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[ Upstream commit6d2e369f0d] The NVIDIA Turing GPU is a multi-function PCI device with the following functions: - Function 0: VGA display controller - Function 1: Audio controller - Function 2: USB xHCI Host controller - Function 3: USB Type-C UCSI controller Function 0 is tightly coupled with other functions in the hardware. When function 0 is in D3, it gates power for hardware blocks used by other functions, which means those functions only work when function 0 is in D0. If any of these functions (1/2/3) are in D0, then function 0 should also be in D0. Commit07f4f97d7b("vga_switcheroo: Use device link for HDA controller") already creates a device link to show the dependency of function 1 on function 0 of this GPU. Create additional device links to express the dependencies of functions 2 and 3 on function 0. This means function 0 will be in D0 if any other function is in D0. [bhelgaas: I think the PCI spec expectation is that functions can be power-managed independently, so I don't think this device is technically compliant. For example, the PCIe r5.0 spec, sec 1.4, says "the PCI/PCIe hardware/software model includes architectural constructs necessary to discover, configure, and use a Function, without needing Function-specific knowledge" and sec 5.1 says "D states are associated with a particular Function" and "PM provides ... a mechanism to identify power management capabilities of a given Function [and] the ability to transition a Function into a certain power management state."] Link: https://lore.kernel.org/lkml/20190606092225.17960-3-abhsahu@nvidia.com Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com> [bhelgaas: commit log] Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.