[PATCH 5/6] drm/hypervdrm: Use vblank timer

[Thomas Zimmermann]

HyperV's virtual hardware does not provide vblank interrupts. Use a
vblank timer to simulate the interrupt in software. Rate-limits the
display's update frequency to the display-mode settings. Avoids
excessive CPU overhead with compositors that do not rate-limit their
output.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
---
 drivers/gpu/drm/hyperv/hyperv_drm.h         |  4 ++
 drivers/gpu/drm/hyperv/hyperv_drm_modeset.c | 70 +++++++++++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/drivers/gpu/drm/hyperv/hyperv_drm.h b/drivers/gpu/drm/hyperv/hyperv_drm.h
index 9e776112c03e..730e4a37545d 100644
--- a/drivers/gpu/drm/hyperv/hyperv_drm.h
+++ b/drivers/gpu/drm/hyperv/hyperv_drm.h
@@ -6,12 +6,16 @@
 #ifndef _HYPERV_DRM_H_
 #define _HYPERV_DRM_H_
 
+#include <drm/drm_vblank.h>
+#include <drm/drm_vblank_timer.h>
+
 #define VMBUS_MAX_PACKET_SIZE 0x4000
 
 struct hyperv_drm_device {
 	/* drm */
 	struct drm_device dev;
 	struct drm_plane plane;
+	struct drm_vblank_timer vtimer;
 	struct drm_crtc crtc;
 	struct drm_encoder encoder;
 	struct drm_connector connector;
diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c b/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
index f7d2e973f79e..ed19e471b96f 100644
--- a/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
@@ -97,6 +97,28 @@ static const uint64_t hyperv_modifiers[] = {
 	DRM_FORMAT_MOD_INVALID
 };
 
+static void hyperv_crtc_helper_atomic_flush(struct drm_crtc *crtc,
+					    struct drm_atomic_state *state)
+{
+	struct drm_device *dev = crtc->dev;
+	struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
+	struct drm_pending_vblank_event *event;
+
+	spin_lock_irq(&dev->event_lock);
+
+	event = crtc_state->event;
+	crtc_state->event = NULL;
+
+	if (event) {
+		if (drm_crtc_vblank_get(crtc) == 0)
+			drm_crtc_arm_vblank_event(crtc, event);
+		else
+			drm_crtc_send_vblank_event(crtc, event);
+	}
+
+	spin_unlock_irq(&dev->event_lock);
+}
+
 static void hyperv_crtc_helper_atomic_enable(struct drm_crtc *crtc,
 					     struct drm_atomic_state *state)
 {
@@ -110,13 +132,49 @@ static void hyperv_crtc_helper_atomic_enable(struct drm_crtc *crtc,
 				crtc_state->mode.hdisplay,
 				crtc_state->mode.vdisplay,
 				plane_state->fb->pitches[0]);
+
+	drm_crtc_vblank_on(crtc);
+}
+
+static void hyperv_crtc_helper_atomic_disable(struct drm_crtc *crtc,
+					      struct drm_atomic_state *crtc_state)
+{
+	drm_crtc_vblank_off(crtc);
 }
 
 static const struct drm_crtc_helper_funcs hyperv_crtc_helper_funcs = {
 	.atomic_check = drm_crtc_helper_atomic_check,
+	.atomic_flush = hyperv_crtc_helper_atomic_flush,
 	.atomic_enable = hyperv_crtc_helper_atomic_enable,
+	.atomic_disable = hyperv_crtc_helper_atomic_disable,
 };
 
+static int hyperv_crtc_enable_vblank(struct drm_crtc *crtc)
+{
+	struct hyperv_drm_device *hv = to_hv(crtc->dev);
+
+	drm_vblank_timer_start(&hv->vtimer);
+
+	return 0;
+}
+
+static void hyperv_crtc_disable_vblank(struct drm_crtc *crtc)
+{
+	struct hyperv_drm_device *hv = to_hv(crtc->dev);
+
+	drm_vblank_timer_cancel(&hv->vtimer);
+}
+
+static bool hyperv_crtc_get_vblank_timestamp(struct drm_crtc *crtc,
+					     int *max_error, ktime_t *vblank_time,
+					     bool in_vblank_irq)
+{
+	struct hyperv_drm_device *hv = to_hv(crtc->dev);
+
+	return drm_vblank_timer_get_vblank_timestamp(&hv->vtimer, max_error,
+						     vblank_time, in_vblank_irq);
+}
+
 static const struct drm_crtc_funcs hyperv_crtc_funcs = {
 	.reset = drm_atomic_helper_crtc_reset,
 	.destroy = drm_crtc_cleanup,
@@ -124,6 +182,9 @@ static const struct drm_crtc_funcs hyperv_crtc_funcs = {
 	.page_flip = drm_atomic_helper_page_flip,
 	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
+	.enable_vblank = hyperv_crtc_enable_vblank,
+	.disable_vblank = hyperv_crtc_disable_vblank,
+	.get_vblank_timestamp = hyperv_crtc_get_vblank_timestamp,
 };
 
 static int hyperv_plane_atomic_check(struct drm_plane *plane,
@@ -285,6 +346,15 @@ int hyperv_mode_config_init(struct hyperv_drm_device *hv)
 		return ret;
 	}
 
+	/* Vertical blanking */
+
+	ret = drm_vblank_init(dev, 1);
+	if (ret)
+		return ret;
+	ret = drmm_vblank_timer_init(&hv->vtimer, &hv->crtc, NULL);
+	if (ret)
+		return ret;
+
 	drm_mode_config_reset(dev);
 
 	return 0;
-- 
2.49.0