Re: [PATCH v2 1/5] drm/rockchip: fix fb references in async update

[Helen Koike]

On 3/12/19 3:34 AM, Boris Brezillon wrote:
> On Mon, 11 Mar 2019 23:21:59 -0300
> Helen Koike <helen.koike@xxxxxxxxxxxxx> wrote:
> 
>> In the case of async update, modifications are done in place, i.e. in the
>> current plane state, so the new_state is prepared and the new_state is
>> cleanup up (instead of the old_state, diferrently on what happen in a
> 
>   ^ cleaned up				^ differently (but maybe
> "unlike what happens" is more appropriate here).
> 
>> normal sync update).
>> To cleanup the old_fb properly, it needs to be placed in the new_state
>> in the end of async_update, so cleanup call will unreference the old_fb
>> correctly.
>>
>> Also, the previous code had a:
>>
>> 	plane_state = plane->funcs->atomic_duplicate_state(plane);
>> 	...
>> 	swap(plane_state, plane->state);
>>
>> 	if (plane->state->fb && plane->state->fb != new_state->fb) {
>> 	...
>> 	}
>>
>> Which was wrong, as the fb were just assigned to be equal, so this if
>> statement nevers evaluates to true.
>>
>> Another details is that the function drm_crtc_vblank_get() can only be
>> called when vop->is_enabled is true, otherwise it has no effect and
>> trows a WARN_ON().
>>
>> Calling drm_atomic_set_fb_for_plane() (which get a referent of the new
>> fb and pus the old fb) is not required, as it is taken care by
>> drm_mode_cursor_universal() when calling
>> drm_atomic_helper_update_plane().
>>
>> Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
>>
>> ---
>> Hello,
>>
>> I tested on the rockchip ficus v1.1 using igt plane_cursor_legacy and
>> kms_cursor_legacy and I didn't see any regressions.
>>
>> Changes in v2: None
>>
>>  drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 42 ++++++++++++---------
>>  1 file changed, 24 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>> index c7d4c6073ea5..a1ee8c156a7b 100644
>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>> @@ -912,30 +912,31 @@ static void vop_plane_atomic_async_update(struct drm_plane *plane,
>>  					  struct drm_plane_state *new_state)
>>  {
>>  	struct vop *vop = to_vop(plane->state->crtc);
>> -	struct drm_plane_state *plane_state;
>> +	struct drm_framebuffer *old_fb = plane->state->fb;
>>  
>> -	plane_state = plane->funcs->atomic_duplicate_state(plane);
>> -	plane_state->crtc_x = new_state->crtc_x;
>> -	plane_state->crtc_y = new_state->crtc_y;
>> -	plane_state->crtc_h = new_state->crtc_h;
>> -	plane_state->crtc_w = new_state->crtc_w;
>> -	plane_state->src_x = new_state->src_x;
>> -	plane_state->src_y = new_state->src_y;
>> -	plane_state->src_h = new_state->src_h;
>> -	plane_state->src_w = new_state->src_w;
>> -
>> -	if (plane_state->fb != new_state->fb)
>> -		drm_atomic_set_fb_for_plane(plane_state, new_state->fb);
>> -
>> -	swap(plane_state, plane->state);
>> -
>> -	if (plane->state->fb && plane->state->fb != new_state->fb) {
>> +	/*
>> +	 * A scanout can still be occurring, so we can't drop the reference to
>> +	 * the old framebuffer. To solve this we get a reference to old_fb and
>> +	 * set a worker to release it later.
> 
> Hm, doesn't look like an async update to me if we have to wait for the
> next VBLANK to happen to get the new content on the screen. Maybe we
> should reject async updates when old_fb != new_fb in the rk
> ->async_check() hook.

Unless I am misunderstanding this, we don't wait here, we just grab a
reference to the fb in case it is being still used by the hw, so it
doesn't get released prematurely.

> 
>> +	 */
>> +	if (vop->is_enabled &&
>> +	    plane->state->fb && plane->state->fb != new_state->fb) {
>>  		drm_framebuffer_get(plane->state->fb);
>>  		WARN_ON(drm_crtc_vblank_get(plane->state->crtc) != 0);
>>  		drm_flip_work_queue(&vop->fb_unref_work, plane->state->fb);
>>  		set_bit(VOP_PENDING_FB_UNREF, &vop->pending);
>>  	}
> 
> In any case, I think this should be called after
> vop_plane_atomic_update() to prevent the situation where the VBLANK
> event happens between this point and the following
> vop_plane_atomic_update() call.

ack, I'll update it in the next version.

> 
>>  
>> +	plane->state->crtc_x = new_state->crtc_x;
>> +	plane->state->crtc_y = new_state->crtc_y;
>> +	plane->state->crtc_h = new_state->crtc_h;
>> +	plane->state->crtc_w = new_state->crtc_w;
>> +	plane->state->src_x = new_state->src_x;
>> +	plane->state->src_y = new_state->src_y;
>> +	plane->state->src_h = new_state->src_h;
>> +	plane->state->src_w = new_state->src_w;
>> +	plane->state->fb = new_state->fb;
> 
> Any reason not to use swap() here and reference plane->state->fb
> instead of new_state->fb after this point?

I had the impression I had to do this in one of my tests, but re-testing
now and re-looking at the code this doesn't seem to be necessary. I'll
use a swap() in the next version.

Thanks for your feedback.
Helen

> 
>> +
>>  	if (vop->is_enabled) {
>>  		rockchip_drm_psr_inhibit_get_state(new_state->state);
>>  		vop_plane_atomic_update(plane, plane->state);
>> @@ -945,7 +946,12 @@ static void vop_plane_atomic_async_update(struct drm_plane *plane,
>>  		rockchip_drm_psr_inhibit_put_state(new_state->state);
>>  	}
>>  
>> -	plane->funcs->atomic_destroy_state(plane, plane_state);
>> +	/*
>> +	 * In async update we perform inplace modifications and release the
>> +	 * new_state. The following is required so we release the reference of
>> +	 * the old framebuffer.
>> +	 */
>> +	new_state->fb = old_fb;
>>  }
>>  
>>  static const struct drm_plane_helper_funcs plane_helper_funcs = {
>