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authorDaniel Vetter <daniel.vetter@ffwll.ch>2021-02-09 11:15:23 +0100
committerDaniel Vetter <daniel.vetter@ffwll.ch>2021-02-10 12:38:55 +0100
commitf66aaab828e726986d9d5daa2b637b2712464a15 (patch)
treee6ae581e30780c387b21a44bf8189f8cd51c4781 /drivers/gpu/drm
parentc0f6f0c471a378a6da5ac99a086ba63e1a8570bb (diff)
drm/vblank: Document drm_crtc_vblank_restore constraints
I got real badly confused when trying to review a fix from Ville for this. Let's try to document better what's required for this, and check the minimal settings at runtime - we can't check ofc that there's indeed no races in the driver callback. Also noticed that the drm_vblank_restore version is unused, so lets unexport that while at it. Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Ville Syrjala <ville.syrjala@linux.intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20210209101523.2954281-1-daniel.vetter@ffwll.ch
Diffstat (limited to 'drivers/gpu/drm')
-rw-r--r--drivers/gpu/drm/drm_vblank.c25
1 files changed, 10 insertions, 15 deletions
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 893165eeddf3..2bd989688eae 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1470,20 +1470,7 @@ void drm_crtc_vblank_on(struct drm_crtc *crtc)
}
EXPORT_SYMBOL(drm_crtc_vblank_on);
-/**
- * drm_vblank_restore - estimate missed vblanks and update vblank count.
- * @dev: DRM device
- * @pipe: CRTC index
- *
- * Power manamement features can cause frame counter resets between vblank
- * disable and enable. Drivers can use this function in their
- * &drm_crtc_funcs.enable_vblank implementation to estimate missed vblanks since
- * the last &drm_crtc_funcs.disable_vblank using timestamps and update the
- * vblank counter.
- *
- * This function is the legacy version of drm_crtc_vblank_restore().
- */
-void drm_vblank_restore(struct drm_device *dev, unsigned int pipe)
+static void drm_vblank_restore(struct drm_device *dev, unsigned int pipe)
{
ktime_t t_vblank;
struct drm_vblank_crtc *vblank;
@@ -1519,7 +1506,6 @@ void drm_vblank_restore(struct drm_device *dev, unsigned int pipe)
diff, diff_ns, framedur_ns, cur_vblank - vblank->last);
store_vblank(dev, pipe, diff, t_vblank, cur_vblank);
}
-EXPORT_SYMBOL(drm_vblank_restore);
/**
* drm_crtc_vblank_restore - estimate missed vblanks and update vblank count.
@@ -1530,9 +1516,18 @@ EXPORT_SYMBOL(drm_vblank_restore);
* &drm_crtc_funcs.enable_vblank implementation to estimate missed vblanks since
* the last &drm_crtc_funcs.disable_vblank using timestamps and update the
* vblank counter.
+ *
+ * Note that drivers must have race-free high-precision timestamping support,
+ * i.e. &drm_crtc_funcs.get_vblank_timestamp must be hooked up and
+ * &drm_driver.vblank_disable_immediate must be set to indicate the
+ * time-stamping functions are race-free against vblank hardware counter
+ * increments.
*/
void drm_crtc_vblank_restore(struct drm_crtc *crtc)
{
+ WARN_ON_ONCE(!crtc->funcs->get_vblank_timestamp);
+ WARN_ON_ONCE(!crtc->dev->vblank_disable_immediate);
+
drm_vblank_restore(crtc->dev, drm_crtc_index(crtc));
}
EXPORT_SYMBOL(drm_crtc_vblank_restore);