• Marc Zyngier's avatar
    irqchip: Add per-cpu interrupt partitioning library · 9e2c986c
    Marc Zyngier authored
    We've unfortunately started seeing a situation where percpu interrupts
    are partitioned in the system: one arbitrary set of CPUs has an
    interrupt connected to a type of device, while another disjoint
    set of CPUs has the same interrupt connected to another type of device.
    
    This makes it impossible to have a device driver requesting this interrupt
    using the current percpu-interrupt abstraction, as the same interrupt number
    is now potentially claimed by at least two drivers, and we forbid interrupt
    sharing on per-cpu interrupt.
    
    A solution to this is to turn things upside down. Let's assume that our
    system describes all the possible partitions for a given interrupt, and
    give each of them a unique identifier. It is then possible to create
    a namespace where the affinity identifier itself is a form of interrupt
    number. At this point, it becomes easy to implement a set of partitions
    as a cascaded irqchip, each affinity identifier being the HW irq.
    
    This allows us to keep a number of nice properties:
    - Each partition results in a separate percpu-interrupt (with a restrictied
      affinity), which keeps drivers happy.
    - Because the underlying interrupt is still per-cpu, the overhead of
      the indirection can be kept pretty minimal.
    - The core code can ignore most of that crap.
    
    For that purpose, we implement a small library that deals with some of
    the boilerplate code, relying on platform-specific drivers to provide
    a description of the affinity sets and a set of callbacks.
    Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    Cc: Mark Rutland <mark.rutland@arm.com>
    Cc: devicetree@vger.kernel.org
    Cc: Jason Cooper <jason@lakedaemon.net>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Rob Herring <robh+dt@kernel.org>
    Link: http://lkml.kernel.org/r/1460365075-7316-4-git-send-email-marc.zyngier@arm.comSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    9e2c986c