On 5/16/2023 4:20 PM, Dmitry Baryshkov wrote:
On 17/05/2023 01:35, Abhinav Kumar wrote:
On 5/16/2023 6:50 AM, Dmitry Baryshkov wrote:
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.
Let me clarify / correct the response. Ideally thats what is usually
done to wait for disconnect when we get connect and vice-versa. HDMI
still does it the same way.
https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/msm/hdmi/hdmi_hpd.c#L196
So, HDMI HPD is real flip-flop, sounds fine.
But I checked with kuogee that DP always enabled HPD connect and
disconnect interrupts by default and he mentioned its mainly because
we wanted to enable HPD connect / disconnect by default but not the
others.
That being said, the logic is close to flip-flop that when you get a
connect event, you wait for the "other" interrupts which are possible
which is IRQ_HPD and REPLUG and during disconnect, those are not
possible so disable them. Thats why the calls to
dp_catalog_hpd_config_intr() are present in the plug_handle /
unplug_handle to enable the "other possible" interrupts.
Can we keep them always enabled? Are these interrupts edge-triggered
or level-triggered? What prevents us from enabling these interrupts
all the time? Or enabling all 4 interrupts in hpd_enable() and
disabling them in hpd_disable()? Can IRQ_HPD or REPLUG fire when the
cable is disconnected?
1) edge-trigger at hpd pin low. However hpd block will start
debouncing logic and set status bit (plug, unplug, hpd_irq ore replug)
properly base on the result of debunce.
2) there should be fine to have all interrupts enabled
3) IRQ_HPD and REPLUG will not happen when disconnected.
The logic from dp_display_config_hpd() is getting removed in this
patch, in case you didnt check to align just with hpd_enable /
hpd_disable callbacks.
I saw this. The code is being moved to dp_bridge_hpd_enable(), as I
mentioned in the email.
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?
Yes, this should be possible but we would like to test this. But what
about the interrupt masks then. So you are saying, hpd_enable will
only toggle the DP_DP_HPD_CTRL_HPD_EN but leave the HPD connect and
disconnect interrupts intact? That also doesnt sound right.
enabling the block all the time and then toggling the interrupt masks
seemed like a better thing.
Why? We do not need the block outside of the
hpd_enable()/hpd_disable() pair. Even from the power consumption
perspective, disabling the unused block sounds better to me.
We are mean within the block of hpd_enabled and hdp_disabled pair,
At hpd_enabled, we will do both item 1) and 2) instead of just only item
1) as you mentioned. you still need power on hpd block to just do item2).
1) enabled DP_DP_HPD_CTRL_HPD_EN
2) enable HDP interrupts (plug, unplug, hpd_irq and replug)
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()".
Yes, we are aware of it and this patch keeps that documented
expectation intact. AFAICT, we want to skip dp_bridge_hpd_notify in
the internal hpd case. Please note, like I wrote before, these
callbacks are listed as optional
632 * This callback is optional and shall only be implemented by
bridges
633 * that support hot-plug notification without polling.
Bridges that
634 * implement it shall also implement the @hpd_disable
callback and set
635 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
636 */
637 void (*hpd_enable)(struct drm_bridge *bridge);
638
So, the intention of introducing them to DP driver was to handle the
case which Bjorn listed. Otherwise things are fine the way it is
because like Stephen wrote, whether to use internal_hpd or not is a
probe time decision, we really dont need to tie it with
hpd_enable/hpd_disable callbacks.
Small correction correct. This is not a probe-time decision. One can
not decide this just basing on the next bridge existence.
drm_bridge_connector decides which bridges to use for HPD or DETECT at
the drm_bridge_connector_init(), which happens duing dpu_kms_hw_init().
hpd_enable/disable are optional (the drm core can function without
them being provided). However having them implemented is still useful.
It allows one to disable unused logic.
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.
Sure, but questioning why it exists and that it can be removed
distracts folks from the objective of fixing the hpd issue.
I have some questions about your assessment of uevents not being sent
to userspace . Answers below to that.
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
This list is correct except for the other aspect I explained.
Like you mentioned, we really need to power up the hpd block only
when hpd_enable is called. But to power up the hpd block, we need:
-> AUX clk
-> mdss ahb clk
-> program hpd registers
We need to carefully isolate these out to hpd_enable / hpd_disable.
This can be tried but will only delay this fix longer ... We can give
it a shot.
I'd start with the simpler approach. We have AUX and MDSS AHB clocks
enabled all the time. I'm suggesting to limit (for the fix)
hpd_enable()/disable() to HPD register programming, if that is easier
ATM. Power optimizations can come later, provided everybody
understands them. If AUX or AHB clocks programming is easy, them I'm
fine with them getting in at the same time.
All these concerns should have been thought of when actually
introducing the internal_hpd flag and the hpd_enable / hpd_disable
callbacks. But looks like neither sides did.
Yes. Quite unfortunate, but true.
Anyway, like we always do, we can attempt cleaning this up like the
way i have explained above to move the enable / disable of those 3
resources to hpd_enable / hpd_disable. Hopefully it works and is a
small change.
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.
Thanks for confirming.
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
pm_runtime status is really not affected with this patch.
Even without this patch, the dp_display_host_deinit was called
dp_pm_suspend which would have powered down the HPD related resources.
hpd_enable / hpd_disable callbacks from the DRM fwk only provide us
another hook to do something which was already being done.
There was a point from Bjorn that there is no need to power on the DP
block, if the output is disabled and HPD is not enabled. It was not
directly related to this patch, but (in my opinion) it was an attempt
to understand and optimize the logic.
HPD notifications explained below.
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.
Today the DP driver calls drm_helper_hpd_irq_event to notify events
which calls drm_kms_helper_hotplug_event internally. So what part is
missing?
Ack, I missed this call beneath all the event processing.
However it still misses a call to drm_bridge_connector_hpd_notify() to
notify all the bridges in a chain. This might become important later
for the redrivers.
Not to mention that drm_helper_hpd_irq_event() loops all connectors to
check which ones were changed. For DP driver this is not required. We
already know the exact connector and new state, so the loop is
unnecessary.
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.
I am seeing this from users in drm/bridge (that is external hpd)
which makes sense. So if I understand this better, in external_hpd
case I do see its purpose as this info has to be passed down from the
bridge to the Display controller through the drm fwk, not for the
internal_hpd case because in that case the controller already knows
as it is the one generating this interrupt.
With the help of drm_bridge_hpd_notify() and proper hpd_notify() we
can unify both cases. The driver just gets the
connected/disconnected/attention events and handles them. It should
not matter, which part generates them.
- 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.
