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Received: from mailgw02.mediatek.com ([216.200.240.185]) by casper.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1h3zuG-0006mi-Mg; Wed, 13 Mar 2019 09:10:39 +0000 X-UUID: e550b1a2f4a243d4b134654043f665c0-20190313 X-UUID: e550b1a2f4a243d4b134654043f665c0-20190313 Received: from mtkcas68.mediatek.inc [(172.29.94.19)] by mailgw02.mediatek.com (envelope-from ) (musrelay.mediatek.com ESMTP with TLS) with ESMTP id 939421133; Wed, 13 Mar 2019 01:08:28 -0800 Received: from MTKMBS31N2.mediatek.inc (172.27.4.87) by MTKMBS62N2.mediatek.inc (172.29.193.42) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Wed, 13 Mar 2019 02:08:26 -0700 Received: from MTKCAS32.mediatek.inc (172.27.4.184) by MTKMBS31N2.mediatek.inc (172.27.4.87) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Wed, 13 Mar 2019 17:08:23 +0800 Received: from [10.17.3.153] (172.27.4.253) by MTKCAS32.mediatek.inc (172.27.4.170) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Wed, 13 Mar 2019 17:08:23 +0800 Message-ID: <1552468103.7433.11.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 Date: Wed, 13 Mar 2019 17:08:23 +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> <1551278000.17917.50.camel@mhfsdcap03> X-Mailer: Evolution 3.2.3-0ubuntu6 MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190313_091037_121637_B947E039 X-CRM114-Status: GOOD ( 46.57 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: youlin.pei@mediatek.com, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Nicolas Boichat , Arnd Bergmann , srv_heupstream@mediatek.com, Greg Kroah-Hartman , Joerg Roedel , Will Deacon , LKML , Tomasz Figa , iommu@lists.linux-foundation.org, Rob Herring , linux-mediatek@lists.infradead.org, Matthias Brugger , yingjoe.chen@mediatek.com, Robin Murphy , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 2019-03-12 at 16:17 -0700, Evan Green wrote: > On Tue, Mar 12, 2019 at 7:21 AM Matthias Brugger wrote: > > > > > > > > On 05/03/2019 20:03, Evan Green wrote: > > > On Wed, Feb 27, 2019 at 6:33 AM Yong Wu wrote: > > >> > > >> 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. > > > > > > It seems like Robin had some suggestions about using > > > mtk_iommu_add_device() rather than the attach_dev() to set the links > > > up, and then track them for removal in the corresponding > > > remove_device() callback. Then you wouldn't need this change, right? Hi Evan, sorry for reply you so late. I have not got time to try this(Put it in the add_device), But I guess it works. At that time the ref_cnt here should be 1, then this patch is unnecessary. > > > > > > > FYI, Evan the patch is queued for v5.1-rc1 as > > 0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO flag") > > > > So if you think there is something wrong with it, then please provide a fix or > > raise awareness :) > > Oh. Thanks for the heads-up Matthias. It's pretty weird that we have > the kref there whose count we just completely ignore. I'll try to find > some time to submit a patch. Thanks very much if you improve this. > -Evan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel