[PATCH v2 0/3] ARM: sun7i: irqchip: Irqchip driver for NMI

[PATCH v2 0/3] ARM: sun7i: irqchip: Irqchip driver for NMI

[Carlo Caione]

Allwinner A20 SoCs have a special interrupt controller for managing NMI.
Three register are present to (un)mask, control and acknowledge NMI.
These two patches add a new irqchip driver in cascade with GIC.

Changes since v1:
	- added binding document

Carlo Caione (3):
  ARM: sun7i: irqchip: Add irqchip driver for NMI controller
  ARM: sun7i: dts: Add NMI irqchip support
  ARM: sun7i: irqchip: Update the documentation

 .../allwinner,sun7i-sc-nmi.txt                     |  25 +++
 arch/arm/boot/dts/sun7i-a20.dtsi                   |   9 +
 drivers/irqchip/Makefile                           |   1 +
 drivers/irqchip/irq-sun7i-nmi.c                    | 191 +++++++++++++++++++++
 4 files changed, 226 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/interrupt-controller/allwinner,sun7i-sc-nmi.txt
 create mode 100644 drivers/irqchip/irq-sun7i-nmi.c

-- 
1.8.5.2

[PATCH v2 1/3] ARM: sun7i: irqchip: Add irqchip driver for NMI controller

[Carlo Caione]

Allwinner A20 SoCs have special registers to control / (un)mask /
acknowledge NMI. This NMI controller is separated and independent from GIC.
This patch adds a new irqchip to manage NMI.

Signed-off-by: Carlo Caione <carlo.caione@gmail.com>
---
 drivers/irqchip/Makefile        |   1 +
 drivers/irqchip/irq-sun7i-nmi.c | 191 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 192 insertions(+)
 create mode 100644 drivers/irqchip/irq-sun7i-nmi.c

diff --git a/drivers/irqchip/Makefile b/drivers/irqchip/Makefile
index c60b901..d6ad783 100644
--- a/drivers/irqchip/Makefile
+++ b/drivers/irqchip/Makefile
@@ -11,6 +11,7 @@ obj-$(CONFIG_METAG_PERFCOUNTER_IRQS)	+= irq-metag.o
 obj-$(CONFIG_ARCH_MOXART)		+= irq-moxart.o
 obj-$(CONFIG_ORION_IRQCHIP)		+= irq-orion.o
 obj-$(CONFIG_ARCH_SUNXI)		+= irq-sun4i.o
+obj-$(CONFIG_ARCH_SUNXI)		+= irq-sun7i-nmi.o
 obj-$(CONFIG_ARCH_SPEAR3XX)		+= spear-shirq.o
 obj-$(CONFIG_ARM_GIC)			+= irq-gic.o
 obj-$(CONFIG_ARM_NVIC)			+= irq-nvic.o
diff --git a/drivers/irqchip/irq-sun7i-nmi.c b/drivers/irqchip/irq-sun7i-nmi.c
new file mode 100644
index 0000000..c36a236
--- /dev/null
+++ b/drivers/irqchip/irq-sun7i-nmi.c
@@ -0,0 +1,191 @@
+/*
+ * Allwinner A20 SoCs NMI IRQ chip driver.
+ *
+ * Carlo Caione <carlo.caione@gmail.com>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2.  This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+
+#include <linux/bitops.h>
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/irq.h>
+#include <linux/interrupt.h>
+#include <linux/irqdomain.h>
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+#include <linux/of_platform.h>
+#include <linux/irqchip/chained_irq.h>
+#include "irqchip.h"
+
+#define SUN7I_NMI_IRQ_CTRL_REG	0x00
+#define SUN7I_NMI_IRQ_PEND_REG	0x04
+#define SUN7I_NMI_IRQ_EN_REG	0x08
+
+#define SUN7I_NMI_SRC_TYPE_MASK	0x00000003
+
+enum {
+	SUN7I_SRC_TYPE_LEVEL_LOW = 0,
+	SUN7I_SRC_TYPE_EDGE_FALLING,
+	SUN7I_SRC_TYPE_LEVEL_HIGH,
+	SUN7I_SRC_TYPE_EDGE_RISING,
+};
+
+/*
+ * Ack level interrupts right before unmask
+ *
+ * In case of level-triggered interrupt, IRQ line must be acked before it
+ * is unmasked or else a double-interrupt is triggered
+ */
+
+static void sun7i_sc_nmi_ack_and_unmask(struct irq_data *d)
+{
+	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(d);
+	struct irq_chip_type *ct = irq_data_get_chip_type(d);
+	u32 mask = d->mask;
+
+	if (irqd_get_trigger_type(d) & IRQ_TYPE_LEVEL_MASK)
+		ct->chip.irq_ack(d);
+
+	irq_gc_lock(gc);
+	irq_reg_writel(mask, gc->reg_base + ct->regs.mask);
+	irq_gc_unlock(gc);
+}
+
+static inline void sun7i_sc_nmi_write(struct irq_chip_generic *gc, u32 off,
+				      u32 val)
+{
+	irq_reg_writel(val, gc->reg_base + off);
+}
+
+static inline u32 sun7i_sc_nmi_read(struct irq_chip_generic *gc, u32 off)
+{
+	return irq_reg_readl(gc->reg_base + off);
+}
+
+static void sun7i_sc_nmi_handle_irq(unsigned int irq, struct irq_desc *desc)
+{
+	struct irq_domain *domain = irq_desc_get_handler_data(desc);
+	struct irq_chip *chip = irq_get_chip(irq);
+	unsigned int virq = irq_find_mapping(domain, 0);
+
+	chained_irq_enter(chip, desc);
+	generic_handle_irq(virq);
+	chained_irq_exit(chip, desc);
+}
+
+static int sun7i_sc_nmi_set_type(struct irq_data *data, unsigned int flow_type)
+{
+	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(data);
+	u32 src_type_reg;
+	unsigned int src_type;
+
+	irq_gc_lock(gc);
+
+	switch (flow_type & IRQF_TRIGGER_MASK) {
+	case IRQ_TYPE_EDGE_FALLING:
+		src_type = SUN7I_SRC_TYPE_EDGE_FALLING;
+		break;
+	case IRQ_TYPE_EDGE_RISING:
+		src_type = SUN7I_SRC_TYPE_EDGE_RISING;
+		break;
+	case IRQ_TYPE_LEVEL_HIGH:
+		src_type = SUN7I_SRC_TYPE_LEVEL_HIGH;
+		break;
+	case IRQ_TYPE_NONE:
+	case IRQ_TYPE_LEVEL_LOW:
+		src_type = SUN7I_SRC_TYPE_LEVEL_LOW;
+		break;
+	default:
+		irq_gc_unlock(gc);
+		pr_err("%s: Cannot assign multiple trigger modes to IRQ %d.\n",
+			__func__, data->irq);
+		return -EBADR;
+	}
+
+	irqd_set_trigger_type(data, flow_type);
+	irq_setup_alt_chip(data, flow_type);
+
+	src_type_reg = sun7i_sc_nmi_read(gc, SUN7I_NMI_IRQ_CTRL_REG);
+	src_type_reg &= ~SUN7I_NMI_SRC_TYPE_MASK;
+	src_type_reg |= src_type;
+	sun7i_sc_nmi_write(gc, SUN7I_NMI_IRQ_CTRL_REG, src_type_reg);
+
+	irq_gc_unlock(gc);
+
+	return IRQ_SET_MASK_OK;
+}
+
+static int __init sun7i_sc_nmi_irq_init(struct device_node *node,
+					struct device_node *parent)
+{
+	struct irq_domain *domain;
+	struct irq_chip_generic *gc;
+	unsigned int irq;
+	unsigned int clr = IRQ_NOREQUEST | IRQ_NOPROBE | IRQ_NOAUTOEN;
+	int ret;
+
+	domain = irq_domain_add_linear(node, 1, &irq_generic_chip_ops, NULL);
+	if (!domain) {
+		pr_err("%s: Could not register interrupt domain.\n", node->name);
+		return -ENOMEM;
+	}
+
+	ret = irq_alloc_domain_generic_chips(domain, 1, 2, node->name,
+					     handle_level_irq, clr, 0,
+					     IRQ_GC_INIT_MASK_CACHE);
+	if (ret) {
+		 pr_err("%s: Could not allocate generic interrupt chip.\n",
+			 node->name);
+		 goto fail_irqd_remove;
+	}
+
+	irq = irq_of_parse_and_map(node, 0);
+	if (irq <= 0) {
+		pr_err("%s: unable to parse irq\n", node->name);
+		ret = -EINVAL;
+		goto fail_irqd_remove;
+	}
+
+	gc = irq_get_domain_generic_chip(domain, 0);
+	gc->reg_base = of_iomap(node, 0);
+	if (!gc->reg_base) {
+		pr_err("%s: unable to map resource\n", node->name);
+		ret = -ENOMEM;
+		goto fail_irqd_remove;
+	}
+
+	gc->chip_types[0].type			= IRQ_TYPE_LEVEL_MASK;
+	gc->chip_types[0].chip.irq_ack		= irq_gc_ack_set_bit;
+	gc->chip_types[0].chip.irq_mask		= irq_gc_mask_clr_bit;
+	gc->chip_types[0].chip.irq_unmask	= sun7i_sc_nmi_ack_and_unmask;
+	gc->chip_types[0].chip.irq_set_type	= sun7i_sc_nmi_set_type;
+	gc->chip_types[0].regs.ack		= SUN7I_NMI_IRQ_PEND_REG;
+	gc->chip_types[0].regs.mask		= SUN7I_NMI_IRQ_EN_REG;
+
+	gc->chip_types[1].type			= IRQ_TYPE_EDGE_BOTH;
+	gc->chip_types[1].chip.name		= gc->chip_types[0].chip.name;
+	gc->chip_types[1].chip.irq_ack		= irq_gc_ack_set_bit;
+	gc->chip_types[1].chip.irq_mask		= irq_gc_mask_clr_bit;
+	gc->chip_types[1].chip.irq_unmask	= sun7i_sc_nmi_ack_and_unmask;
+	gc->chip_types[1].chip.irq_set_type	= sun7i_sc_nmi_set_type;
+	gc->chip_types[1].regs.ack		= SUN7I_NMI_IRQ_PEND_REG;
+	gc->chip_types[1].regs.mask		= SUN7I_NMI_IRQ_EN_REG;
+	gc->chip_types[1].handler		= handle_edge_irq;
+
+	irq_set_handler_data(irq, domain);
+	irq_set_chained_handler(irq, sun7i_sc_nmi_handle_irq);
+
+	sun7i_sc_nmi_write(gc, SUN7I_NMI_IRQ_EN_REG, 0);
+	sun7i_sc_nmi_write(gc, SUN7I_NMI_IRQ_PEND_REG, 0x1);
+
+	return 0;
+
+fail_irqd_remove:
+	irq_domain_remove(domain);
+	return ret;
+}
+
+IRQCHIP_DECLARE(sun7i_sc_nmi, "allwinner,sun7i-sc-nmi", sun7i_sc_nmi_irq_init);
-- 
1.8.5.2

[PATCH v2 2/3] ARM: sun7i: dts: Add NMI irqchip support

[Carlo Caione]

This patch adds DTS entry for NMI controller as child of GIC.

Signed-off-by: Carlo Caione <carlo.caione@gmail.com>
---
 arch/arm/boot/dts/sun7i-a20.dtsi | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm/boot/dts/sun7i-a20.dtsi b/arch/arm/boot/dts/sun7i-a20.dtsi
index 4c25f81..89e93da 100644
--- a/arch/arm/boot/dts/sun7i-a20.dtsi
+++ b/arch/arm/boot/dts/sun7i-a20.dtsi
@@ -310,6 +310,15 @@
 		#size-cells = <1>;
 		ranges;
 
+		nmi_intc: sc-nmi-intc at 01c00030 {
+			compatible = "allwinner,sun7i-sc-nmi";
+			interrupt-controller;
+			#interrupt-cells = <2>;
+			reg = <0x01c00030 0x0c>;
+			interrupt-parent = <&gic>;
+			interrupts = <0 0 1>;
+		};
+
 		emac: ethernet at 01c0b000 {
 			compatible = "allwinner,sun4i-emac";
 			reg = <0x01c0b000 0x1000>;
-- 
1.8.5.2

[PATCH v2 3/3] ARM: sun7i: irqchip: Update the documentation

[Carlo Caione]

Added documentation for NMI irqchip.

Signed-off-by: Carlo Caione <carlo.caione@gmail.com>
---
 .../allwinner,sun7i-sc-nmi.txt                     | 25 ++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/interrupt-controller/allwinner,sun7i-sc-nmi.txt

diff --git a/Documentation/devicetree/bindings/interrupt-controller/allwinner,sun7i-sc-nmi.txt b/Documentation/devicetree/bindings/interrupt-controller/allwinner,sun7i-sc-nmi.txt
new file mode 100644
index 0000000..8ba0124
--- /dev/null
+++ b/Documentation/devicetree/bindings/interrupt-controller/allwinner,sun7i-sc-nmi.txt
@@ -0,0 +1,25 @@
+Allwinner Sunxi NMI Controller
+==============================
+
+Required properties:
+
+- compatible : should be "allwinner,sun7i-sc-nmi"
+- reg : Specifies base physical address and size of the registers.
+- interrupt-controller : Identifies the node as an interrupt controller
+- #interrupt-cells : Specifies the number of cells needed to encode an
+  interrupt source. The value shall be 2.
+- interrupt-parent: Specifies the parent interrupt controller.
+- interrupts: Specifies the list of interrupt lines which are handled by
+  the interrupt controller in the parent controller's notation. This value
+  shall be the NMI.
+
+Example:
+
+sc-nmi-intc at 01c00030 {
+	compatible = "allwinner,sun7i-sc-nmi";
+	interrupt-controller;
+	#interrupt-cells = <2>;
+	reg = <0x01c00030 0x0c>;
+	interrupt-parent = <&gic>;
+	interrupts = <0 0 1>;
+};
-- 
1.8.5.2

[PATCH v2 0/3] ARM: sun7i: irqchip: Irqchip driver for NMI

[Carlo Caione]

On Mon, Jan 6, 2014 at 6:41 PM, Carlo Caione <carlo.caione@gmail.com> wrote:
> Allwinner A20 SoCs have a special interrupt controller for managing NMI.
> Three register are present to (un)mask, control and acknowledge NMI.
> These two patches add a new irqchip driver in cascade with GIC.
>
> Changes since v1:
>         - added binding document

Ping?

[PATCH v2 3/3] ARM: sun7i: irqchip: Update the documentation

[Arnd Bergmann]

On Monday 06 January 2014, Carlo Caione wrote:
> +Allwinner Sunxi NMI Controller
> +==============================
> +
> +Required properties:
> +
> +- compatible : should be "allwinner,sun7i-sc-nmi"
> +- reg : Specifies base physical address and size of the registers.
> +- interrupt-controller : Identifies the node as an interrupt controller
> +- #interrupt-cells : Specifies the number of cells needed to encode an
> +  interrupt source. The value shall be 2.

I think you should list what the two cells are so users know what to
put in the irq specifier.

> +sc-nmi-intc at 01c00030 {
> +       compatible = "allwinner,sun7i-sc-nmi";
> +       interrupt-controller;
> +       #interrupt-cells = <2>;
> +       reg = <0x01c00030 0x0c>;
> +       interrupt-parent = <&gic>;
> +       interrupts = <0 0 1>;
> +};

Is <0 0 1> the correct representation of the NMI? This question has recently
come up on IRC and I didn't know the answer at the time.

	Arnd

[PATCH v2 3/3] ARM: sun7i: irqchip: Update the documentation

[Carlo Caione]

On Wed, Jan 8, 2014 at 12:29 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Monday 06 January 2014, Carlo Caione wrote:
>> +Allwinner Sunxi NMI Controller
>> +==============================
>> +
>> +Required properties:
>> +
>> +- compatible : should be "allwinner,sun7i-sc-nmi"
>> +- reg : Specifies base physical address and size of the registers.
>> +- interrupt-controller : Identifies the node as an interrupt controller
>> +- #interrupt-cells : Specifies the number of cells needed to encode an
>> +  interrupt source. The value shall be 2.
>
> I think you should list what the two cells are so users know what to
> put in the irq specifier.

Agree, I'll fix in v3

>> +sc-nmi-intc at 01c00030 {
>> +       compatible = "allwinner,sun7i-sc-nmi";
>> +       interrupt-controller;
>> +       #interrupt-cells = <2>;
>> +       reg = <0x01c00030 0x0c>;
>> +       interrupt-parent = <&gic>;
>> +       interrupts = <0 0 1>;
>> +};
>
> Is <0 0 1> the correct representation of the NMI? This question has recently
> come up on IRC and I didn't know the answer at the time.

Why shouldn't it be a correct representation? I think I missed the
discussion on IRC.
Actually I already have a MFD driver using this irqchip without any problems.

Thanks,

--
Carlo Caione

[PATCH v2 3/3] ARM: sun7i: irqchip: Update the documentation

[Hans de Goede]

Hi,

On 01/08/2014 12:49 PM, Carlo Caione wrote:
> On Wed, Jan 8, 2014 at 12:29 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Monday 06 January 2014, Carlo Caione wrote:
>>> +Allwinner Sunxi NMI Controller
>>> +==============================
>>> +
>>> +Required properties:
>>> +
>>> +- compatible : should be "allwinner,sun7i-sc-nmi"
>>> +- reg : Specifies base physical address and size of the registers.
>>> +- interrupt-controller : Identifies the node as an interrupt controller
>>> +- #interrupt-cells : Specifies the number of cells needed to encode an
>>> +  interrupt source. The value shall be 2.
>>
>> I think you should list what the two cells are so users know what to
>> put in the irq specifier.
>
> Agree, I'll fix in v3
>
>>> +sc-nmi-intc at 01c00030 {
>>> +       compatible = "allwinner,sun7i-sc-nmi";
>>> +       interrupt-controller;
>>> +       #interrupt-cells = <2>;
>>> +       reg = <0x01c00030 0x0c>;
>>> +       interrupt-parent = <&gic>;
>>> +       interrupts = <0 0 1>;
>>> +};
>>
>> Is <0 0 1> the correct representation of the NMI? This question has recently
>> come up on IRC and I didn't know the answer at the time.
>
> Why shouldn't it be a correct representation? I think I missed the
> discussion on IRC.

I did not see the discussion on irc either, but this almost certainly
should be <0 0 4>, as all interrupts on sun7i are level sensitive, not
edge sensitive, making it <0 0 1> and thus edge sensitive can cause
lost interrupts if an interrupt fires between the handler has reading
the interrupt status register, and it writing it to clear the bits it
has seen. In this case the interrupt line stays high, but the interrupt
handler won't get re-run when configured for level interrupts.

Regards,

Hans

[PATCH v2 3/3] ARM: sun7i: irqchip: Update the documentation

[Arnd Bergmann]

On Wednesday 08 January 2014 12:49:10 Carlo Caione wrote:
> >> +sc-nmi-intc at 01c00030 {
> >> +       compatible = "allwinner,sun7i-sc-nmi";
> >> +       interrupt-controller;
> >> +       #interrupt-cells = <2>;
> >> +       reg = <0x01c00030 0x0c>;
> >> +       interrupt-parent = <&gic>;
> >> +       interrupts = <0 0 1>;
> >> +};
> >
> > Is <0 0 1> the correct representation of the NMI? This question has recently
> > come up on IRC and I didn't know the answer at the time.
> 
> Why shouldn't it be a correct representation? I think I missed the
> discussion on IRC.

For all I know, the NMI and the IRQ input to the CPU are separate pins,
so the NMI irqchip is not actually cascaded to the GIC, and SPI-0
might in fact be a different interrupt source.

	Arnd

[linux-sunxi] Re: [PATCH v2 3/3] ARM: sun7i: irqchip: Update the documentation

[Carlo Caione]

On Wed, Jan 8, 2014 at 2:09 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wednesday 08 January 2014 12:49:10 Carlo Caione wrote:
>> >> +sc-nmi-intc at 01c00030 {
>> >> +       compatible = "allwinner,sun7i-sc-nmi";
>> >> +       interrupt-controller;
>> >> +       #interrupt-cells = <2>;
>> >> +       reg = <0x01c00030 0x0c>;
>> >> +       interrupt-parent = <&gic>;
>> >> +       interrupts = <0 0 1>;
>> >> +};
>> >
>> > Is <0 0 1> the correct representation of the NMI? This question has recently
>> > come up on IRC and I didn't know the answer at the time.
>>
>> Why shouldn't it be a correct representation? I think I missed the
>> discussion on IRC.
>
> For all I know, the NMI and the IRQ input to the CPU are separate pins,
> so the NMI irqchip is not actually cascaded to the GIC, and SPI-0
> might in fact be a different interrupt source.

In Allwinner A20/A31 SoCs NMI controller is an independent module
external and in cascade with the GIC. It catches the NMI pin's state
and generates irq to GIC.
(therefore NMI is not really not Non-maskable but it is a normal interrupt).
Here is an ascii-plot of the system (thanks to Maxime and the
Allwinner engineers for this)

           +---------+            +-----------+
           |         +------------+ FIQ       |
           |   GIC   |            |           |
           |         +------------+ INT   CPU |
           +--+---+--+            |           |
              |   |               |           |
              |   +------+        |           |
              |          |        |           |
 +-----+   +--+--+   +---+---+    |           |
 | AXP +-+-+ NMI +   | ALARM |    |           |
 +-----+ | +-----+   +---+---+    +-----------+
         |               |
         +---------------+

Best,

--
Carlo Caione

[PATCH v2 3/3] ARM: sun7i: irqchip: Update the documentation

[Carlo Caione]

On Wed, Jan 8, 2014 at 2:03 PM, Hans de Goede <hdegoede@redhat.com> wrote:
> Hi,
>
>
> On 01/08/2014 12:49 PM, Carlo Caione wrote:
>>
>> On Wed, Jan 8, 2014 at 12:29 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>>>
>>> On Monday 06 January 2014, Carlo Caione wrote:
>>>>
>>>> +Allwinner Sunxi NMI Controller
>>>> +==============================
>>>> +
>>>> +Required properties:
>>>> +
>>>> +- compatible : should be "allwinner,sun7i-sc-nmi"
>>>> +- reg : Specifies base physical address and size of the registers.
>>>> +- interrupt-controller : Identifies the node as an interrupt controller
>>>> +- #interrupt-cells : Specifies the number of cells needed to encode an
>>>> +  interrupt source. The value shall be 2.
>>>
>>>
>>> I think you should list what the two cells are so users know what to
>>> put in the irq specifier.
>>
>>
>> Agree, I'll fix in v3
>>
>>>> +sc-nmi-intc at 01c00030 {
>>>> +       compatible = "allwinner,sun7i-sc-nmi";
>>>> +       interrupt-controller;
>>>> +       #interrupt-cells = <2>;
>>>> +       reg = <0x01c00030 0x0c>;
>>>> +       interrupt-parent = <&gic>;
>>>> +       interrupts = <0 0 1>;
>>>> +};
>>>
>>>
>>> Is <0 0 1> the correct representation of the NMI? This question has
>>> recently
>>> come up on IRC and I didn't know the answer at the time.
>>
>>
>> Why shouldn't it be a correct representation? I think I missed the
>> discussion on IRC.
>
>
> I did not see the discussion on irc either, but this almost certainly
> should be <0 0 4>, as all interrupts on sun7i are level sensitive, not
> edge sensitive, making it <0 0 1> and thus edge sensitive can cause
> lost interrupts if an interrupt fires between the handler has reading
> the interrupt status register, and it writing it to clear the bits it
> has seen. In this case the interrupt line stays high, but the interrupt
> handler won't get re-run when configured for level interrupts.

Ouch, right! fix coming in v3.

Thanks,

--
Carlo Caione

[linux-sunxi] Re: [PATCH v2 3/3] ARM: sun7i: irqchip: Update the documentation

[Arnd Bergmann]

On Thursday 09 January 2014, Carlo Caione wrote:
> In Allwinner A20/A31 SoCs NMI controller is an independent module
> external and in cascade with the GIC. It catches the NMI pin's state
> and generates irq to GIC.
> (therefore NMI is not really not Non-maskable but it is a normal interrupt).
> Here is an ascii-plot of the system (thanks to Maxime and the
> Allwinner engineers for this)
> 
>            +---------+            +-----------+
>            |         +------------+ FIQ       |
>            |   GIC   |            |           |
>            |         +------------+ INT   CPU |
>            +--+---+--+            |           |
>               |   |               |           |
>               |   +------+        |           |
>               |          |        |           |
>  +-----+   +--+--+   +---+---+    |           |
>  | AXP +-+-+ NMI +   | ALARM |    |           |
>  +-----+ | +-----+   +---+---+    +-----------+
>          |               |
>          +---------------+

Ah, cool. That certianly makes sense now. Thanks for the explanation.

	Arnd