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    SubjectRe: [PATCH 1/2] powerpc/8xx: Fix NR_IRQ bugs and refactor 8xx interrupt controller
    On Mon, Apr 16, 2012 at 5:03 PM, Benjamin Herrenschmidt
    <benh@kernel.crashing.org> wrote:
    > On Mon, 2012-04-16 at 14:13 -0600, Grant Likely wrote:
    >> The mpc8xx driver uses a reference to NR_IRQS that is buggy.  It uses
    >> NR_IRQs for the array size of the ppc_cached_irq_mask bitmap, but
    >> NR_IRQs could be smaller than the number of hardware irqs that
    >> ppc_cached_irq_mask tracks.
    >>
    >> Also, while fixing that problem, it became apparent that the interrupt
    >> controller only supports 32 interrupt numbers, but it is written as if
    >> it supports multiple register banks which is more complicated.
    >>
    >> This patch pulls out the buggy reference to NR_IRQs and fixes the size
    >> of the ppc_cached_irq_mask to match the number of HW irqs.  It also
    >> drops the now-unnecessary code since ppc_cached_irq_mask is no longer
    >> an array.
    >
    > Can you rename ppc_cached_irq_mask while at it ? I think it was written
    > that way because it was all copy/pasted from powermac/pic.c which -does-
    > need it to be an array (and has the same bugs btw) :-)
    >
    > I wonder if we can get rid of the cached mask alltogether... I have the
    > feeling that we could just rely on the irq_desc fields nowadays for
    > that... this code is ancient.

    The irq_desc fields aren't ideal because they are per-irq and would
    need to be &'ed together for each mask/unmask/ack operation. We could
    store something in the irq_domain I suppose, but I'm not convinced it
    is worth it for an interrupt controller that will only ever have one
    instance in the system. If I were to refactor any deeper than I have,
    then I'm move this driver over to use irq_generic_chip instead.

    g.
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