[PATCH] drm/amd/display: Fix flip-done timeouts on mode1 reset

From: Leo Li <[email protected]>

The vblank on/off callbacks mixed use of amdgpu_irq_get/put() and
amdgpu_dm_crtc_set_vupdate_irq() to enable and disable IRQs.

With get/put, base driver will callback into DC to disable IRQs when
refcount == 0. With set_vupdate_irq(), DC is called directly to disable
IRQs, bypassing base driver's refcount tracking.

During gpu reset, base driver can restore IRQs via
amdgpu_irq_gpu_reset_resume_helper() > amdgpu_irq_update(). So if
get/put() is not used (i.e. refcount == 0), then vupdate_irq will be
disabled.

This is problematic if DRM requests vblank on before amdgpu_irq_update()
is called: drm_vblank_on() > set_vupdate_irq() enables vupdate_irq, but
the refcount is still 0. gpu_reset_resume_helper() > irq_update() then
immediately disables it, thus leading to flip done timeouts.

This is made worse on DCN since VUPDATE_NO_LOCK is the only IRQ enabled.
Prior to 8382cd234981, a combination of GRPH_FLIP and VSTARTUP IRQs were
used, and they used get/put(). This explains why 8382cd234981 exposed
this issue.

Fix by using get/put() instead of set_vupdate_irq(). DCE is unchanged,
since it relies on unbalanced enable/disable calls based on VRR status,
and hence requires direct set_vupdate_irq(). Plus, it also uses
GRPH_FLIP and VLINE IRQs, which are properly tracked by get/put().

Cc: [email protected]
Fixes: 8382cd234981 ("drm/amd/display: consolidate DCN vblank/flip handling onto vupdate_no_lock")
Signed-off-by: Leo Li <[email protected]>
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c  | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
index 05d6915f9a6b0..079d4ccc88da6 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
@@ -287,10 +287,19 @@ static inline int amdgpu_dm_crtc_set_vblank(struct drm_crtc *crtc, bool enable)
 	 * is enabled. On DCE, vupdate is only needed in VRR mode.
 	 */
 	if (amdgpu_ip_version(adev, DCE_HWIP, 0) != 0) {
-		rc = amdgpu_dm_crtc_set_vupdate_irq(crtc, enable);
+		if (enable) {
+			rc = amdgpu_irq_get(adev, &adev->vupdate_irq, irq_type);
+			drm_dbg_vbl(crtc->dev, "Get vupdate_irq ret=%d\n", rc);
+		} else {
+			rc = amdgpu_irq_put(adev, &adev->vupdate_irq, irq_type);
+			drm_dbg_vbl(crtc->dev, "Put vupdate_irq ret=%d\n", rc);
+		}
 	} else if (dc_supports_vrr(dm->dc->ctx->dce_version)) {
 		if (enable) {
-			/* vblank irq on -> Only need vupdate irq in vrr mode */
+			/* vblank irq on -> Only need vupdate irq in vrr mode
+			 * Not ref-counted since we need explicit enable/disable
+			 * for DCE VRR handling
+			 */
 			if (amdgpu_dm_crtc_vrr_active(acrtc_state))
 				rc = amdgpu_dm_crtc_set_vupdate_irq(crtc, true);
 		} else {
-- 
2.54.0