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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8112C43381 for ; Wed, 27 Feb 2019 14:34:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C2F7E213A2 for ; Wed, 27 Feb 2019 14:34:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730746AbfB0OeL (ORCPT ); Wed, 27 Feb 2019 09:34:11 -0500 Received: from Mailgw01.mediatek.com ([1.203.163.78]:27457 "EHLO mailgw01.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726866AbfB0OeK (ORCPT ); Wed, 27 Feb 2019 09:34:10 -0500 X-UUID: 986e6f0e674e4a369015d4b8e0b45207-20190227 X-UUID: 986e6f0e674e4a369015d4b8e0b45207-20190227 Received: from mtkcas36.mediatek.inc [(172.27.4.253)] by mailgw01.mediatek.com (envelope-from ) (mailgw01.mediatek.com ESMTP with TLS) with ESMTP id 357067242; Wed, 27 Feb 2019 22:33:56 +0800 Received: from MTKCAS36.mediatek.inc (172.27.4.186) by MTKMBS31N2.mediatek.inc (172.27.4.87) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Wed, 27 Feb 2019 22:33:55 +0800 Received: from [10.17.3.153] (172.27.4.253) by MTKCAS36.mediatek.inc (172.27.4.170) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Wed, 27 Feb 2019 22:33:54 +0800 Message-ID: <1551278034.17917.52.camel@mhfsdcap03> Subject: Re: [PATCH 03/13] iommu/mediatek: Add probe_defer for smi-larb From: Yong Wu To: Evan Green CC: , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Nicolas Boichat , Arnd Bergmann , , Greg Kroah-Hartman , Joerg Roedel , Will Deacon , LKML , Tomasz Figa , , Rob Herring , , Matthias Brugger , , Robin Murphy , Date: Wed, 27 Feb 2019 22:33:54 +0800 In-Reply-To: References: <1546318276-18993-1-git-send-email-yong.wu@mediatek.com> <1546318276-18993-4-git-send-email-yong.wu@mediatek.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit MIME-Version: 1.0 X-MTK: N Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2019-02-25 at 15:54 -0800, Evan Green wrote: > On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote: > > > > The iommu consumer should use device_link to connect with the > > smi-larb(supplier). then the smi-larb should run before the iommu > > consumer. Here we delay the iommu driver until the smi driver is > > ready, then all the iommu consumer always is after the smi driver. > > > > When there is no this patch, if some consumer drivers run before > > smi-larb, the supplier link_status is DL_DEV_NO_DRIVER(0) in the > > device_link_add, then device_links_driver_bound will use WARN_ON > > to complain that the link_status of supplier is not right. > > > > I don't quite have enough knowledge of device links to figure out if > this is a) the right fix, b) a deficiency in the device_links code, or > c) neither. I can not say more about the device link, But from the MTK iommu point of view, it looks a right fix. As the comment above, we should make sure the probe sequence, SMI-larb should be before MTK IOMMU which need be before iommu-consumer. this patch help SMI-larb always is before MTK_IOMMU. Then if there is no this patchset, what the MTK_IOMMU will happen?. The MTK_IOMMU is subsys_initcall, all the consume only need after the MTK_IOMMU and don't need wait for SMI-larb driver. If some consume run before SMI-larb driver, It also is OK while it don't call mtk_smi_larb_get in this probe.(Of course it will abort if it call this while smi-driver don't probe at that time). the consumer and smi-larb normally are module_init, we can not guarantee the the sequence. it is a potential issue. Some consume know it should wait for SMI-larb like [1], but It don't work. [1] https://elixir.bootlin.com/linux/v5.0-rc1/source/drivers/media/platform/mtk-mdp/mtk_mdp_comp.c#L145 > > Perhaps someone else could chime in on this one. > -Evan > > _______________________________________________ > Linux-mediatek mailing list > Linux-mediatek@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-mediatek