Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752081AbdHDWT5 (ORCPT ); Fri, 4 Aug 2017 18:19:57 -0400 Received: from mail-qk0-f176.google.com ([209.85.220.176]:38902 "EHLO mail-qk0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751303AbdHDWT4 (ORCPT ); Fri, 4 Aug 2017 18:19:56 -0400 MIME-Version: 1.0 In-Reply-To: <87zibfqd1u.fsf@eliezer.anholt.net> References: <20170718210510.12229-1-eric@anholt.net> <20170718210510.12229-2-eric@anholt.net> <2023170.2CE3xBA9bq@avalon> <87zibfqd1u.fsf@eliezer.anholt.net> From: Ilia Mirkin Date: Fri, 4 Aug 2017 18:19:55 -0400 X-Google-Sender-Auth: rYxfb0EM8zOZGL1GrlSGmcA-GIQ Message-ID: Subject: Re: [PATCH v5 2/6] drm/bridge: Add a devm_ allocator for panel bridge. To: Eric Anholt Cc: Laurent Pinchart , "dri-devel@lists.freedesktop.org" , Archit Taneja , Andrzej Hajda , Thierry Reding , "linux-kernel@vger.kernel.org" , Daniel Vetter Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1442 Lines: 32 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.