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According to [PCIe v5 9.6.2] for PF Device Power Management States "The PF's power management state (D-state) has global impact on its associated VFs. If a VF does not implement the Power Management Capability, then it behaves as if it is in an equivalent power state of its associated PF. If a VF implements the Power Management Capability, the Device behavior is undefined if the PF is placed in a lower power state than the VF. Software should avoid this situation by placing all VFs in lower power state before lowering their associated PF's power state." From the vfio driver side, user can enable SR-IOV when the PF is in D3hot state. If VF does not implement the Power Management Capability, then the VF will be actually in D3hot state and then the VF BAR access will fail. If VF implements the Power Management Capability, then VF will assume that its current power state is D0 when the PF is D3hot and in this case, the behavior is undefined. To support PF power management, we need to create power management dependency between PF and its VF's. The runtime power management support may help with this where power management dependencies are supported through device links. But till we have such support in place, we can disallow the PF to go into low power state, if PF has VF enabled. There can be a case, where user first enables the VF's and then disables the VF's. If there is no user of PF, then the PF can put into D3hot state again. But with this patch, the PF will still be in D0 state after disabling VF's since detecting this case inside vfio_pci_core_sriov_configure() requires access to struct vfio_device::open_count along with its locks. But the subsequent patches related to runtime PM will handle this case since runtime PM maintains its own usage count. Also, vfio_pci_core_sriov_configure() can be called at any time (with and without vfio pci device user), so the power state change and SR-IOV enablement need to be protected with the required locks. Signed-off-by: Abhishek Sahu <abhsahu@nvidia.com> Link: https://lore.kernel.org/r/20220518111612.16985-3-abhsahu@nvidia.com Signed-off-by: Alex Williamson <alex.williamson@redhat.com> |
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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.