d5237c7c9b
On Tegra194, all clients of the memory subsystem can generally address
40 bits of system memory. However, bit 39 has special meaning and will
cause the memory controller to reorder sectors for block-linear buffer
formats. This is primarily useful for graphics-related devices.
Use of bit 39 must be controlled on a case-by-case basis. Buffers that
are used with bit 39 set by one device may be used with bit 39 cleared
by other devices.
Care must be taken to allocate buffers at addresses that do not require
bit 39 to be set. This is normally not an issue for system memory since
there are no Tegra-based systems with enough RAM to exhaust the 39-bit
physical address space. However, when a device is behind an IOMMU, such
as the ARM SMMU on Tegra194, the IOMMUs input address space can cause
IOVA allocations to happen in this region. This is for example the case
when an operating system implements a top-down allocation policy for IO
virtual addresses.
To account for this, describe the path that memory accesses take through
the system. Memory clients will send requests to the memory controller,
which forwards bits [38:0] of the address either to the external memory
controller or the SMMU, depending on the stream ID of the access. A good
way to describe this is using the interconnects bindings, see:
Documentation/devicetree/bindings/interconnect/interconnect.txt
The standard "dma-mem" path is used to describe the path towards system
memory via the memory controller. A dma-ranges property in the memory
controller's device tree node limits the range of DMA addresses that the
memory clients can use to bits [38:0], ensuring that bit 39 is not used.
Signed-off-by: Thierry Reding <treding@nvidia.com>
---
Changes in v4:
- add additional entries for interconnect-names to match interconnects
- add EMC as destination for interconnect paths
Changes in v3:
- add missing interconnect properties for VIC
Changes in v2:
- use memory client IDs instead of stream IDs (Mikko Perttunen)
Signed-off-by: Thierry Reding <treding@nvidia.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.