Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752797AbdFVIRy (ORCPT ); Thu, 22 Jun 2017 04:17:54 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:56026 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752621AbdFVIRu (ORCPT ); Thu, 22 Jun 2017 04:17:50 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org CCE26609A1 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=architt@codeaurora.org Subject: Re: [PATCH 1/7] drm/bridge: Support hotplugging panel-bridge. To: Benjamin Gaignard , Eric Anholt Cc: "dri-devel@lists.freedesktop.org" , Andrzej Hajda , Laurent Pinchart , Thierry Reding , Rob Herring , Mark Rutland , devicetree@vger.kernel.org, Linux Kernel Mailing List , Philippe Cornu , Boris Brezillon , Andrzej Hajda References: <20170615204130.19255-1-eric@anholt.net> <20170615204130.19255-2-eric@anholt.net> <777ee1b1-e5ce-ea29-8a48-f792354a22d1@codeaurora.org> <871sqkouvr.fsf@eliezer.anholt.net> <8e148170-b626-b426-3c94-b93d2746f4ce@codeaurora.org> <871sqe7ei0.fsf@eliezer.anholt.net> From: Archit Taneja Message-ID: Date: Thu, 22 Jun 2017 13:47:43 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3205 Lines: 77 On 06/22/2017 01:20 PM, Benjamin Gaignard wrote: > 2017-06-20 19:31 GMT+02:00 Eric Anholt : >> Archit Taneja writes: >> >>> On 06/16/2017 08:13 PM, Eric Anholt wrote: >>>> Archit Taneja writes: >>>> >>>>> On 06/16/2017 02:11 AM, Eric Anholt wrote: >>>>>> If the panel-bridge is being set up after the drm_mode_config_reset(), >>>>>> then the connector's state would never get initialized, and we'd >>>>>> dereference the NULL in the hotplug path. We also need to register >>>>>> the connector, so that userspace can get at it. >>>>>> >>>>> >>>>> Shouldn't the KMS driver make sure the panel-bridge is set up before >>>>> drm_mode_config_reset? Is it the case when we're inserting the >>>>> panel-bridge driver as a module? >>>>> >>>>> >>>>> All the connectors that have been added are registered automatically >>>>> when drm_dev_register() is called by the KMS driver. Registering a >>>>> connector in the middle of setting up our driver is prone to race >>>>> conditions if the userspace decides to use them immediately. >>>> >>>> Yeah, this is fixing initializing panel_bridge at DSI host_attach time, >>>> which in the case of a panel module that creates the DSI device >>>> (adv7533-style, like you said I should use as a reference) will be after >>>> drm_mode_config_reset() and drm_dev_register(). >>> >>> Okay. In the case of the msm kms driver, we defer probe until the >>> adv7533 module is inserted, only then we proceed to drm_mode_config_reset() >>> and drm_dev_register(). I assumed this was the general practice followed by >>> most kms drivers. I.,e the kms driver defers probe until all connector >>> related modules are inserted, and only then proceed to create a drm device. >> >> The problem, though, is the panel driver needs the MIPI DSI host to >> exist to call mipi_dsi_device_register_full() during the probe process. >> The adv7533 driver gets around this by registering the DSI device in the >> bridge attach step, but drm_panel doesn't have an attach step. I'm not sure how we can get around this. We had discussion about this on irc recently, but couldn't come up with a good conclusion. We could come up with a panel_attach() callback to make it similar to bridges, but that's just us avoiding the real issue. >> >> Another alternative is my original version of the panel driver that was >> a mipi_dsi_device driver that registered the panel during the DSI device >> probe. That's why vc4's panel lookup is during the MIPI DSI attach >> phase, currently. > This would require you to have a DSI device node in DT, rather than an i2c node, right? I don't know if we should do that because of a limitation in our drm_mipi_dsi and drm_panel frameworks. Does anyone have better ideas? Thanks, Archit > + Philippe in copy because we have the same probing issue when adding > panel-bridge > with the dsi bridge > >> >> _______________________________________________ >> dri-devel mailing list >> dri-devel@lists.freedesktop.org >> https://lists.freedesktop.org/mailman/listinfo/dri-devel >> -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project