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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 41628EB1062 for ; Tue, 10 Mar 2026 11:57:42 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9973010E6B1; Tue, 10 Mar 2026 11:57:30 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=lankhorst.se header.i=@lankhorst.se header.b="OUHFlH+e"; dkim-atps=neutral Received: from lankhorst.se (unknown [141.105.120.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id D004110E6AB; Tue, 10 Mar 2026 11:57:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lankhorst.se; s=default; t=1773143847; bh=42xBVBf7/zSvWegansEjJVb5Z73iPoTA1jQMjnntQyE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OUHFlH+ensq12c1ohduWSgHdyRcwBbpRnSJ8pRLmWMkGqRsdCWApbk7Cd6k/Z/mlY N96DTFE5xNoIzAQAhc4FOFo+0cy9ioDo7VaIzrtzjH2G2iVm1R009IIfS1axvEldEp kCwZbF9fB4Cl4yGQQjcbkdwAEbMJm1wh10ynfBaYePqyJKAk58DGLQdCHzdw0Iw5cz 4qeBOpwudAeNpKdzc4vmtjV8/oDvjzxO+gkKENMNE38Smwe6F4CkfB3oyCnR1Omqxi XlvzyF0kHAeodaQMivw8ml6aQ8nBPs4rxxCmgSG4Xlw5iajg93rX3HMoz6PYyI95QD SIKuvwNdkyzMQ== From: Maarten Lankhorst To: intel-xe@lists.freedesktop.org, intel-gfx@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org, Mike Galbraith , Mario Kleiner , Thomas Gleixner , Sebastian Andrzej Siewior , Maarten Lankhorst , Uma Shankar Subject: [PATCH v7 08/26] drm/i915: Use preempt_disable/enable_rt() where recommended Date: Tue, 10 Mar 2026 12:56:50 +0100 Message-ID: <20260310115709.2276203-9-dev@lankhorst.se> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260310115709.2276203-1-dev@lankhorst.se> References: <20260310115709.2276203-1-dev@lankhorst.se> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" From: Mike Galbraith Mario Kleiner suggest in commit ad3543ede630f ("drm/intel: Push get_scanout_position() timestamping into kms driver.") a spots where preemption should be disabled on PREEMPT_RT. The difference is that on PREEMPT_RT the intel_uncore::lock disables neither preemption nor interrupts and so region remains preemptible. The area covers only register reads and writes. The part that worries me is: - __intel_get_crtc_scanline() the worst case is 100us if no match is found. - intel_crtc_scanlines_since_frame_timestamp() not sure how long this may take in the worst case. It was in the RT queue for a while and nobody complained. Disable preemption on PREEPMPT_RT during timestamping. [bigeasy: patch description.] Cc: Mario Kleiner Signed-off-by: Mike Galbraith Signed-off-by: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Maarten Lankhorst Reviewed-by: Uma Shankar --- drivers/gpu/drm/i915/display/intel_vblank.c | 43 ++++++++++++++++----- 1 file changed, 33 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c index 3eb6418723a84..8263cefaa0fb6 100644 --- a/drivers/gpu/drm/i915/display/intel_vblank.c +++ b/drivers/gpu/drm/i915/display/intel_vblank.c @@ -316,6 +316,20 @@ static void intel_vblank_section_exit(struct intel_display *display) struct intel_uncore *uncore = to_intel_uncore(display->drm); spin_unlock(&uncore->lock); } + +static void intel_vblank_section_enter_irqf(struct intel_display *display, unsigned long *flags) + __acquires(i915->uncore.lock) +{ + struct intel_uncore *uncore = to_intel_uncore(display->drm); + spin_lock_irqsave(&uncore->lock, *flags); +} + +static void intel_vblank_section_exit_irqf(struct intel_display *display, unsigned long flags) + __releases(i915->uncore.lock) +{ + struct intel_uncore *uncore = to_intel_uncore(display->drm); + spin_unlock_irqrestore(&uncore->lock, flags); +} #else static void intel_vblank_section_enter(struct intel_display *display) { @@ -324,6 +338,17 @@ static void intel_vblank_section_enter(struct intel_display *display) static void intel_vblank_section_exit(struct intel_display *display) { } + +static void intel_vblank_section_enter_irqf(struct intel_display *display, unsigned long *flags) +{ + *flags = 0; +} + +static void intel_vblank_section_exit_irqf(struct intel_display *display, unsigned long flags) +{ + if (flags) + return; +} #endif static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc, @@ -360,10 +385,10 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc, * timing critical raw register reads, potentially with * preemption disabled, so the following code must not block. */ - local_irq_save(irqflags); - intel_vblank_section_enter(display); + intel_vblank_section_enter_irqf(display, &irqflags); - /* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_disable(); /* Get optional system timestamp before query. */ if (stime) @@ -427,10 +452,10 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc, if (etime) *etime = ktime_get(); - /* preempt_enable_rt() should go right here in PREEMPT_RT patchset. */ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable(); - intel_vblank_section_exit(display); - local_irq_restore(irqflags); + intel_vblank_section_exit_irqf(display, irqflags); /* * While in vblank, position will be negative @@ -468,13 +493,11 @@ int intel_get_crtc_scanline(struct intel_crtc *crtc) unsigned long irqflags; int position; - local_irq_save(irqflags); - intel_vblank_section_enter(display); + intel_vblank_section_enter_irqf(display, &irqflags); position = __intel_get_crtc_scanline(crtc); - intel_vblank_section_exit(display); - local_irq_restore(irqflags); + intel_vblank_section_exit_irqf(display, irqflags); return position; } -- 2.51.0