[PATCH 1/4] pinctrl: mcp23s08: IRQ behavior for open-drain interrupts

[Jan Kundrát <jan.kundrat@xxxxxxxxx>]

The hardware supports three different IRQ modes:
- open drain, i.e., an active-low output which requires an external
  pull-up and supports IRQ line sharing,
- active low, with push-pull output,
- active high, with push-pull output.

My understanding of electronics is limited, but it is "wrong" to connect
different push-pull outpus together. It could sort-of work if the
chips/board actually have some resistors there, but it's an ugly thing
to do.

In the past, this driver did not touch the ODR bit (for open-drain)
operation. During power-on-reset, it is set to zero. Unless some
platform code actually set this bit to one, this means that the code
never supported open drain operation.

This change makes this handling explicit. If you want sharing of the IRQ
line, then use the microchip,irq-open-drain mode and add an external
pull-up.

There's some risk here. If, e.g., the bootloader sets the ODR bit for
some reason, the HW shares the IRQ lines, and nobody changes the DT,
then your HW will suddenly use push-pull driver for the IRQ line. If
there is any other chip on the same lane, the HW might suffer (my chip
survived this when I "tested" this by accident with no bootloader code
to set the ODR bit).

Signed-off-by: Jan Kundrát <jan.kundrat@xxxxxxxxx>
---
 .../bindings/pinctrl/pinctrl-mcp23s08.txt          |  4 ++
 drivers/pinctrl/pinctrl-mcp23s08.c                 | 82 +++++++++++++++-------
 2 files changed, 61 insertions(+), 25 deletions(-)

diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-mcp23s08.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-mcp23s08.txt
index 9c451c20dda4..92aa91027c68 100644
--- a/Documentation/devicetree/bindings/pinctrl/pinctrl-mcp23s08.txt
+++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-mcp23s08.txt
@@ -58,6 +58,10 @@ Optional device specific properties:
         On devices with only one interrupt output this property is useless.
 - microchip,irq-active-high: Sets the INTPOL flag in the IOCON register. This
         configures the IRQ output polarity as active high.
+- microchip,irq-open-drain: Sets the ODR flag in the IOCON register. This
+        configures the IRQ output as active low open-drain and allows sharing
+	of the IRQ line among several chips. Note that irq-active-high and
+	irq-open-drain are mutually exclusive.
 
 Example I2C (with interrupt):
 gpiom1: gpio@20 {
diff --git a/drivers/pinctrl/pinctrl-mcp23s08.c b/drivers/pinctrl/pinctrl-mcp23s08.c
index c017860619d6..186101c575e3 100644
--- a/drivers/pinctrl/pinctrl-mcp23s08.c
+++ b/drivers/pinctrl/pinctrl-mcp23s08.c
@@ -54,9 +54,15 @@
 
 struct mcp23s08;
 
+enum mcp23s08_irq_regime {
+	MCP_IRQ_PULL_LOW,
+	MCP_IRQ_PUSH_UP,
+	MCP_IRQ_OPEN_DRAIN
+};
+
 struct mcp23s08 {
 	u8			addr;
-	bool			irq_active_high;
+	enum mcp23s08_irq_regime	irq_regime;
 	bool			reg_shift;
 
 	u16			irq_rise;
@@ -625,10 +631,17 @@ static int mcp23s08_irq_setup(struct mcp23s08 *mcp)
 	int err;
 	unsigned long irqflags = IRQF_ONESHOT | IRQF_SHARED;
 
-	if (mcp->irq_active_high)
-		irqflags |= IRQF_TRIGGER_HIGH;
-	else
+	switch (mcp->irq_regime) {
+	case MCP_IRQ_PULL_LOW:
 		irqflags |= IRQF_TRIGGER_LOW;
+		break;
+	case MCP_IRQ_PUSH_UP:
+		irqflags |= IRQF_TRIGGER_HIGH;
+		break;
+	case MCP_IRQ_OPEN_DRAIN:
+		irqflags |= IRQF_TRIGGER_LOW | IRQF_SHARED;
+		break;
+	}
 
 	err = devm_request_threaded_irq(chip->parent, mcp->irq, NULL,
 					mcp23s08_irq,
@@ -780,7 +793,7 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev,
 
 	mcp->dev = dev;
 	mcp->addr = addr;
-	mcp->irq_active_high = false;
+	mcp->irq_regime = MCP_IRQ_PULL_LOW;
 
 	mcp->chip.direction_input = mcp23s08_direction_input;
 	mcp->chip.get = mcp23s08_get;
@@ -866,33 +879,52 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev,
 	mcp->irq_controller =
 		device_property_read_bool(dev, "interrupt-controller");
 	if (mcp->irq && mcp->irq_controller) {
-		mcp->irq_active_high =
-			device_property_read_bool(dev,
-					      "microchip,irq-active-high");
+		bool irq_active_high = device_property_read_bool(dev,
+						"microchip,irq-active-high");
+		bool irq_open_drain = device_property_read_bool(dev,
+						"microchip,irq-open-drain");
+		if (irq_active_high && irq_open_drain) {
+			dev_err(dev, "microchip,irq-open-drain and "
+				"microchip,irq-active-high are mutually exclusive\n");
+			ret = -EINVAL;
+			goto fail;
+		} else if (irq_active_high) {
+			mcp->irq_regime = MCP_IRQ_PUSH_UP;
+		} else if (irq_open_drain) {
+			mcp->irq_regime = MCP_IRQ_OPEN_DRAIN;
+		}
 
 		mirror = device_property_read_bool(dev, "microchip,irq-mirror");
 	}
 
-	if ((status & IOCON_SEQOP) || !(status & IOCON_HAEN) || mirror ||
-	     mcp->irq_active_high) {
-		/* mcp23s17 has IOCON twice, make sure they are in sync */
-		status &= ~(IOCON_SEQOP | (IOCON_SEQOP << 8));
-		status |= IOCON_HAEN | (IOCON_HAEN << 8);
-		if (mcp->irq_active_high)
-			status |= IOCON_INTPOL | (IOCON_INTPOL << 8);
-		else
-			status &= ~(IOCON_INTPOL | (IOCON_INTPOL << 8));
+	/* mcp23s17 has IOCON twice, make sure they are in sync */
+	status &= ~(IOCON_SEQOP | (IOCON_SEQOP << 8));
+	status |= IOCON_HAEN | (IOCON_HAEN << 8);
 
-		if (mirror)
-			status |= IOCON_MIRROR | (IOCON_MIRROR << 8);
+	switch (mcp->irq_regime) {
+	case MCP_IRQ_PUSH_UP:
+		status |= IOCON_INTPOL | (IOCON_INTPOL << 8);
+		status &= ~(IOCON_ODR | (IOCON_ODR << 8));
+		break;
+	case MCP_IRQ_PULL_LOW:
+		status &= ~(IOCON_INTPOL | (IOCON_INTPOL << 8));
+		status &= ~(IOCON_ODR | (IOCON_ODR << 8));
+		break;
+	case MCP_IRQ_OPEN_DRAIN:
+		/* ODR overrides INTPOL */
+		status |= IOCON_ODR | (IOCON_ODR << 8);
+		break;
+	}
 
-		if (type == MCP_TYPE_S18 || type == MCP_TYPE_018)
-			status |= IOCON_INTCC | (IOCON_INTCC << 8);
+	if (mirror)
+		status |= IOCON_MIRROR | (IOCON_MIRROR << 8);
 
-		ret = mcp_write(mcp, MCP_IOCON, status);
-		if (ret < 0)
-			goto fail;
-	}
+	if (type == MCP_TYPE_S18 || type == MCP_TYPE_018)
+		status |= IOCON_INTCC | (IOCON_INTCC << 8);
+
+	ret = mcp_write(mcp, MCP_IOCON, status);
+	if (ret < 0)
+		goto fail;
 
 	ret = devm_gpiochip_add_data(dev, &mcp->chip, mcp);
 	if (ret < 0)
-- 
2.14.3


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