On 09.03.2017 04:54, Michel Dänzer wrote:
On 08/03/17 11:58 PM, Andrzej Hajda wrote:
Current implementation of event handling assumes that vblank interrupt is always called at the right time. It is not true, it can be delayed due to various reasons. As a result different races can happen. The patch fixes the issue by using hardware frame counter present in DECON to serialize vblank and commit completion events.
Signed-off-by: Andrzej Hajda a.hajda@samsung.com
v2:
- added internal decon_get_frame_count function,
- updated frame counter on flush,
- misc style fixes (thank Inki)
[...]
@@ -579,6 +636,23 @@ static const struct component_ops decon_component_ops = { .unbind = decon_unbind, };
+static void decon_handle_vblank(struct decon_context *ctx) +{
- u32 frm;
- spin_lock(&ctx->vblank_lock);
- frm = decon_get_frame_count(ctx, true);
- if (frm != ctx->frame_id) {
if (frm > ctx->frame_id)drm_crtc_handle_vblank(&ctx->crtc->base);This comparison isn't safe WRT the counter value returned by decon_get_frame_count wrapping around.
And knowing that max framerate is 60fps it will happen after:
0xffffffff / 60fps / 60sec / 60min / 24h / 365days = 2.3 years
So after 2.3 years of uninterrupted work of panel/TV we will lose one or two vblanks :) Highly improbable and even then low damage.
If it goes all the way up to 0xffffffff before wrapping around to zero, it can be handled e.g. by
if ((s32)(frm - ctx->frame_id) > 0)otherwise it gets a bit more complicated.
But the fix looks simple so I think it is worth to fix it. Thanks.
Regards
Andrzej