From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751434AbdHEK7h (ORCPT ); Sat, 5 Aug 2017 06:59:37 -0400 Received: from smtp.domeneshop.no ([194.63.252.55]:40647 "EHLO smtp.domeneshop.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751250AbdHEK7f (ORCPT ); Sat, 5 Aug 2017 06:59:35 -0400 Subject: Re: [PATCH v5 2/6] drm/bridge: Add a devm_ allocator for panel bridge. To: Ilia Mirkin , Eric Anholt Cc: Daniel Vetter , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Thierry Reding , Laurent Pinchart References: <20170718210510.12229-1-eric@anholt.net> <20170718210510.12229-2-eric@anholt.net> <2023170.2CE3xBA9bq@avalon> <87zibfqd1u.fsf@eliezer.anholt.net> From: =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= Message-ID: Date: Sat, 5 Aug 2017 12:59:07 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (I had to switch to Daniel's Intel address to get this sent) Den 05.08.2017 00.19, skrev Ilia Mirkin: > On Fri, Aug 4, 2017 at 4:43 PM, Eric Anholt wrote: >> Laurent Pinchart writes: >> >>> Hi Eric, >>> >>> (CC'ing Daniel) >>> >>> Thank you for the patch. >>> >>> On Tuesday 18 Jul 2017 14:05:06 Eric Anholt wrote: >>>> This will let drivers reduce the error cleanup they need, in >>>> particular the "is_panel_bridge" flag. >>>> >>>> v2: Slight cleanup of remove function by Andrzej >>> I just want to point out that, in the context of Daniel's work on hot-unplug, >>> 90% of the devm_* allocations are wrong and will get in the way. All DRM core >>> objects that are accessible one way or another from userspace will need to be >>> properly reference-counted and freed only when the last reference disappears, >>> which could be well after the corresponding device is removed. I believe this >>> could be one such objects :-/ >> Sure, if you're hotplugging, your life is pain. For non-hotpluggable >> devices, like our SOC platform devices (current panel-bridge consumers), >> this still seems like an excellent simplification of memory management. > At that point you may as well make your module non-unloadable, and > return failure when trying to remove a device from management by the > driver (whatever the opposite of "probe" is, I forget). Hotplugging > doesn't only happen when physically removing, it can happen for all > kinds of reasons... and userspace may still hold references in some of > those cases. If drm_open() gets a ref on dev->dev and puts it in drm_release(), won't that delay devm_* cleanup until userspace is done?