Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751533AbdISKrF (ORCPT ); Tue, 19 Sep 2017 06:47:05 -0400 Received: from foss.arm.com ([217.140.101.70]:48452 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751284AbdISKrD (ORCPT ); Tue, 19 Sep 2017 06:47:03 -0400 Subject: Re: [PATCH] iommu/ipmmu-vmsa: Do not replace bus IOMMU ops on driver init. To: Laurent Pinchart , Liviu Dudau Cc: Laurent Pinchart , Geert Uytterhoeven , Shawn Lin , Magnus Damm , LKML , IOMMU ML References: <20170918100444.21878-1-Liviu.Dudau@arm.com> <2550948.Yqn2DEl6fn@avalon> From: Robin Murphy Message-ID: <944ded5f-58b9-43a9-fe1d-191b982545fa@arm.com> Date: Tue, 19 Sep 2017 11:47:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <2550948.Yqn2DEl6fn@avalon> Content-Type: text/plain; charset=utf-8 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: 3336 Lines: 91 Hi Laurent, On 19/09/17 08:07, Laurent Pinchart wrote: > Hi Liviu, > > Thank you for the patch. > > On Monday, 18 September 2017 13:04:44 EEST Liviu Dudau wrote: >> If the IPMMU driver is compiled in the kernel it will replace the >> platform bus IOMMU ops on running the ipmmu_init() function, regardless >> if there is any IPMMU hardware present or not. This screws up systems >> that just want to build a generic kernel that runs on multiple platforms >> and use a different IOMMU implementation. >> >> Move the bus_set_iommu() call at the end of the ipmmu_probe() function >> when we know that hardware is present. With current IOMMU framework it >> should be safe (at least for OF case). > > If I recall correctly the issue is that the IPMMU might be probed after bus > master devices when using the legacy IOMMU DT integration, which the ipmmu- > vmsa driver does on ARM32. Calling bus_set_iommu() from the probe function > will then result in some devices losing IOMMU support. Yes, that used to be the problem, but since IPMMU uses the generic bindings and iommu_device_register(), it should now benefit from client probe-deferral even when it doesn't support of_xlate(). Robin. >> Now that the ipmmu_init() and ipmmu_exit() functions are simple calls to >> platform_driver_register() and platform_driver_unregister(), replace >> them with the module_platform_driver() macro call. >> >> Signed-off-by: Liviu Dudau >> Cc: Laurent Pinchart >> --- >> drivers/iommu/ipmmu-vmsa.c | 29 +++++------------------------ >> 1 file changed, 5 insertions(+), 24 deletions(-) >> >> diff --git a/drivers/iommu/ipmmu-vmsa.c b/drivers/iommu/ipmmu-vmsa.c >> index 2a38aa15be17d..c60569c74678d 100644 >> --- a/drivers/iommu/ipmmu-vmsa.c >> +++ b/drivers/iommu/ipmmu-vmsa.c >> @@ -1055,10 +1055,11 @@ static int ipmmu_probe(struct platform_device *pdev) >> ipmmu_device_reset(mmu); >> >> /* >> - * We can't create the ARM mapping here as it requires the bus to have >> - * an IOMMU, which only happens when bus_set_iommu() is called in >> - * ipmmu_init() after the probe function returns. >> + * Now that we have validated the presence of the hardware, set >> + * the bus IOMMU ops to enable future domain and device setup. >> */ >> + if (!iommu_present(&platform_bus_type)) >> + bus_set_iommu(&platform_bus_type, &ipmmu_ops); >> >> spin_lock(&ipmmu_devices_lock); >> list_add(&mmu->list, &ipmmu_devices); > > What branch is this patch based on ? ipmmu_devices_lock isn't in mainline. > >> @@ -1100,27 +1101,7 @@ static struct platform_driver ipmmu_driver = { >> .remove = ipmmu_remove, >> }; >> >> -static int __init ipmmu_init(void) >> -{ >> - int ret; >> - >> - ret = platform_driver_register(&ipmmu_driver); >> - if (ret < 0) >> - return ret; >> - >> - if (!iommu_present(&platform_bus_type)) >> - bus_set_iommu(&platform_bus_type, &ipmmu_ops); >> - >> - return 0; >> -} >> - >> -static void __exit ipmmu_exit(void) >> -{ >> - return platform_driver_unregister(&ipmmu_driver); >> -} >> - >> -subsys_initcall(ipmmu_init); >> -module_exit(ipmmu_exit); >> +module_platform_driver(ipmmu_driver); >> >> MODULE_DESCRIPTION("IOMMU API for Renesas VMSA-compatible IPMMU"); >> MODULE_AUTHOR("Laurent Pinchart "); >