From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Tue, 06 Oct 2015 12:30:19 +0200 Subject: ARM64 PCIe legacy interrupts In-Reply-To: References: Message-ID: <5647794.zPHEyLbn48@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tuesday 06 October 2015 10:17:11 bharat kumar gogada wrote: > I have a confusion in handling legacy interrupts in driver, I'm seeing that > for legacy handling there is separate node being created. Ex: for > pcie-xilinx.c the following node is being used > > pcie_intc: interrupt-controller { > interrupt-controller; > #address-cells = <0>; > #interrupt-cells = <1>; > }; > > Why do we need a separate child node for legacy handling This is a special case where the interrupt lines are not simply passed through to the parent interrupt controller but require an Ack in a separate register. Most sane implementations only need an interrupt-map property that documents how the legacy interrupts are wired to the GIC. > and why is the address cells parameter assigned zero value It means that the interrupt can be identified by the interrupt number itself and does not need to be identified by an address as well. This is true for almost all interrupt controllers. Arnd