linux-kernel - Re: Need clarity on PCIe MSI interrupt in device tree

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Message-ID: <fb1ae45f-1682-c523-ed02-48ca1b890791@arm.com>
Date:   Wed, 4 Jan 2017 08:29:06 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     valmiki <valmikibow@...il.com>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Cc:     helgaas@...nel.org, arnd@...db.de, mark.rutland@....com
Subject: Re: Need clarity on PCIe MSI interrupt in device tree

On 04/01/17 03:17, valmiki wrote:
> Hi,
> 
> I have confusion on MSI interrupt flags in PCIe documetation.
> 
> MSI interrupts are edge triggered, but i see some controllers use 
> Ex:tegra <0 99 0x4>, here interrupt flags show 0x4 which means level 
> sensitive as per include/dt-bindings/interrupt-controller/irq.h.
> 
> May i know why is it like this, why MSI depicted as level sensitive in 
> device tree.

They are not. MSIs are *not* present in the device tree at all.

What you have here is the cascade interrupt from an MSI controller to
another interrupt controller (probably a GICv2), and that particular
interrupt is level triggered. Which is perfectly fine if that's the
signalling method between the two controllers.

This doesn't in any way reflect how MSIs are signalled.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...