From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH 1/2] iommu: add support for drivers that manage iommu explicitly Date: Thu, 4 Jul 2019 10:20:01 +0200 Message-ID: <20190704082001.GD6546@8bytes.org> References: <20190702202631.32148-1-robdclark@gmail.com> <20190702202631.32148-2-robdclark@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190702202631.32148-2-robdclark@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Rob Clark Cc: iommu@lists.linux-foundation.org, dri-devel@lists.freedesktop.org, aarch64-laptops@lists.linaro.org, Jordan Crouse , Rob Clark , Greg Kroah-Hartman , "Rafael J. Wysocki" , Ulf Hansson , Rasmus Villemoes , Heikki Krogerus , Vivek Gautam , Bartosz Golaszewski , Joe Perches , Sudeep Holla , linux-kernel@vger.kernel.org List-Id: dri-devel@lists.freedesktop.org Hi Rob, On Tue, Jul 02, 2019 at 01:26:18PM -0700, Rob Clark wrote: > 1) In some cases the bootloader takes the iommu out of bypass and > enables the display. This is in particular a problem on the aarch64 > laptops that exist these days, and modern snapdragon android devices. > (Older devices also enabled the display in bootloader but did not > take the iommu out of bypass.) Attaching a DMA or IDENTITY domain > while scanout is active, before the driver has a chance to intervene, > makes things go *boom* Just to make sure I get this right: The bootloader inializes the SMMU and creates non-identity mappings for the GPU? And when the SMMU driver in Linux takes over this breaks display output. > + /* > + * If driver is going to manage iommu directly, then avoid > + * attaching any non driver managed domain. There could > + * be already active dma underway (ie. scanout in case of > + * bootloader enabled display), and interfering with that > + * will make things go *boom* > + */ > + if ((domain->type != IOMMU_DOMAIN_UNMANAGED) && > + dev->driver && dev->driver->driver_manages_iommu) > + return 0; > + When the default domain is attached, there is usually no driver attached yet. I think this needs to be communicated by the firmware to Linux and the code should check against that. > - bool suppress_bind_attrs; /* disables bind/unbind via sysfs */ > + bool suppress_bind_attrs:1; /* disables bind/unbind via sysfs */ > + bool driver_manages_iommu:1; /* driver manages IOMMU explicitly */ How does this field get set? Joerg