Messages in this thread | | | From | Jason-JH Lin (林睿祥) <> | Subject | Re: [PATCH] drm/mediatek: Add spinlock for setting vblank event in atomic_begin | Date | Tue, 19 Sep 2023 07:37:28 +0000 |
| |
Hi Angelo
Thanks for the reviews.
Hi Fei,
Thanks for the testing.
On Mon, 2023-09-18 at 18:47 +0800, Fei Shao wrote: > > External email : Please do not click links or open attachments until > you have verified the sender or the content. > Hi Angelo, > > On Wed, Sep 13, 2023 at 4:35 PM AngeloGioacchino Del Regno > <angelogioacchino.delregno@collabora.com> 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@mediatek.com> > > > --- > > > 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@google.com>":
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");
Regards, Jason-JH.Lin
> Regards, > Fei > > > > > Regards, > > Angelo > > >
| |