From patchwork Tue Dec 14 14:02:57 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: 12676109 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 62E83C433F5 for ; Tue, 14 Dec 2021 14:03:32 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 8744210E4C6; Tue, 14 Dec 2021 14:03:13 +0000 (UTC) Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by gabe.freedesktop.org (Postfix) with ESMTPS id A627210E455; Tue, 14 Dec 2021 14:03:11 +0000 (UTC) From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1639490589; 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=ojUQOHApDdOULcoyUp+VYtjZvFRJbzhx7Iz5Y5kJCcY=; b=NevLdg4+xQ8xysT7CQWBdF4L5YJ1/ZOeNm08mMS8DHmpakVm1zLJNqvSndg65UIH5dTJ7P W1d6E8sv+94reRTTX9U5moA5NLYW+C9WO4XYytTvoha7cpB+dyeFjS6ToobN5Mhzw22CWX S4n9rB+3uJEA/ZpSjnXXKFgKYqYXaIA8ee0cYRIjy5NMkNuDgFhmU803mQMpLOQIO2ZrMT M+7t3ox3WpwlcpeD2U8/ygMyQg1UxDgaVSNpH9whzBHq9Lv+glSE7RuvTvV2JQiDYL51td RGoFl2LmtvvoMvWfX3B22jegRX5YaYhLYJmHaCTvxGxd8MgITci8EFMd+nDoYA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1639490589; 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=ojUQOHApDdOULcoyUp+VYtjZvFRJbzhx7Iz5Y5kJCcY=; b=qIoK8soBTdFdIXS2U93x/AssrK/xG0zvxwyP+bPmApVCK+LjWGJC+62QptRY0VL1Xlya9A g2KjS3ih2m/5PVAg== To: dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org Subject: [PATCH 4/8] drm/i915: Use preempt_disable/enable_rt() where recommended Date: Tue, 14 Dec 2021 15:02:57 +0100 Message-Id: <20211214140301.520464-5-bigeasy@linutronix.de> In-Reply-To: <20211214140301.520464-1-bigeasy@linutronix.de> References: <20211214140301.520464-1-bigeasy@linutronix.de> MIME-Version: 1.0 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: , Cc: Tvrtko Ursulin , David Airlie , Sebastian Andrzej Siewior , Mike Galbraith , Rodrigo Vivi , Thomas Gleixner 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 --- 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 038a9ec563c10..8e9ff0bcbc7e4 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);