linux-kernel - Using irq-crossbar.c

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Date:	Fri, 10 Jun 2016 17:37:30 +0200
From:	Sebastian Frias <sf84@...oste.net>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Marc Zyngier <marc.zyngier@....com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Sricharan R <r.sricharan@...com>, Mason <slash.tmp@...e.fr>,
	Måns Rullgård <mans@...sr.com>
Subject: Using irq-crossbar.c

Hi,

We are trying to write a driver for an interrupt controller (actually more of a crossbar) for an ARM-based SoC.
This IRQ crossbar has 128 inputs and 24 outputs, the outputs are connected directly to the GIC.
The idea is that the GIC handles everything, and just request a mapping from an IRQ number (0...127, from a device's DT entry) into one of its 24 input lines.

By looking at current code (4.7-rc1) there seems to be a driver (drivers/irqchip/irq-crossbar.c) that provides similar functionality.
The driver uses hierarchical irq domains (since commit 783d31863fb8 "irqchip: crossbar: Convert dra7 crossbar to stacked domains") which we believe we don't need because the only controller is the GIC.
However the API used previously, register_routable_domain_ops(), was removed with commit a5561c3e845c "irqchip: gic: Get rid of routable domain".

Trying to use the driver with hierarchical domains (after modifications for our SoC), results on the kernel being blocked at some point:

[    0.041524] ThumbEE CPU extension supported.
[    0.041589] Registering SWP/SWPB emulation handler
[    0.052022] Freeing unused kernel memory: 12364K (c029b000 - c0eae000)
[    0.074084] random: dbus-uuidgen urandom read with 0 bits of entropy available

We've put logs on the different domain_ops calls (alloc, free, translate) but they are not called, even if the DT is supposed to tell devices to take interrupts from this controller (*).

Do you have suggestions on what APIs should be used, further reading/examples and/or pointers on how debug this (logs to enable, things to look for, etc.)?

Thanks in advance.
Best regards,

Sebastian

(*):
here's the diff on our DT:

--- tango4-common.dtsi	2016-06-10 16:23:08.244246017 +0200
+++ tangox_irqv2-common.dtsi	2016-06-10 16:24:01.212588737 +0200
@@ -47,7 +47,7 @@

 	soc {
 		compatible = "simple-bus";
-		interrupt-parent = <&irq0>;
+		interrupt-parent = <&irq_mux>;
 		#address-cells = <1>;
 		#size-cells = <1>;
 		ranges;
@@ -75,7 +75,7 @@
 		uart: serial@...00 {
 			compatible = "ralink,rt2880-uart";
 			reg = <0x10700 0x30>;
-			interrupts = <1 IRQ_TYPE_LEVEL_HIGH>;
+			interrupts = <GIC_SPI 1 IRQ_TYPE_LEVEL_HIGH>;
 			clock-frequency = <7372800>;
 			reg-shift = <2>;
 		};
@@ -83,10 +83,11 @@
 		eth0: ethernet@...00 {
 			compatible = "sigma,smp8734-ethernet";
 			reg = <0x26000 0x800>;
-			interrupts = <38 IRQ_TYPE_LEVEL_HIGH>;
+			interrupts = <GIC_SPI 38 IRQ_TYPE_LEVEL_HIGH>;
 			clocks = <&clkgen 1>;
 		};

+#if 0
 		intc: interrupt-controller@...00 {
 			compatible = "sigma,smp8642-intc";
 			reg = <0x6e000 0x400>;
@@ -117,5 +118,16 @@
 				interrupts = <GIC_SPI 4 IRQ_TYPE_LEVEL_HIGH>;
 			};
 		};
+#else
+		irq_mux: irq_mux@...00 {
+			 compatible = "sigma,smp-irq-mux";
+			 reg = <0x6f800 0x400>;
+			 interrupt-controller;
+			 interrupt-parent = <&gic>;
+			 irqs-reserved = <2 3 4 125 126 127>;
+		};
+
+#endif
+
 	};
 };