From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751586AbdBXBzz (ORCPT ); Thu, 23 Feb 2017 20:55:55 -0500 Received: from szxga01-in.huawei.com ([45.249.212.187]:2841 "EHLO dggrg01-dlp.huawei.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751267AbdBXBzx (ORCPT ); Thu, 23 Feb 2017 20:55:53 -0500 Subject: Re: [RFC][PATCH] drm: kirin: Add a mutex to avoid fb initialization race To: John Stultz , lkml References: <1487811383-6915-1-git-send-email-john.stultz@linaro.org> CC: Rongrong Zou , Xinwei Kong , Chen Feng , "David Airlie" , Daniel Vetter , Sean Paul , From: liuxinliang Message-ID: <58AF92A3.2040200@hisilicon.com> Date: Fri, 24 Feb 2017 09:55:47 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: <1487811383-6915-1-git-send-email-john.stultz@linaro.org> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.46.116.1] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090203.58AF929B.00BD,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2014-11-16 11:51:01, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: d9f8332d6f1d91eafc558fe9ff26db3b Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi John, On 2017/2/23 8:56, John Stultz wrote: > In some cases I've been seeing a race where two framebuffers > would be initialized, as kirin_fbdev_output_poll_changed() > might get called quickly in succession, resulting in the fb > initialization happening twice. This could cause the system I might understand this race. This because two places call drm_helper_hpd_irq_event might cause the race: One place is here static int kirin_drm_kms_init(struct drm_device *dev) { ... /* force detection after connectors init */ (void)drm_helper_hpd_irq_event(dev); ... } another is the adv7533 interrupt thread handler static int adv7511_irq_process(struct adv7511 *adv7511, bool process_hpd) { ... if (process_hpd && irq0 & ADV7511_INT0_HPD && adv7511->bridge.encoder) drm_helper_hpd_irq_event(adv7511->connector.dev); ... } right? I don't get a better way to fix this yet , I like to put fb_lock into kirin_drm_private. And it seems hard to fix this in the core drm_helper_hpd_irq_event. -xinliang > to boot up with a blank screen. > > This patch adds a simple mutex to serialize it and seems to > avoid the race. > > Obviously I suspect this patch isn't the best solution, but > I wanted to send it out as something concrete to discuss the > bug. > > Suggestions or feedback for a better solution would be greatly > appreciated. > > Cc: Xinliang Liu > Cc: Rongrong Zou > Cc: Xinwei Kong > Cc: Chen Feng > Cc: David Airlie > Cc: Daniel Vetter > Cc: Sean Paul > Cc: dri-devel@lists.freedesktop.org > Signed-off-by: John Stultz > --- > drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c > index ebd5f4f..80c607f 100644 > --- a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c > +++ b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c > @@ -50,11 +50,13 @@ static int kirin_drm_kms_cleanup(struct drm_device *dev) > return 0; > } > > +static DEFINE_MUTEX(fb_lock); > #ifdef CONFIG_DRM_FBDEV_EMULATION > static void kirin_fbdev_output_poll_changed(struct drm_device *dev) > { > struct kirin_drm_private *priv = dev->dev_private; > > + mutex_lock(&fb_lock); > if (priv->fbdev) { > drm_fbdev_cma_hotplug_event(priv->fbdev); > } else { > @@ -64,6 +66,7 @@ static void kirin_fbdev_output_poll_changed(struct drm_device *dev) > if (IS_ERR(priv->fbdev)) > priv->fbdev = NULL; > } > + mutex_unlock(&fb_lock); > } > #endif >