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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 4A849C4360F for ; Wed, 27 Feb 2019 14:33:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 256B42133D for ; Wed, 27 Feb 2019 14:33:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730703AbfB0Od3 (ORCPT ); Wed, 27 Feb 2019 09:33:29 -0500 Received: from Mailgw01.mediatek.com ([1.203.163.78]:54175 "EHLO mailgw01.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1730222AbfB0Od3 (ORCPT ); Wed, 27 Feb 2019 09:33:29 -0500 X-UUID: ce4db0ea793c41548216446ed4da2f96-20190227 X-UUID: ce4db0ea793c41548216446ed4da2f96-20190227 Received: from mtkcas34.mediatek.inc [(172.27.4.253)] by mailgw01.mediatek.com (envelope-from ) (mailgw01.mediatek.com ESMTP with TLS) with ESMTP id 1687198339; Wed, 27 Feb 2019 22:33:22 +0800 Received: from MTKCAS36.mediatek.inc (172.27.4.186) by MTKMBS31N1.mediatek.inc (172.27.4.69) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Wed, 27 Feb 2019 22:33:20 +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 22:33:20 +0800 Message-ID: <1551278000.17917.50.camel@mhfsdcap03> Subject: Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag From: Yong Wu To: Evan Green CC: Joerg Roedel , Greg Kroah-Hartman , Matthias Brugger , Rob Herring , Robin Murphy , Tomasz Figa , Will Deacon , , , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , LKML , , , Arnd Bergmann , , , Nicolas Boichat Date: Wed, 27 Feb 2019 22:33:20 +0800 In-Reply-To: References: <1546318276-18993-1-git-send-email-yong.wu@mediatek.com> <1546318276-18993-3-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 15:53 -0800, Evan Green wrote: > On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote: > > > > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > > automatically on consumer/supplier driver unbind", that means we should > > remove whole the device_link when there is no this driver no matter what > > the ref_count of the link is. > > > > CC: Greg Kroah-Hartman > > Signed-off-by: Yong Wu > > --- > > The ref_count of our device_link normally is over 1. When the consumer > > device driver is removed, whole the device_link should be removed. > > Thus, I add this patch. > > --- > > I will admit to reading about device links for the first time while > reviewing this patch, but I don't really get this. Why use a kref at > all if we're just going to ignore its value? For instance, I see that > if you call device_link_add() with the same supplier and consumer, it > uses the kref to return the same link. That machinery is broken with > your change. Although I don't see any uses of it, you might also > expect a supplier or consumer could do a kref_get() on the link it got > back from device_link_add(), and have a reasonable expectation that > the link wouldn't be freed out from under it. This would also be > broken. > > Can you explain why your device_links normally have a reference count > >1, I use device link between the smi-larb device and the iommu-consumer device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this patchset, we use device_link to link the VDEC device and the smi-larb1 device in the function(mtk_iommu_config). since there are 4 ports, it will call device_link_add 4 times. > > and why those additional references can't be cleaned up in an > orderly fashion? If the iommu-consume device(like VDEC above) is removed, It should enter device_links_driver_cleanup which only ref_put one time. I guess whole the link should be removed at that time. > > (To be honest, I don't really understand the case for the AUTOREMOVE > flags at all. Is there some case where the party that set up the link > can't tear it down? Or is this a way to devm_ify the link, where devm > itself doesn't work because the links themselves stall out that > mechanism?)