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@xxxxxxxxxxx>
> ---
> 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. 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.
--
Earthling Michel Dänzer | http://www.amd.com
Libre software enthusiast | Mesa and X developer
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