[Bug 1882851] [PATCH] drm/virtio: fix unblank

[Gerd Hoffmann]

When going through a disable/enable cycle without changing the framebuffer
the optimization added by commit 3954ff10e06e causes the screen stay
blank.  Add a bool to force an update to fix that.

Cc: 1882851@bugs.launchpad.net
Fixes: 3954ff10e06e ("drm/virtio: skip set_scanout if framebuffer didn't 
change")
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 drivers/gpu/drm/virtio/virtgpu_drv.h     | 1 +
 drivers/gpu/drm/virtio/virtgpu_display.c | 1 +
 drivers/gpu/drm/virtio/virtgpu_plane.c   | 4 +++-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h 
b/drivers/gpu/drm/virtio/virtgpu_drv.h
index 7879ff58236f..6d5410d5dd84 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.h
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
@@ -138,6 +138,7 @@ struct virtio_gpu_output {
        int cur_x;
        int cur_y;
        bool enabled;
+       bool need_update;
 };
 #define drm_crtc_to_virtio_gpu_output(x) \
        container_of(x, struct virtio_gpu_output, crtc)
diff --git a/drivers/gpu/drm/virtio/virtgpu_display.c 
b/drivers/gpu/drm/virtio/virtgpu_display.c
index 2b7e6ae65546..44e9c7b874f5 100644
--- a/drivers/gpu/drm/virtio/virtgpu_display.c
+++ b/drivers/gpu/drm/virtio/virtgpu_display.c
@@ -99,6 +99,7 @@ static void virtio_gpu_crtc_atomic_enable(struct drm_crtc 
*crtc,
        struct virtio_gpu_output *output = drm_crtc_to_virtio_gpu_output(crtc);
 
        output->enabled = true;
+       output->need_update = true;
 }
 
 static void virtio_gpu_crtc_atomic_disable(struct drm_crtc *crtc,
diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c 
b/drivers/gpu/drm/virtio/virtgpu_plane.c
index 52d24179bcec..5948031a9ce8 100644
--- a/drivers/gpu/drm/virtio/virtgpu_plane.c
+++ b/drivers/gpu/drm/virtio/virtgpu_plane.c
@@ -163,7 +163,8 @@ static void virtio_gpu_primary_plane_update(struct 
drm_plane *plane,
            plane->state->src_w != old_state->src_w ||
            plane->state->src_h != old_state->src_h ||
            plane->state->src_x != old_state->src_x ||
-           plane->state->src_y != old_state->src_y) {
+           plane->state->src_y != old_state->src_y ||
+           output->need_update) {
                DRM_DEBUG("handle 0x%x, crtc %dx%d+%d+%d, src %dx%d+%d+%d\n",
                          bo->hw_res_handle,
                          plane->state->crtc_w, plane->state->crtc_h,
@@ -178,6 +179,7 @@ static void virtio_gpu_primary_plane_update(struct 
drm_plane *plane,
                                           plane->state->src_h >> 16,
                                           plane->state->src_x >> 16,
                                           plane->state->src_y >> 16);
+               output->need_update = false;
        }
 
        virtio_gpu_cmd_resource_flush(vgdev, bo->hw_res_handle,
-- 
2.18.4

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https://bugs.launchpad.net/bugs/1882851

Title:
  QEMU video freezes with "Guest disabled display" (virtio driver)

Status in QEMU:
  New

Bug description:
  I am using Arch Linux as my Guest and Host OS, after starting qemu
  with the following command:

    $ qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga
  virtio

  and waiting for a screen blank, I get this message:

    Guest disabled display

  And nothing happens after that, I can move the mouse or hit any key,
  and the message is still there.

  I can still reboot the VM but that's not optimal.

  I can reproduce this with the latest QEMU release (5.0.0) or git master, 
  I also tried this with older releases (4.0.0, 3.0.0) and the issue is still 
there.

  I can't reproduce this with other video drivers (std, qxl).

  With std/qxl the screen will blank a bit and then continue as normal.

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