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If flag IRQCHIP_ONESHOT_SAFE isn't set for an irqchip and we have a threaded interrupt with no primary handler, flag IRQF_ONESHOT needs to be set for the interrupt, causing some overhead in the threaded interrupt handler. For more detailed explanation also check following comment in __setup_irq(): The interrupt was requested with handler = NULL, so we use the default primary handler for it. But it does not have the oneshot flag set. In combination with level interrupts this is deadly, because the default primary handler just wakes the thread, then the irq lines is reenabled, but the device still has the level irq asserted. Rinse and repeat.... While this works for edge type interrupts, we play it safe and reject unconditionally because we can't say for sure which type this interrupt really has. The type flags are unreliable as the underlying chip implementation can override them. Another comment in __setup_irq() gives a hint already that this overhead can be avoided for PCI-MSI: Some irq chips like MSI based interrupts are per se one shot safe. Check the chip flags, so we can avoid the unmask dance at the end of the threaded handler for those. Following this let's mark all PCI-MSI irqchips as oneshot-safe. See also discussion here: https://lkml.kernel.org/r/alpine.DEB.2.21.1808032136490.1658@nanos.tec.linutronix.de Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.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 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.