On Thu, Jan 23, 2020 at 10:21:23AM +0100, Thomas Zimmermann wrote:
> The atomic helpers automatically send out fake VBLANK events if no
> vblanking has been initialized. This would apply to xen, but xen has
> its own vblank logic. To avoid interfering with the atomic helpers,
> disable automatic vblank events explictly.
>
> v4:
> * separate commit from core vblank changes
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Acked-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
On all the driver patches:
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
> drivers/gpu/drm/xen/xen_drm_front_kms.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/gpu/drm/xen/xen_drm_front_kms.c b/drivers/gpu/drm/xen/xen_drm_front_kms.c
> index 4f34c5208180..efde4561836f 100644
> --- a/drivers/gpu/drm/xen/xen_drm_front_kms.c
> +++ b/drivers/gpu/drm/xen/xen_drm_front_kms.c
> @@ -220,6 +220,18 @@ static bool display_send_page_flip(struct drm_simple_display_pipe *pipe,
> return false;
> }
>
> +static int display_check(struct drm_simple_display_pipe *pipe,
> + struct drm_plane_state *plane_state,
> + struct drm_crtc_state *crtc_state)
> +{
> + /* Make sure that DRM helpers don't send VBLANK events
> + * automatically. Xen has it's own logic to do so.
> + */
> + crtc_state->no_vblank = false;
So this here is strictly speaking dead code, because the fake_vblank
helper makes sure to only send out the event if it hasn't been processed
yet.
Which is a bit awkward, since it does this silently, potentially hiding
bugs. We already have a warning that complains if a crtc_state->event
hasn't been processed at all. But with the auto-vblank stuff here we kinda
defeat that a bit ... I think adding a WARN_ON in fake_vblank that fires
if no_vblank is set, but the event is somehow gone, would be really
useful. That would point at some serious driver snafu ...
Care to throw that on top?
-Daniel
> +
> + return 0;
> +}
> +
> static void display_update(struct drm_simple_display_pipe *pipe,
> struct drm_plane_state *old_plane_state)
> {
> @@ -284,6 +296,7 @@ static const struct drm_simple_display_pipe_funcs display_funcs = {
> .enable = display_enable,
> .disable = display_disable,
> .prepare_fb = drm_gem_fb_simple_display_pipe_prepare_fb,
> + .check = display_check,
> .update = display_update,
> };
>
> --
> 2.24.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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