On Thu, Jul 4, 2019 at 1:20 AM Joerg Roedel <joro@xxxxxxxxxx> wrote: > > 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. correct > > + /* > > + * 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. At least for the OF case, it happens in the of_dma_configure() which happens from really_probe(), so there is normally a driver. There are a few exceptional cases, where drivers call of_dma_configure() on their own sub-device without a driver attached (hence the need to check if dev->driver is NULL). I'm also interested in the ACPI case eventually... the aarch64 "windows" laptops do have ACPI. But for now we are booting with DT since there is quite a lot of work before we get to point of using ACPI. (In particular, under windows, device power management is done thru a Platform Extension Plugin (PEP), but so far linux has no such mechanism.) We really don't have control of the firmware. But when arm-smmu is probed it can read back the hw state and figure out what is going on (with an RFC series[1] from Bjorn which was posted earlier), so we don't really need to depend on the firmware. > > - 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? It is set in the driver in the second patch[2] in this series. BR, -R [1] https://www.spinics.net/lists/arm-kernel/msg732246.html [2] https://patchwork.freedesktop.org/patch/315291/
