The secure firmware keeps some SID override registers set as passthrough
in order to allow devices such as the display controller to operate with
no knowledge of SMMU translations until an operating system driver takes
over. This is needed in order to seamlessly transition from the firmware
framebuffer to the OS framebuffer.

Upon successfully attaching a device to the SMMU and in the process
creating identity mappings for memory regions that are being accessed,
the Tegra implementation will call into the memory controller driver to
program the override SIDs appropriately.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20210603164632.1000458-6-thierry.reding@gmail.comSigned-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>