From c71f09dafd82a37a488029f33552a45a99d0a9a6 Mon Sep 17 00:00:00 2001
From: Eric Anholt <eric@anholt.net>
Date: Tue, 2 Apr 2019 13:29:00 -0700
Subject: [PATCH] drm/vc4: Fix vblank timestamping for firmwarekms.

The core doesn't expect a false return from the scanoutpos function in
normal usage, so we were doing the precise vblank timestamping path
and thus "immediate" vblank disables (even though firmwarekms can't
actually disable vblanks interrupts, sigh), and the kernel would get
confused when getting timestamp info when also turning vblanks back
on.

Signed-off-by: Eric Anholt <eric@anholt.net>
---
 drivers/gpu/drm/vc4/vc4_crtc.c         | 3 ---
 drivers/gpu/drm/vc4/vc4_firmware_kms.c | 7 +++++++
 2 files changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -97,9 +97,6 @@ bool vc4_crtc_get_scanoutpos(struct drm_
 	int vblank_lines;
 	bool ret = false;
 
-	if (vc4->firmware_kms)
-		return 0;
-
 	/* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */
 
 	/* Get optional system timestamp before query. */
--- a/drivers/gpu/drm/vc4/vc4_firmware_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_firmware_kms.c
@@ -20,6 +20,7 @@
 #include "drm/drm_crtc_helper.h"
 #include "drm/drm_fourcc.h"
 #include "drm/drm_probe_helper.h"
+#include "drm/drm_drv.h"
 #include "linux/clk.h"
 #include "linux/debugfs.h"
 #include "drm/drm_fb_cma_helper.h"
@@ -673,6 +674,12 @@ static int vc4_fkms_bind(struct device *
 
 	vc4->firmware_kms = true;
 
+	/* firmware kms doesn't have precise a scanoutpos implementation, so
+	 * we can't do the precise vblank timestamp mode.
+	 */
+	drm->driver->get_scanout_position = NULL;
+	drm->driver->get_vblank_timestamp = NULL;
+
 	vc4_crtc = devm_kzalloc(dev, sizeof(*vc4_crtc), GFP_KERNEL);
 	if (!vc4_crtc)
 		return -ENOMEM;
