On 7/11/22 11:13, Liviu Dudau wrote:
On Fri, Jul 08, 2022 at 07:03:37PM +0100, Carsten Haitzler wrote:
On 7/8/22 17:02, Liviu Dudau wrote:
On Mon, Jun 06, 2022 at 12:47:14PM +0100, carsten.haitzler@xxxxxxxxxxxx wrote:
From: Carsten Haitzler <carsten.haitzler@xxxxxxx>
Hi Carsten,
Sometimes there is an extra dcm crtc state in the pipeline whose
penting vblank event has not been handled yet. We would previously
throw this out and the vblank event never triggers leading to hard
lockups higher up the stack where an expected vlank event never comes
back (screen freezes).
This fixes that by tracking a pending crtc state that needs handling
and handle it producing a vlank event next vblank if it had not
laready been handled before. This fixes the hangs and ensures our
display keeps updating seamlessly and is certainly a much better state
to be in than after some time ending up with a mysteriously frozen
screen and a lot of kernle messages complaining about this too.
Sorry it took me so long to review and reply to this patch, but I had this nagging
No worries. :)
feeling that the patch is not actually correct so I've tried to track the actual
issue. It turns out that the problem is easy to reproduce in a different setup with
Mali D71 and it comes from the fact that Komeda doesn't properly wait for the
hardware to signal acceptance of config valid on setting new commits. I have created
a new patch that I would be happy if you can test to try to fix the actual issue.
This works (tested).
Thank you very much for testing this! Can I add your Tested-by?
Indeed. Go for it.
One errant "flip without commit":
[ 9.402559] fbcon: Taking over console
[ 9.525373] [drm:komeda_print_events [komeda]] *ERROR* err detect: gcu:
MERR, pipes[0]: FLIP, pipes[1]: None
[ 9.525455] [drm] CRTC[0]: FLIP happened but no pending commit.
[ 9.542215] Console: switching to colour frame buffer device 240x67
Is this with your 2/3 patch applied and coming out from the firmware having already
initialised the hardware? If so, the handover probably doesn't quiescence the
interrupts correctly so an interrupt is pending when the kernel driver is
initialised. That's another area worth looking at for the handover purposes.
Yeah. the firmware is not doing a very clean handover - it's leaving the
hardware in whatever state it has. it probably could shut down
interrupts on handover, but not something to worry about in the kernel
driver at this point.
But nothing worrying. It does work, though doesn't compile due to:
drivers/gpu/drm/arm/display/komeda/komeda_kms.c: In function
‘komeda_kms_atomic_commit_hw_done’:
drivers/gpu/drm/arm/display/komeda/komeda_kms.c:77:9: error: ‘for’ loop
initial declarations are only allowed in C99 or C11 mode
77 | for (int i = 0; i < kms->n_crtcs; i++) {
| ^~~
drivers/gpu/drm/arm/display/komeda/komeda_kms.c:77:9: note: use option
‘-std=c9
’, ‘-std=gnu99’, ‘-std=c11’ or ‘-std=gnu11’ to compile your code
but that was a trivial fixup.
Interesting that I'm not seeing that, probably due to using GCC12? Anyway, I'll fix
that and send a proper patch.
I tend to use newer gcc's indeed, but I am using gcc11 in this case.
Your commit handler does sit and wait. I guess I avoided that and had it
still deferred and handled next time the vblank interrupt fires. Yours is a
bit shorter and less complex so it wins. :)
Yes, that's the essence of my issue with your patch. Delaying the handling of the
event until the next vblank means older software that doesn't use the timestamping
from the vblank event will get wrong framerates (playing video might be affected).
But this is a rare situation. I certainly was very happy going from "my
entire display locks up and only a reboot really fixes it" to "look ma -
it works and I didn't even see a stuttered frame!" :) But your fix is
better in that regard.
Waiting here when we're also calling drm_atomic_helper_wait_for_flip_done() after
drm_atomic_helper_commit_hw_done() feels wrong, but then the later is checking if we
have consumed the event so we have to. Maybe the introduction of the
drm_atomic_helper_fake_vblank() is needed in komeda as well like the generic
commit_tail helper function does? I need to investigate more the next time I get some
spare cycles on komeda.
I will send a new email with the updated patch and your Tested-by if that's OK.
All happy and fine with that.
Best regards,
Liviu
--8<---------------------------------------------------------------------------
From 76f9e5fed216a815e9eb56152f85454521079f10 Mon Sep 17 00:00:00 2001
From: Liviu Dudau <liviu.dudau@xxxxxxx>
Date: Fri, 8 Jul 2022 16:39:21 +0100
Subject: [PATCH] drm/komeda: Fix handling of atomic commits in the
atomic_commit_tail hook
Komeda driver relies on the generic DRM atomic helper functions to handle
commits. It only implements an atomic_commit_tail hook for the
mode_config_helper_funcs and even that one is pretty close to the generic
implementation with the exception of additional dma_fence signalling.
What the generic helper framework doesn't do is waiting for the actual
hardware to signal that the commit parameters have been written into the
appropriate registers. As we signal CRTC events only on the irq handlers,
we need to flush the configuration and wait for the hardware to respond.
Add the Komeda specific implementation for atomic_commit_hw_done() that
flushes and waits for flip done before calling drm_atomic_helper_commit_hw_done().
The fix was prompted by a patch from Carsten Haitzler where he was trying to
solve the same issue but in a different way that I think can lead to wrong
event signaling to userspace.
Reported-by: Carsten Haitzler <carsten.haitzler@xxxxxxx>
Signed-off-by: Liviu Dudau <liviu.dudau@xxxxxxx>
---
.../gpu/drm/arm/display/komeda/komeda_crtc.c | 4 ++--
.../gpu/drm/arm/display/komeda/komeda_kms.c | 20 ++++++++++++++++++-
.../gpu/drm/arm/display/komeda/komeda_kms.h | 2 ++
3 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
index 59172acb973803d..292f533d8cf0de6 100644
--- a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
+++ b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
@@ -235,7 +235,7 @@ void komeda_crtc_handle_event(struct komeda_crtc *kcrtc,
crtc->state->event = NULL;
drm_crtc_send_vblank_event(crtc, event);
} else {
- DRM_WARN("CRTC[%d]: FLIP happen but no pending commit.\n",
+ DRM_WARN("CRTC[%d]: FLIP happened but no pending commit.\n",
drm_crtc_index(&kcrtc->base));
}
spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
@@ -286,7 +286,7 @@ komeda_crtc_atomic_enable(struct drm_crtc *crtc,
komeda_crtc_do_flush(crtc, old);
}
-static void
+void
komeda_crtc_flush_and_wait_for_flip_done(struct komeda_crtc *kcrtc,
struct completion *input_flip_done)
{
diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
index 93b7f09b96ca950..1a53bd87e81d8ad 100644
--- a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
+++ b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
@@ -69,6 +69,24 @@ static const struct drm_driver komeda_kms_driver = {
.minor = 1,
};
+static void komeda_kms_atomic_commit_hw_done(struct drm_atomic_state *state)
+{
+ struct drm_device *dev = state->dev;
+ struct komeda_kms_dev *kms = to_kdev(dev);
+
+ for (int i = 0; i < kms->n_crtcs; i++) {
+ struct komeda_crtc *kcrtc = &kms->crtcs[i];
+
+ if (kcrtc->base.state->active) {
+ struct completion *flip_done = NULL;
+ if (kcrtc->base.state->event)
+ flip_done = kcrtc->base.state->event->base.completion;
+ komeda_crtc_flush_and_wait_for_flip_done(kcrtc, flip_done);
+ }
+ }
+ drm_atomic_helper_commit_hw_done(state);
+}
+
static void komeda_kms_commit_tail(struct drm_atomic_state *old_state)
{
struct drm_device *dev = old_state->dev;
@@ -81,7 +99,7 @@ static void komeda_kms_commit_tail(struct drm_atomic_state *old_state)
drm_atomic_helper_commit_modeset_enables(dev, old_state);
- drm_atomic_helper_commit_hw_done(old_state);
+ komeda_kms_atomic_commit_hw_done(old_state);
drm_atomic_helper_wait_for_flip_done(dev, old_state);
diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_kms.h b/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
index 456f3c435719317..bf6e8fba5061335 100644
--- a/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
+++ b/drivers/gpu/drm/arm/display/komeda/komeda_kms.h
@@ -182,6 +182,8 @@ void komeda_kms_cleanup_private_objs(struct komeda_kms_dev *kms);
void komeda_crtc_handle_event(struct komeda_crtc *kcrtc,
struct komeda_events *evts);
+void komeda_crtc_flush_and_wait_for_flip_done(struct komeda_crtc *kcrtc,
+ struct completion *input_flip_done);
struct komeda_kms_dev *komeda_kms_attach(struct komeda_dev *mdev);
void komeda_kms_detach(struct komeda_kms_dev *kms);
