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IMS (Interrupt Message Store) is a new specification which allows
implementation specific storage of MSI messages contrary to the
strict standard specified MSI and MSI-X message stores.
This requires new device specific interrupt domains to handle the
implementation defined storage which can be an array in device memory or
host/guest memory which is shared with hardware queues.
Add a function to create IMS domains for PCI devices. IMS domains are using
the new per device domain mechanism and are configured by the device driver
via a template. IMS domains are created as secondary device domains so they
work side on side with MSI[-X] on the same device.
The IMS domains have a few constraints:
- The index space is managed by the core code.
Device memory based IMS provides a storage array with a fixed size
which obviously requires an index. But there is no association between
index and functionality so the core can randomly allocate an index in
the array.
System memory based IMS does not have the concept of an index as the
storage is somewhere in memory. In that case the index is purely
software based to keep track of the allocations.
- There is no requirement for consecutive index ranges
This is currently a limitation of the MSI core and can be implemented
if there is a justified use case by changing the internal storage from
xarray to maple_tree. For now it's single vector allocation.
- The interrupt chip must provide the following callbacks:
- irq_mask()
- irq_unmask()
- irq_write_msi_msg()
- The interrupt chip must provide the following optional callbacks
when the irq_mask(), irq_unmask() and irq_write_msi_msg() callbacks
cannot operate directly on hardware, e.g. in the case that the
interrupt message store is in queue memory:
- irq_bus_lock()
- irq_bus_unlock()
These callbacks are invoked from preemptible task context and are
allowed to sleep. In this case the mandatory callbacks above just
store the information. The irq_bus_unlock() callback is supposed to
make the change effective before returning.
- Interrupt affinity setting is handled by the underlying parent
interrupt domain and communicated to the IMS domain via
irq_write_msi_msg(). IMS domains cannot have a irq_set_affinity()
callback. That's a reasonable restriction similar to the PCI/MSI
device domain implementations.
The domain is automatically destroyed when the PCI device is removed.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221124232326.904316841@linutronix.de
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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.