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    SubjectRe: [PATCH] let setup_irq reenable a shared irq
    Hello,

    Thomas Gleixner wrote:
    > On Mon, 28 Apr 2008, Uwe Kleine-König wrote:
    > > > Oh no. There is lots of code in drivers, which does:
    > > >
    > > > disable_irq();
    > > > do_some_protected_stuff();
    > > > enable_irq();
    > > >
    > > > So when the second driver is loaded on another CPU it would see the
    > > > IRQ_DISABLED bit set and unconditionally reenable the interrupt.
    > > >
    > > > This unprotects the protected operation and definitely triggers the
    > > > WARN_ON() in enable_irq() where we check for desc->depth == 0.
    > > mmpf.
    > >
    > > It's not nice to use disable_irq()/enable_irq() in a driver, is it?
    >
    > Well, it's not nice, but it's there (in rather large quantities)
    Ah, and now I finally understood desc->depth ...

    > Subject: genirq: reenable a nobody cared disabled irq when a new driver arrives
    > From: Thomas Gleixner <tglx@linutronix.de>
    > Date: Mon, 28 Apr 2008 17:01:56 +0200
    >
    > Uwe Kleine-Koenig has some strange hardware where one of the shared
    > interrupts can be asserted during boot before the appropriate driver
    > loads. Requesting the shared irq line from another driver results in a
    > spurious interrupt storm which finally disables the interrupt line.
    >
    > I have seen similar behaviour on resume before (the hardware does not
    > work anymore so I can not verify) and this spurious irq issue is
    > raised on a regular base in bugreports.
    >
    > Change the spurious disable logic to increment the disable depth and
    > mark the interrupt with an extra flag which allows us to reenable the
    > interrupt when a new driver arrives which requests the same irq
    > line. In the worst case this will disable the irq again via the
    > spurious trap, but there is a decent chance that the new driver is the
    > one which can handle the already asserted interrupt and makes the box
    > usable again.
    >
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    > Acked-by: Ingo Molnar <mingo@elte.hu>
    > ---
    > include/linux/irq.h | 1 +
    > kernel/irq/manage.c | 49 ++++++++++++++++++++++++++++++++-----------------
    > kernel/irq/spurious.c | 4 ++--
    > 3 files changed, 35 insertions(+), 19 deletions(-)
    >
    > Index: linux-2.6/include/linux/irq.h
    > ===================================================================
    > --- linux-2.6.orig/include/linux/irq.h
    > +++ linux-2.6/include/linux/irq.h
    > @@ -61,6 +61,7 @@ typedef void (*irq_flow_handler_t)(unsig
    > #define IRQ_WAKEUP 0x00100000 /* IRQ triggers system wakeup */
    > #define IRQ_MOVE_PENDING 0x00200000 /* need to re-target IRQ destination */
    > #define IRQ_NO_BALANCING 0x00400000 /* IRQ is excluded from balancing */
    > +#define IRQ_SPURIOUS_DISABLED 0x00400000 /* IRQ was disabled by the spurious trap */
    Is it intended that IRQ_NO_BALANCING == IRQ_SPURIOUS_DISABLED?

    Other than that

    Tested-and-Acked-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>

    Best regards and thanks
    Uwe

    --
    Uwe Kleine-König, Software Engineer
    Digi International GmbH Branch Breisach, Küferstrasse 8, 79206 Breisach, Germany
    Tax: 315/5781/0242 / VAT: DE153662976 / Reg. Amtsgericht Dortmund HRB 13962
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