[PATCH 1/5] drm/vblank: Add drm_device.has_hw_vblank

[Lyude Paul]

Currently the way we check if a driver supports hardware vblanks or not is
actually funny and cursed! Likely because it predates KMS.

As it turns out, we only check dev->num_crtcs to see if we have vblank
support. Why? Because it doesn't actually represent the number of CRTCs on
the device, unless drm_vblank_init() has been called - which sets
dev->num_crtcs. And as it turns out, this is the second place we keep track
of the number of CRTCs we have.

Let's clean this up by starting with adding a variable specifically for
tracking whether drm_vblank_init() has been called or not.

Signed-off-by: Lyude Paul <lyude at redhat.com>
---
 drivers/gpu/drm/drm_vblank.c | 3 ++-
 include/drm/drm_device.h     | 7 +++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index f90fb2d13e423..d317148af8cb3 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -557,6 +557,7 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
 	if (!dev->vblank)
 		return -ENOMEM;
 
+	dev->has_hw_vblank = true;
 	dev->num_crtcs = num_crtcs;
 
 	for (i = 0; i < num_crtcs; i++) {
@@ -600,7 +601,7 @@ EXPORT_SYMBOL(drm_vblank_init);
  */
 bool drm_dev_has_vblank(const struct drm_device *dev)
 {
-	return dev->num_crtcs != 0;
+	return dev->has_hw_vblank;
 }
 EXPORT_SYMBOL(drm_dev_has_vblank);
 
diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index 768a8dae83c52..2df08c756afd3 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -287,6 +287,13 @@ struct drm_device {
 	 */
 	struct drm_vblank_crtc *vblank;
 
+	/**
+	 * @has_hw_vblank:
+	 *
+	 * Has the driver called drm_vblank_init() to setup hardware vblank support?
+	 */
+	bool has_hw_vblank;
+
 	/**
 	 * @vblank_time_lock:
 	 *
-- 
2.55.0