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
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.
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.
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.
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.
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.
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.
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.
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?
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.
- 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.
