver calls drm_bridge_hpd_notify() in the hpd path, the
hpd_notify callbacks will be called in case#1 too.
BTW: I don't see drm_bridge_hpd_notify() or
drm_kms_{,connector_}_hotplug_event() HPD notifications in the DP
driver at all. This should be fixed.
Just curious, since dp_bridge_detect() only return either
connector_status_connected or connector_status_disconnect,
how IRQ_HPD_INT (attention) and HPD_REPLUG_INT be generated at DP
case#1?
if (bridge.status == connected && status == connected) {
either attention or replug were reported
}
BTW: what is HPD_REPLUG_INT, if you excuse my ignorance?
HPD high -- drop to low for less than 2 ms -- go back to high again
Currently, we have to treat this scenario as HPD_UNPLUG_int followed
by HPD_PLUG_INT to pass compliance test
I agree, that seems to be what's expected of us from the DRM
framework.
--
With best wishes
Dmitry
