[PATCH v3 3/3] serial: sc16is7xx: add support for EXAR XR20M1172 UART

Konstantin Pugin
2024-04-18T17:12:22Z

From: Konstantin Pugin <ria.freelander@gmail.com>

XR20M1172 register set is mostly compatible with SC16IS762, but it has
a support for additional division rates of UART with special DLD register.
So, add handling this register by appropriate devicetree bindings.

Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Konstantin Pugin <ria.freelander@gmail.com>
---
drivers/tty/serial/sc16is7xx.c | 55 +++++++++++++++++++++++++++++++---
1 file changed, 51 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index a300eebf1401..59376c637467 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -65,6 +65,7 @@
/* Special Register set: Only if ((LCR[7] == 1) && (LCR != 0xBF)) */
#define SC16IS7XX_DLL_REG (0x00) /* Divisor Latch Low */
#define SC16IS7XX_DLH_REG (0x01) /* Divisor Latch High */
+#define XR20M117X_DLD_REG (0x02) /* Divisor Fractional Register (only on EXAR chips) */

/* Enhanced Register set: Only if (LCR == 0xBF) */
#define SC16IS7XX_EFR_REG (0x02) /* Enhanced Features */
@@ -218,6 +219,20 @@
#define SC16IS7XX_TCR_RX_HALT(words) ((((words) / 4) & 0x0f) << 0)
#define SC16IS7XX_TCR_RX_RESUME(words) ((((words) / 4) & 0x0f) << 4)

+/*
+ * Divisor Fractional Register bits (EXAR extension)
+ * EXAR hardware is mostly compatible with SC16IS7XX, but supports additional feature:
+ * 4x and 8x divisor, instead of default 16x. It has a special register to program it.
+ * Bits 0 to 3 is fractional divisor, it used to set value of last 16 bits of
+ * uartclk * (16 / divisor) / baud, in case of default it will be uartclk / baud.
+ * Bits 4 and 5 used as switches, and should not be set to 1 simultaneously.
+ */
+
+#define XR20M117X_DLD_16X 0
+#define XR20M117X_DLD_DIV(m) ((m) & GENMASK(3, 0))
+#define XR20M117X_DLD_8X BIT(4)
+#define XR20M117X_DLD_4X BIT(5)
+
/*
* TLR register bits
* If TLR[3:0] or TLR[7:4] are logical 0, the selectable trigger levels via the
@@ -310,6 +325,7 @@ struct sc16is7xx_devtype {
char name[10];
int nr_gpio;
int nr_uart;
+ bool has_dld;
};

#define SC16IS7XX_RECONF_MD (1 << 0)
@@ -522,6 +538,13 @@ static const struct sc16is7xx_devtype sc16is762_devtype = {
.nr_uart = 2,
};

+static const struct sc16is7xx_devtype xr20m1172_devtype = {
+ .name = "XR20M1172",
+ .nr_gpio = 8,
+ .nr_uart = 2,
+ .has_dld = true,
+};
+
static bool sc16is7xx_regmap_volatile(struct device *dev, unsigned int reg)
{
switch (reg) {
@@ -556,16 +579,33 @@ static bool sc16is7xx_regmap_noinc(struct device *dev, unsigned int reg)

static int sc16is7xx_set_baud(struct uart_port *port, int baud)
{
+ struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
- u8 lcr;
+ unsigned long clk = port->uartclk, div, div16;
+ bool has_dld = s->devtype->has_dld;
+ u8 dld_mode = XR20M117X_DLD_16X;
u8 prescaler = 0;
- unsigned long clk = port->uartclk, div = clk / 16 / baud;
+ u8 divisor = 16;
+ u8 lcr;
+
+ if (has_dld && DIV_ROUND_CLOSEST(clk, baud) < 16)
+ divisor = 1 << (fls(DIV_ROUND_CLOSEST(clk, baud)) - 1);
+
+ div16 = (clk * 16) / divisor / baud;
+ div = div16 / 16;

if (div >= BIT(16)) {
prescaler = SC16IS7XX_MCR_CLKSEL_BIT;
div /= 4;
}

+ /* Count additional divisor for EXAR devices */
+ if (divisor == 8)
+ dld_mode = XR20M117X_DLD_8X;
+ if (divisor == 4)
+ dld_mode = XR20M117X_DLD_4X;
+ dld_mode |= XR20M117X_DLD_DIV(div16);
+
/* Enable enhanced features */
sc16is7xx_efr_lock(port);
sc16is7xx_port_update(port, SC16IS7XX_EFR_REG,
@@ -586,12 +626,14 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
regcache_cache_bypass(one->regmap, true);
sc16is7xx_port_write(port, SC16IS7XX_DLH_REG, div / 256);
sc16is7xx_port_write(port, SC16IS7XX_DLL_REG, div % 256);
+ if (has_dld)
+ sc16is7xx_port_write(port, XR20M117X_DLD_REG, dld_mode);
regcache_cache_bypass(one->regmap, false);

/* Restore LCR and access to general register set */
sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);

- return DIV_ROUND_CLOSEST(clk / 16, div);
+ return DIV_ROUND_CLOSEST(clk / divisor, div);
}

static void sc16is7xx_handle_rx(struct uart_port *port, unsigned int rxlen,
@@ -1010,7 +1052,9 @@ static void sc16is7xx_set_termios(struct uart_port *port,
struct ktermios *termios,
const struct ktermios *old)
{
+ struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
+ bool has_dld = s->devtype->has_dld;
unsigned int lcr, flow = 0;
int baud;
unsigned long flags;
@@ -1093,7 +1137,7 @@ static void sc16is7xx_set_termios(struct uart_port *port,
/* Get baud rate generator configuration */
baud = uart_get_baud_rate(port, termios, old,
port->uartclk / 16 / 4 / 0xffff,
- port->uartclk / 16);
+ port->uartclk / (has_dld ? 4 : 16));

/* Setup baudrate generator */
baud = sc16is7xx_set_baud(port, baud);
@@ -1682,6 +1726,7 @@ static void sc16is7xx_remove(struct device *dev)
}

static const struct of_device_id __maybe_unused sc16is7xx_dt_ids[] = {
+ { .compatible = "exar,xr20m1172", .data = &xr20m1172_devtype, },
{ .compatible = "nxp,sc16is740", .data = &sc16is74x_devtype, },
{ .compatible = "nxp,sc16is741", .data = &sc16is74x_devtype, },
{ .compatible = "nxp,sc16is750", .data = &sc16is750_devtype, },
@@ -1776,6 +1821,7 @@ static const struct spi_device_id sc16is7xx_spi_id_table[] = {
{ "sc16is752", (kernel_ulong_t)&sc16is752_devtype, },
{ "sc16is760", (kernel_ulong_t)&sc16is760_devtype, },
{ "sc16is762", (kernel_ulong_t)&sc16is762_devtype, },
+ { "xr20m1172", (kernel_ulong_t)&xr20m1172_devtype, },
{ }
};

@@ -1826,6 +1872,7 @@ static const struct i2c_device_id sc16is7xx_i2c_id_table[] = {
{ "sc16is752", (kernel_ulong_t)&sc16is752_devtype, },
{ "sc16is760", (kernel_ulong_t)&sc16is760_devtype, },
{ "sc16is762", (kernel_ulong_t)&sc16is762_devtype, },
+ { "xr20m1172", (kernel_ulong_t)&xr20m1172_devtype, },
{ }
};
MODULE_DEVICE_TABLE(i2c, sc16is7xx_i2c_id_table);
--
2.34.1