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 936CAC4332F for ; Thu, 8 Dec 2022 12:37:27 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9FBCB10E21D; Thu, 8 Dec 2022 12:37:26 +0000 (UTC) Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by gabe.freedesktop.org (Postfix) with ESMTPS id DB7CA10E21D for ; Thu, 8 Dec 2022 12:37:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1670503041; x=1702039041; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=8EJdmX3Hyv8PMHDwRRG2W4ckgXjk9FruN7TQWNnGmuc=; b=ZydDqMQZN7Yl0ORO/MEDWwN4TRXJVgdgr/O5dge3+BVw79zIkKk46jZe MrObVOZBYUf91ErNJcMfPvptg7abgZ6V/K4nZS2QpPcfstfoXzYp5iEnN tN8ZewLnp9WMD3ky1UpXd/SJ8wGZ4cc+zbhIOPbaU3l9w5hDWDeMe7cV0 W6/2AXPLtSDkSyHhsSyz/Qdv7O76hUENR0ezPFEfH4ByFvaQ2UNqvdx3C /lF25XRDR1ruY7UHFKFiowqn85wgpB3JPH6mXfhn3iel1bcwNLTH4gpEo slb46yN1/xSgL4fkJ2YiJve1TCMrugKFahhU9Z3hLZCD+MZA7PvwPfgp+ g==; X-IronPort-AV: E=McAfee;i="6500,9779,10554"; a="300572199" X-IronPort-AV: E=Sophos;i="5.96,227,1665471600"; d="scan'208";a="300572199" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2022 04:37:21 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10554"; a="710448822" X-IronPort-AV: E=Sophos;i="5.96,227,1665471600"; d="scan'208";a="710448822" Received: from danyang-mobl.ccr.corp.intel.com (HELO localhost) ([10.252.18.245]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2022 04:37:18 -0800 From: Jani Nikula To: Andrzej Hajda , intel-gfx@lists.freedesktop.org In-Reply-To: <877cz213fa.fsf@intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20221208111217.3734461-1-andrzej.hajda@intel.com> <877cz213fa.fsf@intel.com> Date: Thu, 08 Dec 2022 14:37:16 +0200 Message-ID: <874ju6137n.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Intel-gfx] [PATCH 1/2] drm/i915/display: use fetch_and_zero if applicable 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: , Cc: Andrzej Hajda , Rodrigo Vivi Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Thu, 08 Dec 2022, Jani Nikula wrote: > On Thu, 08 Dec 2022, Andrzej Hajda wrote: >> Simplify the code. > > Personally, I absolutely hate fetch_and_zero(). > > I understand the point, but there are two main traps: > > First, the name implies atomicity, which there is none at all. > > Second, the name implies it's part of a kernel core header, which it > isn't, and this just amplifies the first point. > > It's surprising and misleading, and those are not things I like about > interfaces in the kernel. > > I would not like to see this proliferate. If fetch_and_zero() was atomic > *and* part of a core kernel header, it would be a different matter. But > I don't think that's going to happen, exactly because it won't be atomic > and the name implies it is. PS. The origin is commit 78ef2d9abad6 ("drm/i915: Add fetch_and_zero() macro") which presents the idea of making it a pattern that can be extended for atomic use, but six years and counting, that never happened. > > > BR, > Jani. > > >> >> Signed-off-by: Andrzej Hajda >> --- >> drivers/gpu/drm/i915/display/intel_hotplug.c | 12 ++++-------- >> 1 file changed, 4 insertions(+), 8 deletions(-) >> >> diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.c b/drivers/gpu/drm/i915/display/intel_hotplug.c >> index 907ab7526cb478..2972d7533da44e 100644 >> --- a/drivers/gpu/drm/i915/display/intel_hotplug.c >> +++ b/drivers/gpu/drm/i915/display/intel_hotplug.c >> @@ -304,10 +304,8 @@ static void i915_digport_work_func(struct work_struct *work) >> u32 old_bits = 0; >> >> spin_lock_irq(&dev_priv->irq_lock); >> - long_port_mask = dev_priv->display.hotplug.long_port_mask; >> - dev_priv->display.hotplug.long_port_mask = 0; >> - short_port_mask = dev_priv->display.hotplug.short_port_mask; >> - dev_priv->display.hotplug.short_port_mask = 0; >> + long_port_mask = fetch_and_zero(&dev_priv->display.hotplug.long_port_mask); >> + short_port_mask = fetch_and_zero(&dev_priv->display.hotplug.short_port_mask); >> spin_unlock_irq(&dev_priv->irq_lock); >> >> for_each_intel_encoder(&dev_priv->drm, encoder) { >> @@ -379,10 +377,8 @@ static void i915_hotplug_work_func(struct work_struct *work) >> >> spin_lock_irq(&dev_priv->irq_lock); >> >> - hpd_event_bits = dev_priv->display.hotplug.event_bits; >> - dev_priv->display.hotplug.event_bits = 0; >> - hpd_retry_bits = dev_priv->display.hotplug.retry_bits; >> - dev_priv->display.hotplug.retry_bits = 0; >> + hpd_event_bits = fetch_and_zero(&dev_priv->display.hotplug.event_bits); >> + hpd_retry_bits = fetch_and_zero(&dev_priv->display.hotplug.retry_bits); >> >> /* Enable polling for connectors which had HPD IRQ storms */ >> intel_hpd_irq_storm_switch_to_polling(dev_priv); -- Jani Nikula, Intel Open Source Graphics Center