Re: [PATCH v2 0/5] iommu: Support identity mappings of reserved-memory regions

23.04.2021 19:32, Thierry Reding пишет:

Hi,

this is an updated proposal to solve the problem of passing memory
regions that are actively being accessed during boot. The particular
use-case that I need this for is when the bootloader has set up the
display controller to scan out a boot splash screen. During boot the
DMA/IOMMU glue code will attach devices to an IOMMU domain and by
doing so enable IOMMU translations. Typically this will be before a
device driver has had a chance to either disable the display
controller or set up a new framebuffer and map it to the IOMMU.

Hello Thierry,

Is it always safe to enable SMMU ASID in a middle of a DMA request made
by a memory client?

The memory controller supports blocking DMA requests, which we are
already using for the memory hot-resetting. A block could be needed
before ASID is toggled. This needs to be clarified.