From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE266C48BD5 for ; Tue, 25 Jun 2019 18:02:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6C9C20883 for ; Tue, 25 Jun 2019 18:02:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732782AbfFYSCj (ORCPT ); Tue, 25 Jun 2019 14:02:39 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:58764 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727289AbfFYSCi (ORCPT ); Tue, 25 Jun 2019 14:02:38 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: bbeckett) with ESMTPSA id CE79E28A3F3 From: Robert Beckett To: dri-devel@lists.freedesktop.org Cc: Maarten Lankhorst , Maxime Ripard , Sean Paul , David Airlie , Daniel Vetter , Philipp Zabel , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Robert Beckett Subject: [PATCH v3 1/4] drm/vblank: warn on sending stale event Date: Tue, 25 Jun 2019 18:59:12 +0100 Message-Id: X-Mailer: git-send-email 2.18.0 In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Warn when about to send stale vblank info and add advice to documentation on how to avoid. Signed-off-by: Robert Beckett --- 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