Re: [RFC] 85XX: Allow 8259 cascade to share an MPIC interrupt line.

Randy Vinson wrote:

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After processing a possible 8259 interrupt, the 8259 cascade handler
calls handle_fasteoi_irq to perform the actions noted above. However,
with the 8259 cascade handler hooked to the interrupt, the threaded IRQ
handler doesn't recognize it as one of the 4 standard generic IRQ types
and calls the threaded version of do_irq instead of the threaded fasteoi
handler.

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  Ah, that's it!

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Once the threaded do_irq handler completes the action list, it
uses the .end routine to restart the interrupt flow. Pointing .end to
the standard MPIC unmask routine allows it to balance the interrupt mask
operation performed by handle_fasteoi_irq before it scheduled the IRQ
thread.

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  Well, but when MPIC's eoi() method is called then? :-O

It's called from handle_fasteoi_irq as I described in the "basics" ;)

    Indeed, I somehow thought eoi() is out of the threaded exit path of 
handle_fasteoi_irq() -- but it hasn't always been that way!  So, it's probably 
a painful memories of my past quarrel with Ingo over fasteoi breakage that 
played a trick with me here. ;-)

Randy V.

WBR, Sergei