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    Subject[patch V2 42/46] genirq/proc: Take buslock on affinity write
    Until now interrupt chips which support setting affinity are nit locking
    the associated bus lock for two reasons:

    - All chips which support affinity setting do not use buslock because they just
    can operated directly on the hardware.

    - All chips which use buslock do not support affinity setting because
    their interrupt chips are not capable. These chips are usually connected
    over a bus like I2C, SPI etc. and have an interrupt output which is
    conneted to CPU interrupt of some sort. So there is no way to set the
    affinity on the chip itself.

    Upcoming hardware which is PCIE based sports a non standard MSI(X) variant
    which stores the MSI message in RAM which is associated to e.g. a device
    queue. The device manages this RAM and writes have to be issued via command
    queues or similar mechanisms which is obviously not possible from interrupt
    disabled, raw spinlock held context.

    The buslock mechanism of irq chips can be utilized to support that. The
    affinity write to the chip writes to shadow state, marks it pending and the
    irq chip's irq_bus_sync_unlock() callback handles the command queue and
    wait for completion similar to the other chip operations on I2C or SPI
    busses.

    Change the locking in irq_set_affinity() to bus_lock/unlock to help with
    that. There are a few other callers than the proc interface, but none of
    them is affected by this change as none of them affects an irq chip with
    bus lock support.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    V2: New patch
    ---
    kernel/irq/manage.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)
    --- a/kernel/irq/manage.c
    +++ b/kernel/irq/manage.c
    @@ -373,16 +373,16 @@ int irq_set_affinity_locked(struct irq_d

    int __irq_set_affinity(unsigned int irq, const struct cpumask *mask, bool force)
    {
    - struct irq_desc *desc = irq_to_desc(irq);
    + struct irq_desc *desc;
    unsigned long flags;
    int ret;

    + desc = irq_get_desc_buslock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
    if (!desc)
    return -EINVAL;

    - raw_spin_lock_irqsave(&desc->lock, flags);
    ret = irq_set_affinity_locked(irq_desc_get_irq_data(desc), mask, force);
    - raw_spin_unlock_irqrestore(&desc->lock, flags);
    + irq_put_desc_busunlock(desc, flags);
    return ret;
    }

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