From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751779AbdK3SpV (ORCPT ); Thu, 30 Nov 2017 13:45:21 -0500 Received: from mail.free-electrons.com ([62.4.15.54]:42534 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750769AbdK3SpT (ORCPT ); Thu, 30 Nov 2017 13:45:19 -0500 Subject: Re: [PATCH 0/5] PCI: Add support to the Cadence PCIe controller To: Lorenzo Pieralisi , Kishon Vijay Abraham I Cc: bhelgaas@google.com, linux-pci@vger.kernel.org, adouglas@cadence.com, stelford@cadence.com, dgary@cadence.com, kgopi@cadence.com, eandrews@cadence.com, thomas.petazzoni@free-electrons.com, sureshp@cadence.com, nsekhar@ti.com, linux-kernel@vger.kernel.org, robh@kernel.org, devicetree@vger.kernel.org References: <20171128155039.GA17154@red-moon> <8c6c50fc-47a9-7b93-d826-1dba9c4d09c2@ti.com> <20171130181819.GD12096@red-moon> From: Cyrille Pitchen Message-ID: Date: Thu, 30 Nov 2017 19:45:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171130181819.GD12096@red-moon> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, Le 30/11/2017 à 19:18, Lorenzo Pieralisi a écrit : > On Thu, Nov 30, 2017 at 12:43:20PM +0530, Kishon Vijay Abraham I wrote: > > [...] > >>>> For linux-next, I applied this series on top of Kishon's patch >>>> ("PCI: endpoint: Use EPC's device in dma_alloc_coherent/dma_free_coherent") >>>> otherwise dma_alloc_coherent() fails when called by pci_epf_alloc_space(). >>>> >>>> Also, I patched drivers/Makefile rather than drivers/pci/Makefile to make >>>> the drivers/pci/cadence/pcie-cadence-ep.o linked after >> >> The reason to patch drivers/Makefile should be because pcie-cadence-ep has to >> be compiled even when CONFIG_PCI is not enabled. CONFIG_PCI enables host >> specific features and ENDPOINT shouldn't depend on CONFIG_PCI. >>>> drivers/pci/endpoint/*.o objects, otherwise the built-in pci-cadence-ep >>>> driver would be probed before the PCI endpoint framework would have been >>>> initialized, which results in a kernel crash. >>> >>> Nice :( - isn't there a way to improve this (ie probe deferral or >>> registering the EPF bus earlier) ? >>> >>>> I guess this is the reason why the "pci/dwc" line was also put in >>>> drivers/Makefile, right after the "pci/endpoint" line. >>> >>> Or probably the other way around - see commit 5e8cb4033807 >>> >>> @Kishon, thoughts ? >> >> Lorenzo, ordering Makefile is one way to initialize EP core before > > Makefile ordering is fragile, I do not like relying on it. > >> other drivers. the other way is to have PCI EP core have a different >> initcall level.. subsys_initcall?? > > Yes, registering the bus at eg postcore_initcall() as PCI does should do > (if that's the problem this is solving) but still, the code must not > crash if the ordering is not correct, we have to fix this regardless. > > I would appreciate if Cyrille can debug the cause of the kernel crash > so that we can fix it in the longer term. > I had the crash kernel few weeks ago hence I have to test again to confirm but if I remember correctly it was a NULL pointer dereferencing crash: cdns_pcie_ep_probe() | +--> devm_pci_epc_create() | +--> __devm_pci_ep_create() | +--> __pci_epc_create() | +--> pci_ep_cfs_add_epc_group() | | /* | * Here controllers_group is still NULL because | * pci_ep_cfs_init() has not been called yet. | */ +--> configfs_register_group(controllers_group, ...) | +--> link_group() /* Dereferencing NULL pointer */ Best regards, Cyrille > Thanks, > Lorenzo > -- Cyrille Pitchen, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com