Re: [PATCH] powerpc/p1023: set IRQ[4:6, 11] to high level sensitive for PCIe

On Wed, Nov 09, 2011 at 09:27:02AM -0600, Zang Roy-R61911 wrote:

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-----Original Message-----
From: Wood Scott-B07421
Sent: Wednesday, November 09, 2011 0:54 AM
To: Zang Roy-R61911
Cc: Wood Scott-B07421; linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/p1023: set IRQ[4:6, 11] to high level sensitive for
PCIe

Just a note that there's magic to allow the PCIe block to output these
interrupts as either active-high or active-low, depending on how they're
configured at the mpic.

I do not think there is any magic.
On the contrary, it is the mpic/device tree needs to comply with the hardware setting for the interrupt polarity.

The magic is that the PCIe block can generate the interrupt in either
polarity depending on the MPIC setting (or perhaps it bases it on
sampling the pin status during/after reset, but that seems fragile).

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IRQ 4,5,6, 11 are internally tie to low by silicon. To use these interrupts

for PCIe, they need to set high level sensitive.

quoted

It is clear enough for this patch.

It's odd enough that I felt the need to go reading through the docs to
see why such a thing would work at all.

If you consider the normal case, the shared irq pulls up, the PCIe interrupt set to low level sensitive. Anything odd?

The oddity is that active-high works at all for a PCI interrupt, and that
not all the PCIe interrupts have the same polarity.

-Scott