gpio: pca953x: Add support for TI TCA6418

The TI TCA6418 is a 18-channel I2C I/O expander. It is slightly
different to other models from the same family, such as TCA6416,
but has enough in common with them to make it work with just a
few tweaks, which are explained in the code's documentation.

Signed-off-by: Maria Garcia <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-pca953x.c

···
 #define PCA953X_INVERT		0x02
 #define PCA953X_DIRECTION	0x03
 
+#define TCA6418_INPUT		0x14
+#define TCA6418_OUTPUT		0x17
+#define TCA6418_DIRECTION	0x23
+
 #define REG_ADDR_MASK		GENMASK(5, 0)
 #define REG_ADDR_EXT		BIT(6)
 #define REG_ADDR_AI		BIT(7)
···
 #define PCA953X_TYPE		BIT(12)
 #define PCA957X_TYPE		BIT(13)
 #define PCAL653X_TYPE		BIT(14)
-#define PCA_TYPE_MASK		GENMASK(15, 12)
+#define TCA6418_TYPE		BIT(16)
+#define PCA_TYPE_MASK		GENMASK(16, 12)
 
 #define PCA_CHIP_TYPE(x)	((x) & PCA_TYPE_MASK)
 
···
 	{ "pca6107", 8  | PCA953X_TYPE | PCA_INT, },
 	{ "tca6408", 8  | PCA953X_TYPE | PCA_INT, },
 	{ "tca6416", 16 | PCA953X_TYPE | PCA_INT, },
+	{ "tca6418", 18 | TCA6418_TYPE | PCA_INT, },
 	{ "tca6424", 24 | PCA953X_TYPE | PCA_INT, },
 	{ "tca9538", 8  | PCA953X_TYPE | PCA_INT, },
 	{ "tca9539", 16 | PCA953X_TYPE | PCA_INT, },
···
 	.invert = PCA957X_INVRT,
 };
 
+static const struct pca953x_reg_config tca6418_regs = {
+	.direction = TCA6418_DIRECTION,
+	.output = TCA6418_OUTPUT,
+	.input = TCA6418_INPUT,
+	.invert = 0xFF, /* Does not apply */
+};
+
 struct pca953x_chip {
 	unsigned gpio_start;
 	struct mutex i2c_lock;
···
 static int pca953x_bank_shift(struct pca953x_chip *chip)
 {
 	return fls((chip->gpio_chip.ngpio - 1) / BANK_SZ);
+}
+
+/*
+ * Helper function to get the correct bit mask for a given offset and chip type.
+ * The TCA6418's input, output, and direction banks have a peculiar bit order:
+ * the first byte uses reversed bit order, while the second byte uses standard order.
+ */
+static inline u8 pca953x_get_bit_mask(struct pca953x_chip *chip, unsigned int offset)
+{
+	unsigned int bit_pos_in_bank = offset % BANK_SZ;
+	int msb = BANK_SZ - 1;
+
+	if (PCA_CHIP_TYPE(chip->driver_data) == TCA6418_TYPE && offset <= msb)
+		return BIT(msb - bit_pos_in_bank);
+
+	return BIT(bit_pos_in_bank);
 }
 
 #define PCA953x_BANK_INPUT	BIT(0)
···
 	return true;
 }
 
+/* TCA6418 breaks the PCA953x register order rule */
+static bool tca6418_check_register(struct pca953x_chip *chip, unsigned int reg,
+				   u32 access_type_mask)
+{
+	/*  Valid Input Registers - BIT(0) for readable access */
+	if (reg >= TCA6418_INPUT && reg < (TCA6418_INPUT + NBANK(chip)))
+		return (access_type_mask & BIT(0));
+
+	/*  Valid Output Registers - BIT(1) for writeable access */
+	if (reg >= TCA6418_OUTPUT && reg < (TCA6418_OUTPUT + NBANK(chip)))
+		return (access_type_mask & (BIT(0) | BIT(1)));
+
+	/*  Valid Direction Registers - BIT(2) for volatile access */
+	if (reg >= TCA6418_DIRECTION && reg < (TCA6418_DIRECTION + NBANK(chip)))
+		return (access_type_mask & (BIT(0) | BIT(1)));
+
+	return false;
+}
+
 static bool pca953x_readable_register(struct device *dev, unsigned int reg)
 {
 	struct pca953x_chip *chip = dev_get_drvdata(dev);
 	u32 bank;
 
-	if (PCA_CHIP_TYPE(chip->driver_data) == PCA957X_TYPE) {
+	switch (PCA_CHIP_TYPE(chip->driver_data)) {
+	case PCA957X_TYPE:
 		bank = PCA957x_BANK_INPUT | PCA957x_BANK_OUTPUT |
 		       PCA957x_BANK_POLARITY | PCA957x_BANK_CONFIG |
 		       PCA957x_BANK_BUSHOLD;
-	} else {
+		break;
+	case TCA6418_TYPE:
+		/* BIT(0) to indicate read access */
+		return tca6418_check_register(chip, reg, BIT(0));
+	default:
 		bank = PCA953x_BANK_INPUT | PCA953x_BANK_OUTPUT |
 		       PCA953x_BANK_POLARITY | PCA953x_BANK_CONFIG;
+		break;
 	}
 
 	if (chip->driver_data & PCA_PCAL) {
···
 	struct pca953x_chip *chip = dev_get_drvdata(dev);
 	u32 bank;
 
-	if (PCA_CHIP_TYPE(chip->driver_data) == PCA957X_TYPE) {
+	switch (PCA_CHIP_TYPE(chip->driver_data)) {
+	case PCA957X_TYPE:
 		bank = PCA957x_BANK_OUTPUT | PCA957x_BANK_POLARITY |
 			PCA957x_BANK_CONFIG | PCA957x_BANK_BUSHOLD;
-	} else {
+		break;
+	case TCA6418_TYPE:
+		/* BIT(1) for write access */
+		return tca6418_check_register(chip, reg, BIT(1));
+	default:
 		bank = PCA953x_BANK_OUTPUT | PCA953x_BANK_POLARITY |
 			PCA953x_BANK_CONFIG;
+		break;
 	}
 
 	if (chip->driver_data & PCA_PCAL)
···
 	struct pca953x_chip *chip = dev_get_drvdata(dev);
 	u32 bank;
 
-	if (PCA_CHIP_TYPE(chip->driver_data) == PCA957X_TYPE)
+	switch (PCA_CHIP_TYPE(chip->driver_data)) {
+	case PCA957X_TYPE:
 		bank = PCA957x_BANK_INPUT;
-	else
+		break;
+	case TCA6418_TYPE:
+		/* BIT(2) for volatile access */
+		return tca6418_check_register(chip, reg, BIT(2));
+	default:
 		bank = PCA953x_BANK_INPUT;
+		break;
+	}
 
 	if (chip->driver_data & PCA_PCAL)
 		bank |= PCAL9xxx_BANK_IRQ_STAT;
···
 	return pinctrl + addr + (off / BANK_SZ);
 }
 
+static u8 tca6418_recalc_addr(struct pca953x_chip *chip, int reg_base, int offset)
+{
+	/*
+	 * reg_base will be TCA6418_INPUT, TCA6418_OUTPUT, or TCA6418_DIRECTION
+	 * offset is the global GPIO line offset (0-17)
+	 * BANK_SZ is 8 for TCA6418 (8 bits per register bank)
+	 */
+	return reg_base + (offset / BANK_SZ);
+}
+
 static int pca953x_write_regs(struct pca953x_chip *chip, int reg, unsigned long *val)
 {
 	u8 regaddr = chip->recalc_addr(chip, reg, 0);
···
 {
 	struct pca953x_chip *chip = gpiochip_get_data(gc);
 	u8 dirreg = chip->recalc_addr(chip, chip->regs->direction, off);
-	u8 bit = BIT(off % BANK_SZ);
+	u8 bit = pca953x_get_bit_mask(chip, off);
 
 	guard(mutex)(&chip->i2c_lock);
+
+	if (PCA_CHIP_TYPE(chip->driver_data) == TCA6418_TYPE)
+		return regmap_write_bits(chip->regmap, dirreg, bit, 0);
 
 	return regmap_write_bits(chip->regmap, dirreg, bit, bit);
 }
···
 	struct pca953x_chip *chip = gpiochip_get_data(gc);
 	u8 dirreg = chip->recalc_addr(chip, chip->regs->direction, off);
 	u8 outreg = chip->recalc_addr(chip, chip->regs->output, off);
-	u8 bit = BIT(off % BANK_SZ);
+	u8 bit = pca953x_get_bit_mask(chip, off);
 	int ret;
 
 	guard(mutex)(&chip->i2c_lock);
···
 	if (ret)
 		return ret;
 
-	/* then direction */
+	/*
+	 * then direction
+	 * (in/out logic is inverted on TCA6418)
+	 */
+	if (PCA_CHIP_TYPE(chip->driver_data) == TCA6418_TYPE)
+		return regmap_write_bits(chip->regmap, dirreg, bit, bit);
+
 	return regmap_write_bits(chip->regmap, dirreg, bit, 0);
 }
 
···
 {
 	struct pca953x_chip *chip = gpiochip_get_data(gc);
 	u8 inreg = chip->recalc_addr(chip, chip->regs->input, off);
-	u8 bit = BIT(off % BANK_SZ);
+	u8 bit = pca953x_get_bit_mask(chip, off);
 	u32 reg_val;
 	int ret;
 
···
 {
 	struct pca953x_chip *chip = gpiochip_get_data(gc);
 	u8 outreg = chip->recalc_addr(chip, chip->regs->output, off);
-	u8 bit = BIT(off % BANK_SZ);
+	u8 bit = pca953x_get_bit_mask(chip, off);
 
 	guard(mutex)(&chip->i2c_lock);
 
···
 {
 	struct pca953x_chip *chip = gpiochip_get_data(gc);
 	u8 dirreg = chip->recalc_addr(chip, chip->regs->direction, off);
-	u8 bit = BIT(off % BANK_SZ);
+	u8 bit = pca953x_get_bit_mask(chip, off);
 	u32 reg_val;
 	int ret;
 
···
 	if (ret < 0)
 		return ret;
 
-	if (reg_val & bit)
+	/* (in/out logic is inverted on TCA6418) */
+	if (reg_val & bit) {
+		if (PCA_CHIP_TYPE(chip->driver_data) == TCA6418_TYPE)
+			return GPIO_LINE_DIRECTION_OUT;
+
+		return GPIO_LINE_DIRECTION_IN;
+	}
+	if (PCA_CHIP_TYPE(chip->driver_data) == TCA6418_TYPE)
 		return GPIO_LINE_DIRECTION_IN;
 
 	return GPIO_LINE_DIRECTION_OUT;
···
 		regmap_config = &pca953x_i2c_regmap;
 	}
 
-	if (PCA_CHIP_TYPE(chip->driver_data) == PCAL653X_TYPE) {
+	switch (PCA_CHIP_TYPE(chip->driver_data)) {
+	case PCAL653X_TYPE:
 		chip->recalc_addr = pcal6534_recalc_addr;
 		chip->check_reg = pcal6534_check_register;
-	} else {
+		break;
+	case TCA6418_TYPE:
+		chip->recalc_addr = tca6418_recalc_addr;
+		/*
+		 * We don't assign chip->check_reg = tca6418_check_register directly here.
+		 * Instead, the wrappers handle the dispatch based on PCA_CHIP_TYPE.
+		 */
+		break;
+	default:
 		chip->recalc_addr = pca953x_recalc_addr;
 		chip->check_reg = pca953x_check_register;
+		break;
 	}
 
 	chip->regmap = devm_regmap_init_i2c(client, regmap_config);
···
 	lockdep_set_subclass(&chip->i2c_lock,
 			     i2c_adapter_depth(client->adapter));
 
-	/* initialize cached registers from their original values.
+	/*
+	 * initialize cached registers from their original values.
 	 * we can't share this chip with another i2c master.
 	 */
-	if (PCA_CHIP_TYPE(chip->driver_data) == PCA957X_TYPE) {
+	switch (PCA_CHIP_TYPE(chip->driver_data)) {
+	case PCA957X_TYPE:
 		chip->regs = &pca957x_regs;
 		ret = device_pca957x_init(chip);
-	} else {
+		break;
+	case TCA6418_TYPE:
+		chip->regs = &tca6418_regs;
+		break;
+	default:
 		chip->regs = &pca953x_regs;
 		ret = device_pca95xx_init(chip);
+		break;
 	}
 	if (ret)
 		return ret;
···
 	{ .compatible = "ti,pca9536", .data = OF_953X( 4, 0), },
 	{ .compatible = "ti,tca6408", .data = OF_953X( 8, PCA_INT), },
 	{ .compatible = "ti,tca6416", .data = OF_953X(16, PCA_INT), },
+	{ .compatible = "ti,tca6418", .data = (void *)(18 | TCA6418_TYPE | PCA_INT), },
 	{ .compatible = "ti,tca6424", .data = OF_953X(24, PCA_INT), },
 	{ .compatible = "ti,tca9535", .data = OF_953X(16, PCA_INT), },
 	{ .compatible = "ti,tca9538", .data = OF_953X( 8, PCA_INT), },
···
 {
 	return i2c_add_driver(&pca953x_driver);
 }
-/* register after i2c postcore initcall and before
+
+/*
+ * register after i2c postcore initcall and before
  * subsys initcalls that may rely on these GPIOs
  */
 subsys_initcall(pca953x_init);