[PATCH v2 3/4] serial: max310x: make accessing revision id interface-agnostic

[Cosmin Tanislav <demonsingur@gmail.com>]

From: Cosmin Tanislav <cosmin.tanislav@analog.com>

SPI can only use 5 address bits, since one bit is reserved for
specifying R/W and 2 bits are used to specify the UART port.
To access registers that have addresses past 0x1F, an extended
register space can be enabled by writing to the GlobalCommand
register (address 0x1F).

I2C uses 8 address bits. The R/W bit is placed in the slave
address, and so is the UART port. Because of this, registers
that have addresses higher than 0x1F can be accessed normally.

To access the RevID register, on SPI, 0xCE must be written to
the 0x1F address to enable the extended register space, after
which the RevID register is accessible at address 0x5. 0xCD
must be written to the 0x1F address to disable the extended
register space.

On I2C, the RevID register is accessible at address 0x25.

Create an interface config struct, and add a method for
toggling the extended register space and a member for the RevId
register address. Implement these for SPI.

Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
---
 drivers/tty/serial/max310x.c | 40 +++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index 6fd133c177a3..ef6b91242524 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -72,7 +72,7 @@
 #define MAX310X_GLOBALCMD_REG		MAX310X_REG_1F /* Global Command (WO) */
 
 /* Extended registers */
-#define MAX310X_REVID_EXTREG		MAX310X_REG_05 /* Revision ID */
+#define MAX310X_SPI_REVID_EXTREG	MAX310X_REG_05 /* Revision ID */
 
 /* IRQ register bits */
 #define MAX310X_IRQ_LSR_BIT		(1 << 0) /* LSR interrupt */
@@ -245,6 +245,12 @@
 #define MAX14830_BRGCFG_CLKDIS_BIT	(1 << 6) /* Clock Disable */
 #define MAX14830_REV_ID			(0xb0)
 
+struct max310x_if_cfg {
+	int (*extended_reg_enable)(struct device *dev, bool enable);
+
+	unsigned int rev_id_reg;
+};
+
 struct max310x_devtype {
 	char	name[9];
 	int	nr;
@@ -267,6 +273,7 @@ struct max310x_one {
 
 struct max310x_port {
 	const struct max310x_devtype *devtype;
+	const struct max310x_if_cfg *if_cfg;
 	struct regmap		*regmap;
 	struct clk		*clk;
 #ifdef CONFIG_GPIOLIB
@@ -356,13 +363,12 @@ static int max3109_detect(struct device *dev)
 	unsigned int val = 0;
 	int ret;
 
-	ret = regmap_write(s->regmap, MAX310X_GLOBALCMD_REG,
-			   MAX310X_EXTREG_ENBL);
+	ret = s->if_cfg->extended_reg_enable(dev, true);
 	if (ret)
 		return ret;
 
-	regmap_read(s->regmap, MAX310X_REVID_EXTREG, &val);
-	regmap_write(s->regmap, MAX310X_GLOBALCMD_REG, MAX310X_EXTREG_DSBL);
+	regmap_read(s->regmap, s->if_cfg->rev_id_reg, &val);
+	s->if_cfg->extended_reg_enable(dev, false);
 	if (((val & MAX310x_REV_MASK) != MAX3109_REV_ID)) {
 		dev_err(dev,
 			"%s ID 0x%02x does not match\n", s->devtype->name, val);
@@ -387,13 +393,12 @@ static int max14830_detect(struct device *dev)
 	unsigned int val = 0;
 	int ret;
 
-	ret = regmap_write(s->regmap, MAX310X_GLOBALCMD_REG,
-			   MAX310X_EXTREG_ENBL);
+	ret = s->if_cfg->extended_reg_enable(dev, true);
 	if (ret)
 		return ret;
 	
-	regmap_read(s->regmap, MAX310X_REVID_EXTREG, &val);
-	regmap_write(s->regmap, MAX310X_GLOBALCMD_REG, MAX310X_EXTREG_DSBL);
+	regmap_read(s->regmap, s->if_cfg->rev_id_reg, &val);
+	s->if_cfg->extended_reg_enable(dev, false);
 	if (((val & MAX310x_REV_MASK) != MAX14830_REV_ID)) {
 		dev_err(dev,
 			"%s ID 0x%02x does not match\n", s->devtype->name, val);
@@ -1233,6 +1238,7 @@ static int max310x_gpio_set_config(struct gpio_chip *chip, unsigned int offset,
 #endif
 
 static int max310x_probe(struct device *dev, const struct max310x_devtype *devtype,
+			 const struct max310x_if_cfg *if_cfg,
 			 struct regmap *regmaps[], int irq)
 {
 	int i, ret, fmin, fmax, freq;
@@ -1291,6 +1297,7 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 
 	s->regmap = regmaps[0];
 	s->devtype = devtype;
+	s->if_cfg = if_cfg;
 	dev_set_drvdata(dev, s);
 
 	/* Check device to ensure we are talking to what we expect */
@@ -1441,6 +1448,19 @@ static struct regmap_config regcfg = {
 };
 
 #ifdef CONFIG_SPI_MASTER
+static int max310x_spi_extended_reg_enable(struct device *dev, bool enable)
+{
+	struct max310x_port *s = dev_get_drvdata(dev);
+
+	return regmap_write(s->regmap, MAX310X_GLOBALCMD_REG,
+			    enable ? MAX310X_EXTREG_ENBL : MAX310X_EXTREG_DSBL);
+}
+
+static const struct max310x_if_cfg __maybe_unused max310x_spi_if_cfg = {
+	.extended_reg_enable = max310x_spi_extended_reg_enable,
+	.rev_id_reg = MAX310X_SPI_REVID_EXTREG,
+};
+
 static int max310x_spi_probe(struct spi_device *spi)
 {
 	const struct max310x_devtype *devtype;
@@ -1467,7 +1487,7 @@ static int max310x_spi_probe(struct spi_device *spi)
 		regmaps[i] = devm_regmap_init_spi(spi, &regcfg);
 	}
 
-	return max310x_probe(&spi->dev, devtype, regmaps, spi->irq);
+	return max310x_probe(&spi->dev, devtype, &max310x_spi_if_cfg, regmaps, spi->irq);
 }
 
 static void max310x_spi_remove(struct spi_device *spi)
-- 
2.36.1