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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@nvidia.com> Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> Link: https://lore.kernel.org/r/20250708-nova-docs-v4-6-9d188772c4c7@nvidia.com Signed-off-by: Danilo Krummrich <dakr@kernel.org>
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.. SPDX-License-Identifier: GPL-2.0
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==================================
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Device Initialization (devinit)
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==================================
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The devinit process is complex and subject to change. This document provides a high-level
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overview using the Ampere GPU family as an example. The goal is to provide a conceptual
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overview of the process to aid in understanding the corresponding kernel code.
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Device initialization (devinit) is a crucial sequence of register read/write operations
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that occur after a GPU reset. The devinit sequence is essential for properly configuring
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the GPU hardware before it can be used.
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The devinit engine is an interpreter program that typically runs on the PMU (Power Management
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Unit) microcontroller of the GPU. This interpreter executes a "script" of initialization
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commands. The devinit engine itself is part of the VBIOS ROM in the same ROM image as the
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FWSEC (Firmware Security) image (see fwsec.rst and vbios.rst) and it runs before the
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nova-core driver is even loaded. On an Ampere GPU, the devinit ucode is separate from the
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FWSEC ucode. It is launched by FWSEC, which runs on the GSP in 'heavy-secure' mode, while
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devinit runs on the PMU in 'light-secure' mode.
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Key Functions of devinit
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------------------------
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devinit performs several critical tasks:
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1. Programming VRAM memory controller timings
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2. Power sequencing
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3. Clock and PLL (Phase-Locked Loop) configuration
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4. Thermal management
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Low-level Firmware Initialization Flow
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--------------------------------------
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Upon reset, several microcontrollers on the GPU (such as PMU, SEC2, GSP, etc.) run GPU
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firmware (gfw) code to set up the GPU and its core parameters. Most of the GPU is
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considered unusable until this initialization process completes.
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These low-level GPU firmware components are typically:
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1. Located in the VBIOS ROM in the same ROM partition (see vbios.rst and fwsec.rst).
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2. Executed in sequence on different microcontrollers:
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- The devinit engine typically but not necessarily runs on the PMU.
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- On an Ampere GPU, the FWSEC typically runs on the GSP (GPU System Processor) in
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heavy-secure mode.
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Before the driver can proceed with further initialization, it must wait for a signal
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indicating that core initialization is complete (known as GFW_BOOT). This signal is
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asserted by the FWSEC running on the GSP in heavy-secure mode.
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Runtime Considerations
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----------------------
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It's important to note that the devinit sequence also needs to run during suspend/resume
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operations at runtime, not just during initial boot, as it is critical to power management.
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Security and Access Control
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---------------------------
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The initialization process involves careful privilege management. For example, before
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accessing certain completion status registers, the driver must check privilege level
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masks. Some registers are only accessible after secure firmware (FWSEC) lowers the
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privilege level to allow CPU (LS/low-secure) access. This is the case, for example,
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when receiving the GFW_BOOT signal. |