From patchwork Tue Oct 26 11:40:56 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 12584663 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D22CC433F5 for ; Tue, 26 Oct 2021 11:41:29 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id EA50060C4B for ; Tue, 26 Oct 2021 11:41:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org EA50060C4B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id DF2F86E591; Tue, 26 Oct 2021 11:41:10 +0000 (UTC) Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by gabe.freedesktop.org (Postfix) with ESMTPS id BEE366E51C; Tue, 26 Oct 2021 11:41:08 +0000 (UTC) From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1635248466; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NZdup3Ji8kBPGkW4RTEx9y7VueR9SxIvsPT7p9xwNuY=; b=kWXJEEABd63YMQRTEdZn9rxlDREQnomUdn75nKlOluEGF3QoMs9lKTc7/96i7wTj/2QA5Q KA0FjN+g+eESfK0G4+dWSw8GK94uICZGjvYSGMXOgyMjubIY3pSPMVHTEuUW5j0gesnxOU LFqvISgc6E9o+Yp6L1sZeO2wj3IRuavnwGOYdM8kb1kxaklrbFkYIJtJq2Kh/FPH245rTy ldQT3CEoOuCL8/+1s4fU4mCMI72CTK9UY1gFUvbjzimYaOn+iiGhwbQ3OLYA8HfIeFCYq9 VAsbiwVTQYFFgpgO6IfGoaE71/kUIGGFFx2U6IyyORaYwuctbys8T6vfnlBjLQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1635248466; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NZdup3Ji8kBPGkW4RTEx9y7VueR9SxIvsPT7p9xwNuY=; b=CceJB0gqJM1PtHm1ogbWxKBoFyCM5MZaIwHglwwQ6FiFn+mXb06wWONzGqCi3dAjgDlTlA POdcBrwwB0XwDzBQ== To: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org Cc: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , Thomas Gleixner , Peter Zijlstra , Mike Galbraith , Mario Kleiner , Sebastian Andrzej Siewior Date: Tue, 26 Oct 2021 13:40:56 +0200 Message-Id: <20211026114100.2593433-6-bigeasy@linutronix.de> In-Reply-To: <20211026114100.2593433-1-bigeasy@linutronix.de> References: <20211026114100.2593433-1-bigeasy@linutronix.de> MIME-Version: 1.0 Subject: [Intel-gfx] [PATCH 5/9] drm/i915: Use preempt_disable/enable_rt() where recommended 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 --- drivers/gpu/drm/i915/i915_irq.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c index 77680bca46eec..be8faaaa60226 100644 --- a/drivers/gpu/drm/i915/i915_irq.c +++ b/drivers/gpu/drm/i915/i915_irq.c @@ -916,7 +916,8 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc, */ spin_lock_irqsave(&dev_priv->uncore.lock, 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) @@ -980,7 +981,8 @@ 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(); spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);