From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758115Ab3LWViv (ORCPT ); Mon, 23 Dec 2013 16:38:51 -0500 Received: from smtp4.epfl.ch ([128.178.224.219]:52662 "EHLO smtp4.epfl.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757911Ab3LWVhI (ORCPT ); Mon, 23 Dec 2013 16:37:08 -0500 Message-ID: <52B8A5F8.3000706@epfl.ch> Date: Mon, 23 Dec 2013 22:07:04 +0100 From: Florian Vaussard Reply-To: florian.vaussard@epfl.ch User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: "Anna, Suman" , Joerg Roedel , Tony Lindgren , =?ISO-8859-1?Q?Beno=EEt_Cousson?= CC: Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Rob Landley , Grant Likely , Hiroshi Doyu , "iommu@lists.linux-foundation.org" , "devicetree@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-omap@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 1/7] iommu/omap: Do bus_set_iommu() only if probe() succeeds References: <1387284818-28739-1-git-send-email-florian.vaussard@epfl.ch> <1387284818-28739-2-git-send-email-florian.vaussard@epfl.ch> <52B888C2.8040303@ti.com> In-Reply-To: <52B888C2.8040303@ti.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Suman, On 12/23/2013 08:02 PM, Anna, Suman wrote: > Hi Florian, > > On 12/17/2013 06:53 AM, Florian Vaussard wrote: >> Currently, bus_set_iommu() is done in omap_iommu_init(). However, >> omap_iommu_probe() can fail in a number of ways, leaving the platform >> bus with a dangling reference to a non-initialized iommu. Perform >> bus_set_iommu() only if omap_iommu_probe() succeed. > > Can you clarify a bit more on what kind of issues you were seeing > specifically? In general, there can be multiple instances of the iommu, > so setting it in probe may not be fixing whatever issue you were seeing. > The current OMAP3 code has only the ISP MMU enabled, but there is also > another one for the IVA MMU (currently not configured by default). > Moving the bus_set_iommu to probe makes sense if only one iommu is > present, so this patch may not be needed at all. > If omap_iommu_probe() fails, the init will have called bus_set_iommu() anyways. Thus, when a driver request the iommu by calling iommu_domain_alloc(), it will succeed (but iommu_attach_device() will fail if I remember). Leaving a driver with a dangling reference to a phantom iommu is not good IMHO. It will lead to strange behaviours one day or another. As for the multiple iommu case, as I do not think it is currently possible, as bus_type (in this case &platform_bus_type) has only one struct iommu_ops. bus_set_iommu() will return EBUSY on the second call. Am I missing something? > Also, the main change in this patch is moving the bus_set_iommu from > omap_iommu_init to omap_iommu_probe, so you should probably leave out > moving the function. The omap_iommu_probe function would anyway need > conversion to using devm_ functions. > This was my first try also, but as bus_set_iommu() needs omap_iommu_ops (itself depending on several functions), its call must come after the declaration of omap_iommu_ops. Thus I moved omap_iommu_probe() after the declaration of omap_iommu_ops. But I can probably use a forward declaration for omap_iommu_ops, this would be better. Indeed, we can also convert to devm_. Regards, Florian