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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 76BC8C2BA19 for ; Mon, 6 Apr 2020 13:38:41 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 40DBF23356 for ; Mon, 6 Apr 2020 13:38:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="WRrwp38b" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 40DBF23356 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9E8DE6E095; Mon, 6 Apr 2020 13:38:40 +0000 (UTC) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by gabe.freedesktop.org (Postfix) with ESMTPS id D9C4D6E095; Mon, 6 Apr 2020 13:38:39 +0000 (UTC) Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2D4CA23356; Mon, 6 Apr 2020 13:38:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586180319; bh=CPlJ6V3ATvMiy7si9/NG3B9JHpu8lzufixuIa/M7hdQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=WRrwp38bcuvOSfVYPnOEwOVQ5zQcH/oQPW2fE+wwFQ5w/egh7ALFdzOlAb4EPg2Nk gDbaccrnYXpo2VNc2yb5EoiNroMos+Z+lLsuNcjgf790J+dfyboUYHqhkE3bgWyshY hqgt+LYFrQ9zIRoWMBfw3XzH0q3Qx1oUvlp4odss= Date: Mon, 6 Apr 2020 15:38:35 +0200 From: Greg Kroah-Hartman To: Daniel Vetter Subject: Re: [PATCH 01/44] drivers/base: Always release devres on device_del Message-ID: <20200406133835.GA24355@kroah.com> References: <20200403135828.2542770-1-daniel.vetter@ffwll.ch> <20200403135828.2542770-2-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel Vetter , Intel Graphics Development , DRI Development , "Rafael J. Wysocki" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Mon, Apr 06, 2020 at 02:32:51PM +0200, Daniel Vetter wrote: > On Fri, Apr 3, 2020 at 3:58 PM Daniel Vetter wrote: > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > also represents the userspace interfaces and has everything else > > dangling off it) init functions using devres, devm_drm_dev_init and > > soon devm_drm_dev_alloc (this patch series adds that). > > > > A slight trouble is that drm_device itself holds a reference on the > > struct device it's sitting on top (for sysfs links and dmesg debug and > > lots of other things), so there's a reference loop. For real drivers > > this is broken at remove/unplug time, where all devres resources are > > released device_release_driver(), before the final device reference is > > dropped. So far so good. > > > > There's 2 exceptions: > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > platform device to make them look more like normal devices to > > userspace. These aren't drivers in the driver model sense, we simple > > create a platform_device and register it. > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > the selftests aren't proper drivers in the driver model sense. > > > > For these two cases the reference loop isn't broken, because devres is > > only cleaned up when the last device reference is dropped. But that's > > not happening, because the drm_device holds that last struct device > > reference. > > > > Thus far this wasn't a problem since the above cases simply > > hand-rolled their cleanup code. But I want to convert all drivers over > > to the devm_ versions, hence it would be really nice if these > > virtual/fake/mock uses-cases could also be managed with devres > > cleanup. > > > > I see three possible approaches: > > Restarting this at the top level, because the discussion thus far just > ended in a long "you're doing it wrong", despite that I think we're > doing what v4l is doing (plus/minus that we can't do an exact matching > handling in drm because our uapi has a lot more warts, which we can't > change because no breaking userspace). > > So which one of the three below is the right approach? > > Aside, looking at the v4l solution I think there's also a confusion > about struct device representing a char device (which v4l directly > uses as its userspace interface refcounted thing, and which drm does > _not_ directly). And a struct device embedded into something like > platform_device or a virtual device, where a driver can bind to. My > question here is about the former, I don't care how cdev struct device > are cleaned up one bit. Now if other subsystems relies on the devres > cleanup behaviour we currently have because of such cdev usage, then > yeah first approach doesn't work (and I have a big surprised that use > case, but hey would actually learn something). > > End of aside, since again I want to figure out which of the tree > approaches it the right one. Not about how wrong one of them is, > ignoring the other three I laid out. And maybe there's even more > options for this. Sorry, been swamped with other things, give me a few days to get back to this, I need to dig into how you all are dealing with the virtual drivers. Doing this in the middle of the merge window is a bit rough :) thanks, greg k-h _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel 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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 CC874C2BA1B for ; Mon, 6 Apr 2020 13:38:43 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A2B2B23356 for ; Mon, 6 Apr 2020 13:38:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="WRrwp38b" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A2B2B23356 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 03CDD6E3BC; Mon, 6 Apr 2020 13:38:41 +0000 (UTC) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by gabe.freedesktop.org (Postfix) with ESMTPS id D9C4D6E095; Mon, 6 Apr 2020 13:38:39 +0000 (UTC) Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2D4CA23356; Mon, 6 Apr 2020 13:38:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586180319; bh=CPlJ6V3ATvMiy7si9/NG3B9JHpu8lzufixuIa/M7hdQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=WRrwp38bcuvOSfVYPnOEwOVQ5zQcH/oQPW2fE+wwFQ5w/egh7ALFdzOlAb4EPg2Nk gDbaccrnYXpo2VNc2yb5EoiNroMos+Z+lLsuNcjgf790J+dfyboUYHqhkE3bgWyshY hqgt+LYFrQ9zIRoWMBfw3XzH0q3Qx1oUvlp4odss= Date: Mon, 6 Apr 2020 15:38:35 +0200 From: Greg Kroah-Hartman To: Daniel Vetter Message-ID: <20200406133835.GA24355@kroah.com> References: <20200403135828.2542770-1-daniel.vetter@ffwll.ch> <20200403135828.2542770-2-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Subject: Re: [Intel-gfx] [PATCH 01/44] drivers/base: Always release devres on device_del X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel Vetter , Intel Graphics Development , DRI Development , "Rafael J. Wysocki" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Mon, Apr 06, 2020 at 02:32:51PM +0200, Daniel Vetter wrote: > On Fri, Apr 3, 2020 at 3:58 PM Daniel Vetter wrote: > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > also represents the userspace interfaces and has everything else > > dangling off it) init functions using devres, devm_drm_dev_init and > > soon devm_drm_dev_alloc (this patch series adds that). > > > > A slight trouble is that drm_device itself holds a reference on the > > struct device it's sitting on top (for sysfs links and dmesg debug and > > lots of other things), so there's a reference loop. For real drivers > > this is broken at remove/unplug time, where all devres resources are > > released device_release_driver(), before the final device reference is > > dropped. So far so good. > > > > There's 2 exceptions: > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > platform device to make them look more like normal devices to > > userspace. These aren't drivers in the driver model sense, we simple > > create a platform_device and register it. > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > the selftests aren't proper drivers in the driver model sense. > > > > For these two cases the reference loop isn't broken, because devres is > > only cleaned up when the last device reference is dropped. But that's > > not happening, because the drm_device holds that last struct device > > reference. > > > > Thus far this wasn't a problem since the above cases simply > > hand-rolled their cleanup code. But I want to convert all drivers over > > to the devm_ versions, hence it would be really nice if these > > virtual/fake/mock uses-cases could also be managed with devres > > cleanup. > > > > I see three possible approaches: > > Restarting this at the top level, because the discussion thus far just > ended in a long "you're doing it wrong", despite that I think we're > doing what v4l is doing (plus/minus that we can't do an exact matching > handling in drm because our uapi has a lot more warts, which we can't > change because no breaking userspace). > > So which one of the three below is the right approach? > > Aside, looking at the v4l solution I think there's also a confusion > about struct device representing a char device (which v4l directly > uses as its userspace interface refcounted thing, and which drm does > _not_ directly). And a struct device embedded into something like > platform_device or a virtual device, where a driver can bind to. My > question here is about the former, I don't care how cdev struct device > are cleaned up one bit. Now if other subsystems relies on the devres > cleanup behaviour we currently have because of such cdev usage, then > yeah first approach doesn't work (and I have a big surprised that use > case, but hey would actually learn something). > > End of aside, since again I want to figure out which of the tree > approaches it the right one. Not about how wrong one of them is, > ignoring the other three I laid out. And maybe there's even more > options for this. Sorry, been swamped with other things, give me a few days to get back to this, I need to dig into how you all are dealing with the virtual drivers. Doing this in the middle of the merge window is a bit rough :) thanks, greg k-h _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx