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[PATCH] drm/rockchip: Return -EBUSY if there's already a pending flip event v3

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  [PATCH] drm/rockchip: Return -EBUSY if there's already a pending flip event v3 Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2016-04-04 16:00 +0200
    Re: [PATCH] drm/rockchip: Return -EBUSY if there's already a pending  flip event v3 Daniel Stone <daniel@fooishbar.org> - 2016-04-04 17:50 +0200
      Re: [PATCH] drm/rockchip: Return -EBUSY if there's already a pending  flip event v3 Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2016-04-05 16:10 +0200

#1370632 — [PATCH] drm/rockchip: Return -EBUSY if there's already a pending flip event v3

As per the docs, atomic_commit should return -EBUSY "if an asycnhronous
updated is requested and there is an earlier updated pending".

v2: Use the status of the workqueue instead of vop->event, and don't add
a superfluous wait on the workqueue.

v3: Drop work_busy, as there's a sizeable delay when the worker
finishes, which introduces a race in which the client has already
received the last flip event but the next page flip ioctl will still
return -EBUSY because work_busy returns outdated information.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
---
 drivers/gpu/drm/rockchip/rockchip_drm_drv.h |  1 +
 drivers/gpu/drm/rockchip/rockchip_drm_fb.c  | 13 ++++++++++++-
 drivers/gpu/drm/rockchip/rockchip_drm_vop.c |  5 +++++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.h b/drivers/gpu/drm/rockchip/rockchip_drm_drv.h
index 3529f692edb8..37952eefd33d 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.h
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.h
@@ -69,6 +69,7 @@ int rockchip_register_crtc_funcs(struct drm_crtc *crtc,
 void rockchip_unregister_crtc_funcs(struct drm_crtc *crtc);
 int rockchip_drm_crtc_mode_config(struct drm_crtc *crtc, int connector_type,
 				  int out_mode);
+bool rockchip_drm_crtc_has_pending_event(struct drm_crtc *crtc);
 int rockchip_drm_dma_attach_device(struct drm_device *drm_dev,
 				   struct device *dev);
 void rockchip_drm_dma_detach_device(struct drm_device *drm_dev,
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
index 3b8f652698f8..8305bbd2a4d7 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
@@ -280,7 +280,18 @@ int rockchip_drm_atomic_commit(struct drm_device *dev,
 {
 	struct rockchip_drm_private *private = dev->dev_private;
 	struct rockchip_atomic_commit *commit = &private->commit;
-	int ret;
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc *crtc;
+	int i, ret;
+
+	if (async) {
+		for_each_crtc_in_state(state, crtc, crtc_state, i) {
+			if (crtc->state->event ||
+			    rockchip_drm_crtc_has_pending_event(crtc)) {
+				return -EBUSY;
+			}
+		}
+	}
 
 	ret = drm_atomic_helper_prepare_planes(dev, state);
 	if (ret)
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
index e2118e62345b..5bcdd8dc7499 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
@@ -848,6 +848,11 @@ int rockchip_drm_crtc_mode_config(struct drm_crtc *crtc,
 }
 EXPORT_SYMBOL_GPL(rockchip_drm_crtc_mode_config);
 
+bool rockchip_drm_crtc_has_pending_event(struct drm_crtc *crtc)
+{
+	return to_vop(crtc)->event;
+}
+
 static int vop_crtc_enable_vblank(struct drm_crtc *crtc)
 {
 	struct vop *vop = to_vop(crtc);
-- 
2.5.5

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#1370705 — Re: [PATCH] drm/rockchip: Return -EBUSY if there's already a pending flip event v3

Hi Tomeu,

On 4 April 2016 at 14:55, Tomeu Vizoso <tomeu.vizoso@collabora.com> wrote:
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> index 3b8f652698f8..8305bbd2a4d7 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> @@ -280,7 +280,18 @@ int rockchip_drm_atomic_commit(struct drm_device *dev,
>  {
>         struct rockchip_drm_private *private = dev->dev_private;
>         struct rockchip_atomic_commit *commit = &private->commit;
> -       int ret;
> +       struct drm_crtc_state *crtc_state;
> +       struct drm_crtc *crtc;
> +       int i, ret;
> +
> +       if (async) {
> +               for_each_crtc_in_state(state, crtc, crtc_state, i) {
> +                       if (crtc->state->event ||
> +                           rockchip_drm_crtc_has_pending_event(crtc)) {
> +                               return -EBUSY;
> +                       }
> +               }
> +       }

Hmmm ...

Doesn't this trigger before the VOP atomic_begin() helper, meaning
that anything with an event set will trigger the check? Seems like it
should be && rather than ||.

Also, I know rockchip_drm_vop.c isn't holding dev->event_lock when it
checks vop->event, but it really should be ... and so should this
check. Otherwise you can race with the IRQ handler, which isn't
required to hold the CRTC lock.

Cheers,
Daniel

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#1371640 — Re: [PATCH] drm/rockchip: Return -EBUSY if there's already a pending flip event v3

On 4 April 2016 at 17:44, Daniel Stone <daniel@fooishbar.org> wrote:
> Hi Tomeu,
>
> On 4 April 2016 at 14:55, Tomeu Vizoso <tomeu.vizoso@collabora.com> wrote:
>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>> index 3b8f652698f8..8305bbd2a4d7 100644
>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
>> @@ -280,7 +280,18 @@ int rockchip_drm_atomic_commit(struct drm_device *dev,
>>  {
>>         struct rockchip_drm_private *private = dev->dev_private;
>>         struct rockchip_atomic_commit *commit = &private->commit;
>> -       int ret;
>> +       struct drm_crtc_state *crtc_state;
>> +       struct drm_crtc *crtc;
>> +       int i, ret;
>> +
>> +       if (async) {
>> +               for_each_crtc_in_state(state, crtc, crtc_state, i) {
>> +                       if (crtc->state->event ||
>> +                           rockchip_drm_crtc_has_pending_event(crtc)) {
>> +                               return -EBUSY;
>> +                       }
>> +               }
>> +       }
>
> Hmmm ...
>
> Doesn't this trigger before the VOP atomic_begin() helper, meaning
> that anything with an event set will trigger the check? Seems like it
> should be && rather than ||.

So, these are the two cases that this code aims to handle:

1. A previous request with an event set hasn't progressed to
atomic_begin yet, so the event field in drm_crtc_state (at this point,
the old state) is still populated but vop->event still isn't.

2. A previous request has already progressed to atomic_begin but we
haven't gotten yet the interrupt that signals its completion, so
vop->event is populated but crtc->state->event isn't anymore.

My understanding is that in both cases there's a pending flip event
and we have to return -EBUSY if it's as async request.

> Also, I know rockchip_drm_vop.c isn't holding dev->event_lock when it
> checks vop->event, but it really should be ... and so should this
> check. Otherwise you can race with the IRQ handler, which isn't
> required to hold the CRTC lock.

Cool, thanks.

Tomeu

> Cheers,
> Daniel
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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