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Message-ID: <20250503040802.1411285-6-joelagnelf@nvidia.com>
Date: Sat, 3 May 2025 00:07:57 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: linux-kernel@...r.kernel.org,
Danilo Krummrich <dakr@...nel.org>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>,
Simona Vetter <simona@...ll.ch>,
Jonathan Corbet <corbet@....net>
Cc: nouveau@...ts.freedesktop.org,
dri-devel@...ts.freedesktop.org,
Alexandre Courbot <acourbot@...dia.com>,
John Hubbard <jhubbard@...dia.com>,
Shirish Baskaran <sbaskaran@...dia.com>,
Alistair Popple <apopple@...dia.com>,
Timur Tabi <ttabi@...dia.com>,
Ben Skeggs <bskeggs@...dia.com>,
rust-for-linux@...r.kernel.org,
Joel Fernandes <joelagnelf@...dia.com>,
linux-doc@...r.kernel.org
Subject: [PATCH v2 5/7] docs: nova-core: Document devinit process
devinit is mentioned in the code. This patch explains it so it is clear
what it does. devinit is not only essential at boot-time, but also at
runtime due to suspend-resume and things like re-clocking.
Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
---
Documentation/gpu/nova/core/devinit.rst | 59 +++++++++++++++++++++++++
Documentation/gpu/nova/index.rst | 1 +
drivers/gpu/nova-core/devinit.rs | 6 +--
3 files changed, 63 insertions(+), 3 deletions(-)
create mode 100644 Documentation/gpu/nova/core/devinit.rst
diff --git a/Documentation/gpu/nova/core/devinit.rst b/Documentation/gpu/nova/core/devinit.rst
new file mode 100644
index 000000000000..85e7033dd3a7
--- /dev/null
+++ b/Documentation/gpu/nova/core/devinit.rst
@@ -0,0 +1,59 @@
+.. SPDX-License-Identifier: GPL-2.0
+==================================
+Device Initialization (devinit)
+==================================
+Note that devinit itself is a complicated process, subject to change, and this document
+only roughly provides an overview of the process using the Ampere GPU family as an example.
+The idea is to provide a conceptual overview of the process to help understand the kernel
+code that deals with it.
+
+Device initialization (devinit) is a crucial sequence of register read/write operations
+that occur after a GPU reset. The devinit sequence is essential for properly configuring
+the GPU hardware before it can be used.
+
+The devinit engine is an interpreter program that typically runs on the PMU (Power Management
+Unit) microcontroller of the GPU. This interpreter executes a "script" of initialization
+commands. The devinit engine itself is part of the VBIOS ROM in the same ROM image as the
+FWSEC (Firmware Security) image (see fwsec.rst and vbios.rst) and it runs before the
+nova-core driver is even loaded. On an Ampere GPU, the devinit ucode (which is separate
+from the FWSEC ucode), is launched by the FWSEC (FWSEC runs on GSP in heavy-secure mode
+and devinit runs on PMU in light-secure mode).
+
+Key Functions of devinit
+------------------------
+devinit performs several critical tasks:
+
+1. Programming VRAM memory controller timings
+2. Power sequencing
+3. Clock and PLL (Phase-Locked Loop) configuration
+4. Thermal management
+
+Low-level Firmware Initialization Flow
+--------------------------------------
+Upon reset, several microcontrollers on the GPU (such as PMU, SEC2, GSP, etc.) run GPU
+firmware (gfw) code to set up the GPU and its core parameters. Most of the GPU is
+considered unusable until this initialization process completes.
+
+These low-level GPU firmware components are typically:
+1. Located in the VBIOS ROM in the same ROM partition (see vbios.rst and fwsec.rst).
+2. Executed in sequence on different microcontrollers:
+ - The devinit engine typically but not necessarily runs on the PMU.
+ - On an Ampere GPU, the FWSEC typically runs on the GSP (GPU System Processor) in
+ heavy-secure mode.
+
+Before the driver can proceed with further initialization, it must wait for a signal
+indicating that core initialization is complete (known as GFW_BOOT). This signal is
+asserted by the FWSEC running on the GSP in heavy-secure mode.
+
+Runtime Considerations
+---------------------
+It's important to note that the devinit sequence also needs to run during suspend/resume
+operations at runtime, not just during initial boot, as it is critical to power management.
+
+Security and Access Control
+--------------------------
+The initialization process involves careful privilege management. For example, before
+accessing certain completion status registers, the driver must check privilege level
+masks. Some registers are only accessible after secure firmware (FWSEC) lowers the
+privilege level to allow CPU (LS/low-secure) access. For example, to receive the
+GFW_BOOT signal.
\ No newline at end of file
diff --git a/Documentation/gpu/nova/index.rst b/Documentation/gpu/nova/index.rst
index 22e5712ac6b0..301435c5cf67 100644
--- a/Documentation/gpu/nova/index.rst
+++ b/Documentation/gpu/nova/index.rst
@@ -29,4 +29,5 @@ vGPU manager VFIO driver and the nova-drm driver.
core/guidelines
core/vbios
core/fwsec
+ core/devinit
core/todo
diff --git a/drivers/gpu/nova-core/devinit.rs b/drivers/gpu/nova-core/devinit.rs
index 21fc9b96d498..bd6a5c57c444 100644
--- a/drivers/gpu/nova-core/devinit.rs
+++ b/drivers/gpu/nova-core/devinit.rs
@@ -10,8 +10,8 @@
//! 3. Clock and PLL configuration.
//! 4. Thermal management.
//!
-//! devinit itself is a 'script' which is interpreted by the PMU microcontroller of
-//! the GPU by an interpreter program.
+//! devinit itself is a 'script' which is interpreted by a microcontroller of
+//! the GPU by an interpreter program (typically running on the PMU).
//!
//! Note that the devinit sequence also needs to run during suspend/resume at runtime.
@@ -30,7 +30,7 @@
///
/// The GPU firmware (gfw) code includes several components that execute before the driver loads.
/// These components are located in the VBIOS ROM and are executed in a sequence on these different
-/// microcontrollers. The devinit sequence itself runs on the PMU, and the FWSEC runs on the GSP.
+/// microcontrollers. The devinit sequence typically runs on the PMU, and the FWSEC runs on the GSP.
///
/// This function specifically waits for a signal indicating core initialization is complete before
/// which not much can be done. This signal is setup by the FWSEC running on the GSP in Heavy-secured
--
2.43.0
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