From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Brugger Subject: Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag Date: Tue, 12 Mar 2019 15:21:51 +0100 Message-ID: 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Evan Green , Yong Wu Cc: Joerg Roedel , Greg Kroah-Hartman , Rob Herring , Robin Murphy , Tomasz Figa , Will Deacon , linux-mediatek@lists.infradead.org, srv_heupstream@mediatek.com, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , LKML , linux-arm-kernel@lists.infradead.org, iommu@lists.linux-foundation.org, Arnd Bergmann , yingjoe.chen@mediatek.com, youlin.pei@mediatek.com, Nicolas Boichat List-Id: devicetree@vger.kernel.org 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? > 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 :)