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 8D7C2C63703 for ; Thu, 8 Dec 2022 12:32:55 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id C1FAE10E21D; Thu, 8 Dec 2022 12:32:54 +0000 (UTC) Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9107E10E21D for ; Thu, 8 Dec 2022 12:32:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1670502769; x=1702038769; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=X+gCFy3mFBQyjIjuewUoMToKx/dXAqGtuzWm1Fl4TTM=; b=LHmiQrswN/gOlRUOA8txZcjVllDa3pfJzZ8hVGGoM4Sue0CznZ8jB1J0 j2I0R8LailQNU+3MOrCUn3UeokqnvtvDPT1wFUmm4RQrkriuFB4mdIZx5 OOtBtXHEYydlKmWxzGqKiEb7npl6kem51tgPLEF0IK2F69/zZNFKHni+M m2yRiob+HdgrbVKNlxjrUGF5GrZmH53zYuWlk3IoHU4O3X+TBpuZ/HhrZ vPxibEJsVdocZvRIxM1uPvLFlsgdXNY8UH5CQkU212XVeXko8B+HXe1Xy /I5Gc+UVrvNY/zuk8BzyE+Bqzi8UASY9prdUSKJ09AeJth9sRb0wOMY44 g==; X-IronPort-AV: E=McAfee;i="6500,9779,10554"; a="304790999" X-IronPort-AV: E=Sophos;i="5.96,227,1665471600"; d="scan'208";a="304790999" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2022 04:32:47 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10554"; a="640610151" X-IronPort-AV: E=Sophos;i="5.96,227,1665471600"; d="scan'208";a="640610151" Received: from danyang-mobl.ccr.corp.intel.com (HELO localhost) ([10.252.18.245]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2022 04:32:44 -0800 From: Jani Nikula To: Andrzej Hajda , intel-gfx@lists.freedesktop.org In-Reply-To: <20221208111217.3734461-1-andrzej.hajda@intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20221208111217.3734461-1-andrzej.hajda@intel.com> Date: Thu, 08 Dec 2022 14:32:41 +0200 Message-ID: <877cz213fa.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, 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. 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