From f66aaab828e726986d9d5daa2b637b2712464a15 Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Tue, 9 Feb 2021 11:15:23 +0100 Subject: drm/vblank: Document drm_crtc_vblank_restore constraints MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Cc: Ville Syrjala Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210209101523.2954281-1-daniel.vetter@ffwll.ch --- drivers/gpu/drm/drm_vblank.c | 25 ++++++++++--------------- 1 file changed, 10 insertions(+), 15 deletions(-) (limited to 'drivers/gpu/drm/drm_vblank.c') 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); -- cgit