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Add MSI doorbell support to reduce latency between PCI host and EP. Before this change: ping 169.254.172.137 64 bytes from 169.254.172.137: icmp_seq=1 ttl=64 time=0.575 ms 64 bytes from 169.254.172.137: icmp_seq=2 ttl=64 time=1.80 ms 64 bytes from 169.254.172.137: icmp_seq=3 ttl=64 time=8.19 ms 64 bytes from 169.254.172.137: icmp_seq=4 ttl=64 time=2.00 ms After this change: ping 169.254.144.71 64 bytes from 169.254.144.71: icmp_seq=1 ttl=64 time=0.215 ms 64 bytes from 169.254.144.71: icmp_seq=2 ttl=64 time=0.456 ms 64 bytes from 169.254.144.71: icmp_seq=3 ttl=64 time=0.448 ms Also, change the data type of 'epf_ntb::db' to 'atomic_64' as multiple doorbell interrupts might trigger at the same time. Signed-off-by: Frank Li <Frank.Li@nxp.com> [mani: added 'pci_epf_' prefix to doorbell IRQ name, minor code cleanups] Signed-off-by: Manivannan Sadhasivam <mani@kernel.org> Link: https://patch.msgid.link/20251015-vntb_msi_doorbell-v6-4-9230298b1910@nxp.com
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 reStructuredText 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.