Commit f66aaab8 authored by Daniel Vetter's avatar Daniel Vetter
Browse files

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: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210209101523.2954281-1-daniel.vetter@ffwll.ch
parent c0f6f0c4

drivers/gpu/drm/drm_vblank.c

+10 −15
Original line number Diff line number Diff line
@@ -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);

include/drm/drm_vblank.h

+0 −1
Original line number Diff line number Diff line
@@ -247,7 +247,6 @@ void drm_crtc_vblank_off(struct drm_crtc *crtc); 
void drm_crtc_vblank_reset(struct drm_crtc *crtc);

void drm_crtc_vblank_on(struct drm_crtc *crtc);

u64 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc);

void drm_vblank_restore(struct drm_device *dev, unsigned int pipe);

void drm_crtc_vblank_restore(struct drm_crtc *crtc);



void drm_calc_timestamping_constants(struct drm_crtc *crtc,