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 D28C9D6E2AF for ; Thu, 18 Dec 2025 16:33:50 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 58EDB10EA6E; Thu, 18 Dec 2025 16:33:50 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=lankhorst.se header.i=@lankhorst.se header.b="Uli2II1Q"; dkim-atps=neutral Received: from lankhorst.se (lankhorst.se [141.105.120.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id F23D810EA60; Thu, 18 Dec 2025 16:33:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lankhorst.se; s=default; t=1766075626; bh=f44xvmNK/RAy/n5l5tS2hKEJu3wMpEA5Coc24G8mJc4=; h=From:To:Subject:Date:In-Reply-To:References:From; b=Uli2II1Q33XjpSlkCfEol9s28KGe41Hp6gORNaz12Q2WkgACeVnDw6Bss0m1Eu6T5 PJPvb1w7gdGO8O1SuFSC7JmlXUwu6wgk5UugNeCSl3+9isZZaKrgma+mE/h2ZaMiul Kh3rYTPxP8X8o04Z8sql459WKn7LHqQrPSywbiRzFlS5Bih2Bi2A8nPstEALezqCtS RUoJXOVohyLuqbzzOOzyZIMHE1Bxv52n/ezs7eUcMm2Cgie5dOwfwAbyg/dcgq7g65 VqiNvrdMzaVlcBMTOGitqBC8mLxKAK5Ogjs+pEzVMxKI9PcVrc3sjHVl3BxPg1FeWf txtexPQOcCmtA== From: Maarten Lankhorst To: intel-xe@lists.freedesktop.org, intel-gfx@lists.freedesktop.org Subject: [i915-rt v4 10/20] drm/i915: Use preempt_disable/enable_rt() where recommended Date: Thu, 18 Dec 2025 17:33:58 +0100 Message-ID: <20251218163408.97508-11-dev@lankhorst.se> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251218163408.97508-1-dev@lankhorst.se> References: <20251218163408.97508-1-dev@lankhorst.se> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" 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 --- 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 d700fd04cb407..a98dd3a436c28 100644 --- a/drivers/gpu/drm/i915/display/intel_vblank.c +++ b/drivers/gpu/drm/i915/display/intel_vblank.c @@ -317,6 +317,20 @@ static void intel_vblank_section_exit(struct intel_display *display) struct drm_i915_private *i915 = to_i915(display->drm); spin_unlock(&i915->uncore.lock); } + +static void intel_vblank_section_enter_irqf(struct intel_display *display, unsigned long *flags) + __acquires(i915->uncore.lock) +{ + struct drm_i915_private *i915 = to_i915(display->drm); + spin_lock_irqsave(&i915->uncore.lock, *flags); +} + +static void intel_vblank_section_exit_irqf(struct intel_display *display, unsigned long flags) + __releases(i915->uncore.lock) +{ + struct drm_i915_private *i915 = to_i915(display->drm); + spin_unlock_irqrestore(&i915->uncore.lock, flags); +} #else static void intel_vblank_section_enter(struct intel_display *display) { @@ -325,6 +339,17 @@ 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, @@ -361,10 +386,10 @@ 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) @@ -428,10 +453,10 @@ 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 @@ -469,13 +494,11 @@ 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