From: Nicholas Kazlauskas nicholas.kazlauskas@amd.com
[ Upstream commit 520f08df45fbe300ed650da786a74093d658b7e1 ]
When variable refresh rate is active the hardware counter can return a position >= vtotal. This results in a vpos being returned from amdgpu_display_get_crtc_scanoutpos that's a positive value. The positive value indicates to the caller that the display is currently in scanout when the display is actually still in vblank.
This is because the vfront porch duration is unknown with variable refresh active and will end when either a page flip occurs or the timeout specified by the driver/display is reached.
The behavior of the amdgpu_display_get_crtc_scanoutpos remains the same when the position is below vtotal. When the position is above vtotal the function will return a value that is effectively -vbl_end, the size of the vback porch.
The only caller affected by this change is the DRM helper for calculating vblank timestamps. This change corrects behavior for calculating the page flip timestamp from being the previous timestamp to the calculation to the next timestamp when position >= vtotal.
Signed-off-by: Nicholas Kazlauskas nicholas.kazlauskas@amd.com Reviewed-by: Harry Wentland harry.wentland@amd.com Signed-off-by: Alex Deucher alexander.deucher@amd.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c index 15a2d8f3725d..5042ae072386 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c @@ -856,7 +856,12 @@ int amdgpu_get_crtc_scanoutpos(struct drm_device *dev, unsigned int pipe, /* Inside "upper part" of vblank area? Apply corrective offset if so: */ if (in_vbl && (*vpos >= vbl_start)) { vtotal = mode->crtc_vtotal; - *vpos = *vpos - vtotal; + + /* With variable refresh rate displays the vpos can exceed + * the vtotal value. Clamp to 0 to return -vbl_end instead + * of guessing the remaining number of lines until scanout. + */ + *vpos = (*vpos < vtotal) ? (*vpos - vtotal) : 0; }
/* Correct for shifted end of vbl at vbl_end. */