On Tue, Oct 02, 2007 at 09:14:21AM +1000, Benjamin Herrenschmidt wrote:

On Tue, 2007-09-25 at 18:34 +0400, Anton Vorontsov wrote:

quoted

set_irq_chained_handler overwrites MPIC's handle_irq function
(handle_fasteoi_irq) thus MPIC never gets eoi event from the
cascaded IRQ. This situation hangs MPIC on MPC8568E.

Patch adds flow level "end" handler to the MPIC, and QEIC calls
it when QEIC's interrupt processing finished.

Signed-off-by: Anton Vorontsov <redacted>

Not sure if I already NAKed it on the list, so if I didn't here's it :-)

The proper way of doing that is to have the cascade handler perform the
EOI call to mpic.

Exactly, this is what that patch is trying to do. QEIC cascade handler is
calling mpic's eoi() (end() actually, as it's flow level, but end == eoi.
Is it main objection? Ok, I can get rid of it, and use chip level eoi()
directly).

Look at how it's done for i8259 mpic cascade handlers.

void pseries_8259_cascade(unsigned int irq, struct irq_desc *desc)
{       
        unsigned int cascade_irq = i8259_irq();
        if (cascade_irq != NO_IRQ)
                generic_handle_irq(cascade_irq);
        desc->chip->eoi(irq);
}
...
set_irq_chained_handler(cascade_irq, pseries_8259_cascade);

Quite similar... except that it's written in the board file.

Basically, when doing a cascade nowadays, you can either just do a
normal request_irq() of the cascade, in which case your handler don't
have to care about the parent controller at all, but you get various
limitations and/or overhead from being a full blown interrupt handler,

Though viable, but not an option.

or you can use the chained handler mechanism which is a "shortcut" but
implies that your cascade handler "knows" what needs to be done to the
parent (and thus is specific to the combination parent/child).

Yup, exactly. Actually, QEIC's cascade handlers do not really know
what needs to be done, but they're good at guessing (if (chip->eoi)).

Sure, I can place board-specific QEIC handlers in the board file, but
that will be quite big code duplication for all machines using QEIC.

Cheers,
Ben.

Thanks,

-- 
Anton Vorontsov
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