From: Robert Beckett <bob.beckett@collabora.com>
To: dri-devel@lists.freedesktop.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Maxime Ripard <maxime.ripard@bootlin.com>,
Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
Daniel Vetter <daniel@ffwll.ch>,
Philipp Zabel <p.zabel@pengutronix.de>,
Shawn Guo <shawnguo@kernel.org>,
Sascha Hauer <s.hauer@pengutronix.de>,
Pengutronix Kernel Team <kernel@pengutronix.de>,
Fabio Estevam <festevam@gmail.com>,
NXP Linux Team <linux-imx@nxp.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Robert Beckett <bob.beckett@collabora.com>
Subject: [PATCH v3 1/4] drm/vblank: warn on sending stale event
Date: Tue, 25 Jun 2019 18:59:12 +0100 [thread overview]
Message-ID: <a21034afa30246f31daa16e74a0772377a4791ef.1561483965.git.bob.beckett@collabora.com> (raw)
In-Reply-To: <cover.1561483965.git.bob.beckett@collabora.com>
Warn when about to send stale vblank info and add advice to
documentation on how to avoid.
Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
---
drivers/gpu/drm/drm_vblank.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 603ab105125d..7dabb2bdb733 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -918,6 +918,19 @@ EXPORT_SYMBOL(drm_crtc_arm_vblank_event);
*
* See drm_crtc_arm_vblank_event() for a helper which can be used in certain
* situation, especially to send out events for atomic commit operations.
+ *
+ * Care should be taken to avoid stale timestamps. If:
+ * - your driver has vblank support (i.e. dev->num_crtcs > 0)
+ * - the vblank irq is off (i.e. no one called drm_crtc_vblank_get)
+ * - from the vblank code's pov the pipe is still running (i.e. not
+ * in-between a drm_crtc_vblank_off()/on() pair)
+ * If all of these conditions hold then drm_crtc_send_vblank_event is
+ * going to give you a garbage timestamp and and sequence number (the last
+ * recorded before the irq was disabled). If you call drm_crtc_vblank_get/put
+ * around it, or after vblank_off, then either of those will have rolled things
+ * forward for you.
+ * So, drivers should call drm_crtc_vblank_off() before this function in their
+ * crtc atomic_disable handlers.
*/
void drm_crtc_send_vblank_event(struct drm_crtc *crtc,
struct drm_pending_vblank_event *e)
@@ -925,8 +938,12 @@ void drm_crtc_send_vblank_event(struct drm_crtc *crtc,
struct drm_device *dev = crtc->dev;
u64 seq;
unsigned int pipe = drm_crtc_index(crtc);
+ struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
ktime_t now;
+ WARN_ONCE(dev->num_crtcs > 0 && !vblank->enabled && !vblank->inmodeset,
+ "sending stale vblank info\n");
+
if (dev->num_crtcs > 0) {
seq = drm_vblank_count_and_time(dev, pipe, &now);
} else {
--
2.18.0
next prev parent reply other threads:[~2019-06-25 18:02 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-25 17:59 [PATCH v3 0/4] handle vblank when disabling ctc with interrupt disabled (was [PATCH v2] drm/imx: correct order of crtc disable) Robert Beckett
2019-06-25 17:59 ` Robert Beckett [this message]
2019-06-25 20:00 ` [PATCH v3 1/4] drm/vblank: warn on sending stale event Daniel Vetter
2019-06-25 20:02 ` Daniel Vetter
2019-06-25 17:59 ` [PATCH v3 2/4] drm/imx: notify drm core before sending event during crtc disable Robert Beckett
2019-06-25 20:03 ` Daniel Vetter
2019-06-25 17:59 ` [PATCH v3 3/4] drm/vblank: estimate vblank while disabling vblank if interrupt disabled Robert Beckett
2019-06-25 20:11 ` Daniel Vetter
2019-06-26 13:27 ` Ville Syrjälä
2019-06-26 14:30 ` Daniel Vetter
2019-06-25 17:59 ` [PATCH v3 4/4] drm/imx: only send event on crtc disable if kept disabled Robert Beckett
2019-06-25 20:22 ` Daniel Vetter
2019-06-26 8:33 ` Philipp Zabel
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