[PATCH V2] drm/vkms: Add support for vkms work without vblank

[Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>]

Currently, vkms needs VBlank to work well. This patch adds another
operation model that make vkms works without VBlank support. In this
scenario, vblank signaling is faked by calling drm_send_vblank_event()
in vkms_crtc_atomic_flush(); this approach works due to the
drm_vblank_get() == 0 verification.

Changes since V1:
  Daniel Vetter:
  - Change module parameter name from disablevblank to virtual_hw
  - Improve parameter description
  - Improve commit message

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>
---
 drivers/gpu/drm/vkms/vkms_crtc.c | 10 ++++++++++
 drivers/gpu/drm/vkms/vkms_drv.c  | 13 +++++++++++--
 drivers/gpu/drm/vkms/vkms_drv.h  |  1 +
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
index bfe6e0312cc4..001fa5c1d326 100644
--- a/drivers/gpu/drm/vkms/vkms_crtc.c
+++ b/drivers/gpu/drm/vkms/vkms_crtc.c
@@ -145,12 +145,22 @@ static const struct drm_crtc_funcs vkms_crtc_funcs = {
 static void vkms_crtc_atomic_enable(struct drm_crtc *crtc,
 				    struct drm_crtc_state *old_state)
 {
+	struct vkms_output *vkms_out = drm_crtc_to_vkms_output(crtc);
+
+	if (vkms_out->disable_vblank)
+		return;
+
 	drm_crtc_vblank_on(crtc);
 }
 
 static void vkms_crtc_atomic_disable(struct drm_crtc *crtc,
 				     struct drm_crtc_state *old_state)
 {
+	struct vkms_output *vkms_out = drm_crtc_to_vkms_output(crtc);
+
+	if (vkms_out->disable_vblank)
+		return;
+
 	drm_crtc_vblank_off(crtc);
 }
 
diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
index 5d78bd97e69c..0b6569ee9dcc 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.c
+++ b/drivers/gpu/drm/vkms/vkms_drv.c
@@ -21,6 +21,11 @@
 
 static struct vkms_device *vkms_device;
 
+static bool virtual_hw;
+module_param_named(virtual_hw, virtual_hw, bool, 0444);
+MODULE_PARM_DESC(virtual_hw,
+		 "Enable virtual hardware mode (disables vblanks and immediately completes flips)");
+
 static const struct file_operations vkms_driver_fops = {
 	.owner		= THIS_MODULE,
 	.open		= drm_open,
@@ -105,9 +110,13 @@ static int __init vkms_init(void)
 		goto out_fini;
 	}
 
-	vkms_device->drm.irq_enabled = true;
+	vkms_device->output.disable_vblank = virtual_hw;
+	vkms_device->drm.irq_enabled = !virtual_hw;
+
+	if (virtual_hw)
+		DRM_INFO("Virtual Hardware mode enabled");
 
-	ret = drm_vblank_init(&vkms_device->drm, 1);
+	ret = (virtual_hw) ? 0 : drm_vblank_init(&vkms_device->drm, 1);
 	if (ret) {
 		DRM_ERROR("Failed to vblank\n");
 		goto out_fini;
diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
index f156c930366a..9ee862e6f7e5 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.h
+++ b/drivers/gpu/drm/vkms/vkms_drv.h
@@ -52,6 +52,7 @@ struct vkms_output {
 	struct drm_encoder encoder;
 	struct drm_connector connector;
 	struct hrtimer vblank_hrtimer;
+	bool disable_vblank;
 	ktime_t period_ns;
 	struct drm_pending_vblank_event *event;
 	bool crc_enabled;
-- 
2.18.0
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