From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932124AbcITBgY (ORCPT ); Mon, 19 Sep 2016 21:36:24 -0400 Received: from regular1.263xmail.com ([211.150.99.132]:49020 "EHLO regular1.263xmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751119AbcITBgW (ORCPT ); Mon, 19 Sep 2016 21:36:22 -0400 X-263anti-spam: KSV:0;BIG:0;ABS:1;DNS:0;ATT:0;SPF:S; X-MAIL-GRAY: 0 X-MAIL-DELIVERY: 1 X-KSVirus-check: 0 X-ABS-CHECKED: 1 X-SKE-CHECKED: 1 X-ADDR-CHECKED4: 1 X-RL-SENDER: mark.yao@rock-chips.com X-FST-TO: djkurtz@chromium.org X-SENDER-IP: 103.29.142.67 X-LOGIN-NAME: mark.yao@rock-chips.com X-UNIQUE-TAG: <6ec4a283d4fadd7b32a4dbb97023165e> X-ATTACHMENT-NUM: 0 X-DNS-TYPE: 0 Subject: Re: [PATCH 2/8] drm/rockchip: Get rid of some unnecessary code To: Tomasz Figa References: <1473857701-9250-1-git-send-email-tfiga@chromium.org> <1473857701-9250-3-git-send-email-tfiga@chromium.org> <57DDF2EE.5060807@rock-chips.com> Cc: dri-devel , "linux-arm-kernel@lists.infradead.org" , "open list:ARM/Rockchip SoC..." , "linux-kernel@vger.kernel.org" , Heiko Stuebner , David Airlie , Sean Paul , Daniel Kurtz From: Mark yao Message-ID: <57E0928C.8080103@rock-chips.com> Date: Tue, 20 Sep 2016 09:36:12 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016年09月18日 12:01, Tomasz Figa wrote: > Hi Mark, > > On Sun, Sep 18, 2016 at 10:50 AM, Mark yao wrote: >> On 2016年09月14日 20:54, Tomasz Figa wrote: >>> Current code implements prepare_fb and cleanup_fb callbacks only to >>> grab/release fb references, which is already done by atomic framework >>> when creating/destryoing plane state. Let's remove these >>> unused bits. >>> >>> Signed-off-by: Tomasz Figa >>> --- >>> drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 18 ------------------ >>> 1 file changed, 18 deletions(-) >> >> Hi Tomasz >> >> I think we can't get rid of the prepare_fb and cleanup_fb > I think I have to disagree. Please see below for detailed explanation. > >> see the reason: >> commit 44d0237a26395ac94160cf23f32769013b365590 >> Author: Mark Yao >> Date: Fri Apr 29 11:37:20 2016 +0800 >> >> drm/rockchip: vop: fix iommu crash with async atomic >> >> After async atomic_commit callback, drm_atomic_clean_old_fb will >> clean all old fb, but because async, the old fb may be also on >> the vop hardware, dma will access the old fb buffer, clean old >> fb will cause iommu page fault. > I think the above is not quite right. Atomic plane state holds a > reference to its fb and old state is not supposed to be destroyed > until the flip completes. > > Indeed current rockchip_atomic_commit implementation has following > order of calls: rockchip_atomic_wait_for_complete(), > drm_atomic_helper_cleanup_planes(), drm_atomic_state_free(). This > means that .cleanup_fb() is called from > drm_atomic_helper_cleanup_planes() just before drm_atomic_state_free() > will release references by destroying old plane states. Note that both > are called already after rockchip_atomic_wait_for_complete(), so it > should be already safe to free the old fbs. > > So the above fix doesn't really do anything, possibly just covers the > race condition of the original wait for vblank function by delaying > drm_atomic_state_free() a bit. > > Moreover, the whole series has been thoroughly tested in Chrome OS 4.4 > kernel, including async commits. (There is still a possibility some > newer upstream changes slightly modified the semantics, but I couldn't > find such difference. Actually one of the advantages of atomic helpers > was to avoid manually refcounting the fbs from the driver.) > > Best regards, > Tomasz > Hi Tomasz You are right, plane_duplicate_state/plane_destroy_state already protect the old fbs. we can get rid of prepare_fb and cleanup_fb. -- Ｍark Yao