Il 19/09/23 09:37, Jason-JH Lin (林睿祥) ha scritto:
Hi Angelo
Thanks for the reviews.
Hi Fei,
Thanks for the testing.
On Mon, 2023-09-18 at 18:47 +0800, Fei Shao wrote:
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Hi Angelo,
On Wed, Sep 13, 2023 at 4:35 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@xxxxxxxxxxxxx> wrote:
Il 22/08/23 15:26, Jason-JH.Lin ha scritto:
Add spinlock protection to avoid race condition on vblank event
between mtk_drm_crtc_atomic_begin() and
mtk_drm_finish_page_flip().
Hello Jason,
Can you please provide more information about this race condition?
(check below)
Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek
SoC MT8173.")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@xxxxxxxxxxxx>
---
drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
index d40142842f85..128a672fe3c9 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
@@ -746,6 +746,9 @@ static void mtk_drm_crtc_atomic_begin(struct
drm_crtc *crtc,
crtc);
struct mtk_crtc_state *mtk_crtc_state =
to_mtk_crtc_state(crtc_state);
struct mtk_drm_crtc *mtk_crtc = to_mtk_crtc(crtc);
+ unsigned long flags;
+
+ spin_lock_irqsave(&crtc->dev->event_lock, flags);
if (mtk_crtc->event && mtk_crtc_state->base.event)
DRM_ERROR("new event while there is still a pending
event\n");
@@ -756,6 +759,8 @@ static void mtk_drm_crtc_atomic_begin(struct
drm_crtc *crtc,
...because my suspect is that what creates the race condition in
this function is
the unlocked *assignment* to mtk_crtc->event, not the rest.
If I'm right, you don't need to unconditionally spinlock at the
beginning of this
function hence ever-so-slightly improving performance compared to
this version.
Can you please try this one and check if this *also* solves the
issue?
if (mtk_crtc_state->base.event) {
mtk_crtc_state->base.event->pipe =
drm_crtc_index(crtc);
WARN_ON(drm_crtc_vblank_get(crtc) != 0);
spin_lock_irqsave(&crtc->dev->event_lock, flags);
mtk_crtc->event = mtk_crtc_state->base.event;
spin_lock_irqrestore(&crtc->dev->event_lock,
flags);
mtk_crtc_state->base.event = NULL;
}
P.S.: I'd try that myself, but I can't seem to reproduce the issue.
I can't reproduce the system hang issue reported from customer by
toggling the night light mode in UI panel either.
But I can see the error message "new event while there is still a
pending event" when I was reproducing the issue.
Here is the debug info from "Wei-Shun <weishunc@xxxxxxxxxx>":
From the kernel tracing:
99342.377173: mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
99342.377226:
drm_crtc_send_vblank_event <-mtk_crtc_ddp_irq
99342.393831:
mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
99342.393887:
drm_crtc_send_vblank_event <-mtk_crtc_ddp_irq
99342.410469:
mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
99342.410519:
drm_crtc_send_vblank_event <-mtk_crtc_ddp_irq
99342.427094:
mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
99342.443831:
mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
99342.460495:
mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
99342.477157:
mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
99342.493841:
mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
99342.510453:
mtk_crtc_ddp_irq <-mtk_disp_ovl_irq_handler
Every mtk_crtc_ddp_irq should come with a drm_crtc_send_vblank_event.
However, when the issue happens, the mtk_crtc_ddp_irq keeps firing but
no drm_crtc_send_vblank_event. I suspect this is the main reason
causing flip_done timeout.
In mtk_drm_crtc.c, mtk_crtc->config_updating and mtk_crtc-
pending_needs_vblank are the conditions that may impact the vblank
event.
static void mtk_drm_finish_page_flip(struct mtk_drm_crtc *mtk_crtc)
{
struct drm_crtc *crtc = &mtk_crtc->base;
unsigned long flags;
drm_crtc_handle_vblank(&mtk_crtc->base);
spin_lock_irqsave(&crtc->dev->event_lock, flags);
==> if (!mtk_crtc->config_updating && mtk_crtc->pending_needs_vblank) {
mtk_drm_crtc_finish_page_flip(mtk_crtc);
mtk_crtc->pending_needs_vblank = false;
}
spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
}
There are 3 lines are called in mtk_drm_crtc_finish_page_flip():
drm_crtc_send_vblank_event(crtc, mtk_crtc->event);
drm_crtc_vblank_put(crtc);
mtk_crtc->event = NULL;
So I want to protect these 3 things to avoid them encountering race
conditions:
mtk_crtc_state->base.event //will be provided on atomic_commit complete
drm_crtc_vblank_get(crtc)
mtk_crtc->event
I have tried to protect this line only:
spin_lock_irqsave(&crtc->dev->event_lock, flags);
mtk_crtc->event = mtk_crtc_state->base.event;
spin_lock_irqrestore(&crtc->dev->event_lock,flags);
I can still see the error message "new event while there is still a
pending event" when I toggled the night light mode.
Maybe that is mtk_crtc->event here:
if (mtk_crtc->event && mtk_crtc_state->base.event)
haven't set to NULL by mtk_drm_crtc_finish_page_flip().
But that not a problem because we will protect mtk_crtc->event here:
mtk_crtc->event = mtk_crtc_state->base.event;
So should we remove that error message since it doesn't help and may
cause the confuse after we fix this issue?
I'm still able to reproduce it so I gave it a try, and this approach
also seems to fix the issue. :)
FWIW, the way I reproduce that is to toggle the night light mode on
and off repeatedly through the UI panel while playing YouTube videos
on my device.
Jason, can you post a new version with Angelo's suggestion?
OK, I can take Angelo's suggestion. Thanks!
But I am wondering if we should remove this log?
DRM_ERROR("new event while there is still a pending event\n");
Thanks for the analysis.
Please don't remove that line, this indicates that there might be another issue
somewhere else, and someone will tackle that later.
Regards,
Angelo
Regards,
Jason-JH.Lin
Regards,
Fei
Regards,
Angelo
