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drm/rockchip: explain why we can't wait_for_vblanks

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Signed-off-by: John Keeping <john@metanate.com>
This commit is contained in:
John Keeping 2016-01-19 10:47:00 +00:00 committed by Mark Yao
parent f2227f4697
commit c9ad1d9946
1 changed files with 15 additions and 0 deletions
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15
drivers/gpu/drm/rockchip/rockchip_drm_fb.c
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@ -176,6 +176,21 @@ static void rockchip_crtc_wait_for_update(struct drm_crtc *crtc)
crtc_funcs->wait_for_update(crtc);
}
/*
* We can't use drm_atomic_helper_wait_for_vblanks() because rk3288 and rk3066
* have hardware counters for neither vblanks nor scanlines, which results in
* a race where:
* | <-- HW vsync irq and reg take effect
* plane_commit --> |
* get_vblank and wait --> |
* | <-- handle_vblank, vblank->count + 1
* cleanup_fb --> |
* iommu crash --> |
* | <-- HW vsync irq and reg take effect
*
* This function is equivalent but uses rockchip_crtc_wait_for_update() instead
* of waiting for vblank_count to change.
*/
static void
rockchip_atomic_wait_for_complete(struct drm_device *dev, struct drm_atomic_state *old_state)
{