linux-stable-mirror/Documentation/gpu/amdgpu/driver-core.rst

============================
 Core Driver Infrastructure
============================

GPU Hardware Structure
======================

Each ASIC is a collection of hardware blocks.  We refer to them as
"IPs" (Intellectual Property blocks).  Each IP encapsulates certain
functionality. IPs are versioned and can also be mixed and matched.
E.g., you might have two different ASICs that both have System DMA (SDMA) 5.x IPs.
The driver is arranged by IPs.  There are driver components to handle
the initialization and operation of each IP.  There are also a bunch
of smaller IPs that don't really need much if any driver interaction.
Those end up getting lumped into the common stuff in the soc files.
The soc files (e.g., vi.c, soc15.c nv.c) contain code for aspects of
the SoC itself rather than specific IPs.  E.g., things like GPU resets
and register access functions are SoC dependent.

An APU contains more than just CPU and GPU, it also contains all of
the platform stuff (audio, usb, gpio, etc.).  Also, a lot of
components are shared between the CPU, platform, and the GPU (e.g.,
SMU, PSP, etc.).  Specific components (CPU, GPU, etc.) usually have
their interface to interact with those common components.  For things
like S0i3 there is a ton of coordination required across all the
components, but that is probably a bit beyond the scope of this
section.

With respect to the GPU, we have the following major IPs:

GMC (Graphics Memory Controller)
    This was a dedicated IP on older pre-vega chips, but has since
    become somewhat decentralized on vega and newer chips.  They now
    have dedicated memory hubs for specific IPs or groups of IPs.  We
    still treat it as a single component in the driver however since
    the programming model is still pretty similar.  This is how the
    different IPs on the GPU get the memory (VRAM or system memory).
    It also provides the support for per process GPU virtual address
    spaces.

IH (Interrupt Handler)
    This is the interrupt controller on the GPU.  All of the IPs feed
    their interrupts into this IP and it aggregates them into a set of
    ring buffers that the driver can parse to handle interrupts from
    different IPs.

PSP (Platform Security Processor)
    This handles security policy for the SoC and executes trusted
    applications, and validates and loads firmwares for other blocks.

SMU (System Management Unit)
    This is the power management microcontroller.  It manages the entire
    SoC.  The driver interacts with it to control power management
    features like clocks, voltages, power rails, etc.

DCN (Display Controller Next)
    This is the display controller.  It handles the display hardware.
    It is described in more details in :ref:`Display Core <amdgpu-display-core>`.

SDMA (System DMA)
    This is a multi-purpose DMA engine.  The kernel driver uses it for
    various things including paging and GPU page table updates.  It's also
    exposed to userspace for use by user mode drivers (OpenGL, Vulkan,
    etc.)

GC (Graphics and Compute)
    This is the graphics and compute engine, i.e., the block that
    encompasses the 3D pipeline and shader blocks.  This is by far the
    largest block on the GPU.  The 3D pipeline has tons of sub-blocks.  In
    addition to that, it also contains the CP microcontrollers (ME, PFP, CE,
    MEC) and the RLC microcontroller.  It's exposed to userspace for user mode
    drivers (OpenGL, Vulkan, OpenCL, etc.). More details in :ref:`Graphics (GFX)
    and Compute <amdgpu-gc>`.

VCN (Video Core Next)
    This is the multi-media engine.  It handles video and image encode and
    decode.  It's exposed to userspace for user mode drivers (VA-API,
    OpenMAX, etc.)

It is important to note that these blocks can interact with each other. The
picture below illustrates some of the components and their interconnection:

.. kernel-figure:: amd_overview_block.svg

In the diagram, memory-related blocks are shown in green. Notice that specific
IPs have a green square that represents a small hardware block named 'hub',
which is responsible for interfacing with memory. All memory hubs are connected
in the UMCs, which in turn are connected to memory blocks. As a note,
pre-vega devices have a dedicated block for the Graphic Memory Controller
(GMC), which was replaced by UMC and hubs in new architectures. In the driver
code, you can identify this component by looking for the suffix hub, for
example: gfxhub, dchub, mmhub, vmhub, etc. Keep in mind that the component's
interaction with the memory block may vary across architectures. For example,
on Navi and newer, GC and SDMA are both attached to GCHUB; on pre-Navi, SDMA
goes through MMHUB; VCN, JPEG, and VPE go through MMHUB; DCN goes through
DCHUB.

There is some protection for certain memory elements, and the PSP plays an
essential role in this area. When a specific firmware is loaded into memory,
the PSP takes steps to ensure it has a valid signature. It also stores firmware
images in a protected memory area named Trusted Memory Area (TMR), so the OS or
driver can't corrupt them at runtime. Another use of PSP is to support Trusted
Applications (TA), which are basically small applications that run on the
trusted processor and handles a trusted operation (e.g., HDCP). PSP is also
used for encrypted memory for content protection via Trusted Memory Zone (TMZ).

Another critical IP is the SMU. It handles reset distribution, as well as
clock, thermal, and power management for all IPs on the SoC. SMU also helps to
balance performance and power consumption.

.. _pipes-and-queues-description:

GFX, Compute, and SDMA Overall Behavior
=======================================

.. note:: For simplicity, whenever the term block is used in this section, it
   means GFX, Compute, and SDMA.

GFX, Compute and SDMA share a similar form of operation that can be abstracted
to facilitate understanding of the behavior of these blocks. See the figure
below illustrating the common components of these blocks:

.. kernel-figure:: pipe_and_queue_abstraction.svg

In the central part of this figure, you can see two hardware elements, one called
**Pipes** and another called **Queues**; it is important to highlight that Queues
must be associated with a Pipe and vice-versa. Every specific hardware IP may have
a different number of Pipes and, in turn, a different number of Queues; for
example, GFX 11 has two Pipes and two Queues per Pipe for the GFX front end.

Pipe is the hardware that processes the instructions available in the Queues;
in other words, it is a thread executing the operations inserted in the Queue.
One crucial characteristic of Pipes is that they can only execute one Queue at
a time; no matter if the hardware has multiple Queues in the Pipe, it only runs
one Queue per Pipe.

Pipes have the mechanics of swapping between queues at the hardware level.
Nonetheless, they only make use of Queues that are considered mapped. Pipes can
switch between queues based on any of the following inputs:

1. Command Stream;
2. Packet by Packet;
3. Other hardware requests the change (e.g., MES).

Queues within Pipes are defined by the Hardware Queue Descriptors (HQD).
Associated with the HQD concept, we have the Memory Queue Descriptor (MQD),
which is responsible for storing information about the state of each of the
available Queues in the memory. The state of a Queue contains information such
as the GPU virtual address of the queue itself, save areas, doorbell, etc. The
MQD also stores the HQD registers, which are vital for activating or
deactivating a given Queue.  The scheduling firmware (e.g., MES) is responsible
for loading HQDs from MQDs and vice versa.

The Queue-switching process can also happen with the firmware requesting the
preemption or unmapping of a Queue. The firmware waits for the HQD_ACTIVE bit
to change to low before saving the state into the MQD. To make a different
Queue become active, the firmware copies the MQD state into the HQD registers
and loads any additional state. Finally, it sets the HQD_ACTIVE bit to high to
indicate that the queue is active.  The Pipe will then execute work from active
Queues.

Driver Structure
================

In general, the driver has a list of all of the IPs on a particular
SoC and for things like init/fini/suspend/resume, more or less just
walks the list and handles each IP.

Some useful constructs:

KIQ (Kernel Interface Queue)
    This is a control queue used by the kernel driver to manage other gfx
    and compute queues on the GFX/compute engine.  You can use it to
    map/unmap additional queues, etc.  This is replaced by MES on
    GFX 11 and newer hardware.

IB (Indirect Buffer)
    A command buffer for a particular engine.  Rather than writing
    commands directly to the queue, you can write the commands into a
    piece of memory and then put a pointer to the memory into the queue.
    The hardware will then follow the pointer and execute the commands in
    the memory, then returning to the rest of the commands in the ring.

.. _amdgpu_memory_domains:

Memory Domains
==============

.. kernel-doc:: include/uapi/drm/amdgpu_drm.h
   :doc: memory domains

Buffer Objects
==============

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
   :doc: amdgpu_object

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
   :internal:

PRIME Buffer Sharing
====================

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
   :doc: PRIME Buffer Sharing

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
   :internal:

MMU Notifier
============

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c
   :doc: MMU Notifier

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c
   :internal:

AMDGPU Virtual Memory
=====================

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
   :doc: GPUVM

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
   :internal:

Interrupt Handling
==================

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_irq.c
   :doc: Interrupt Handling

.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_irq.c
   :internal:

IP Blocks
=========

.. kernel-doc:: drivers/gpu/drm/amd/include/amd_shared.h
   :doc: IP Blocks

.. kernel-doc:: drivers/gpu/drm/amd/include/amd_shared.h
   :identifiers: amd_ip_block_type amd_ip_funcs DC_FEATURE_MASK DC_DEBUG_MASK