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drm/vblank: Document drm_crtc_vblank_restore constraints

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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
This commit is contained in:
Daniel Vetter 2021-02-09 11:15:23 +01:00
parent c0f6f0c471
commit f66aaab828
2 changed files with 10 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
drivers/gpu/drm/drm_vblank.c
View File

@ -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);

1
include/drm/drm_vblank.h
View File

@ -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,