Re: [Xen-devel] [PATCH v5 15/15] drm/xen: Explicitly disable automatic sending of vblank event

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 1/29/20 2:05 PM, 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 explicitly.
>
> v5:
>       * update comment
> v4:
>       * separate commit from core vblank changes
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Acked-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Thank you for your work,
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> ---
>   drivers/gpu/drm/xen/xen_drm_front_kms.c | 19 +++++++++++++++++++
>   1 file changed, 19 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..78096bbcd226 100644
> --- a/drivers/gpu/drm/xen/xen_drm_front_kms.c
> +++ b/drivers/gpu/drm/xen/xen_drm_front_kms.c
> @@ -220,6 +220,24 @@ 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)
> +{
> +     /*
> +      * Xen doesn't initialize vblanking via drm_vblank_init(), so
> +      * DRM helpers assume that it doesn't handle vblanking and start
> +      * sending out fake VBLANK events automatically.
> +      *
> +      * As xen contains it's own logic for sending out VBLANK events
> +      * in send_pending_event(), disable no_vblank (i.e., the xen
> +      * driver has vblanking support).
> +      */
> +     crtc_state->no_vblank = false;
> +
> +     return 0;
> +}
> +
>   static void display_update(struct drm_simple_display_pipe *pipe,
>                          struct drm_plane_state *old_plane_state)
>   {
> @@ -284,6 +302,7 @@ 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,
>   };
>   
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