serial: sc16is7xx: hardware reset chip if reset-gpios is defined in DT

Some boards connect a GPIO to the reset pin, and the reset pin needs
to be set up correctly before accessing the chip.

Add a function to handle the chip reset. If the reset-gpios is defined
in the DT, do hardware reset through this GPIO, otherwise do software
reset as before.

Reviewed-by: Lech Perczak <[email protected]>
Tested-by: Hugo Villeneuve <[email protected]>
Reviewed-by: Hugo Villeneuve <[email protected]>
Signed-off-by: Hui Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index bf0065d1c8e9c3a85d8f2742023ebca17a6e72f8..c79dcd7c8d1a6032aed8ffc9bdaf7bd1623fd17a 100644 (file)
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -14,6 +14,7 @@
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/export.h>
+#include <linux/gpio/consumer.h>
 #include <linux/gpio/driver.h>
 #include <linux/idr.h>
 #include <linux/kthread.h>
@@ -1467,6 +1468,29 @@ static const struct serial_rs485 sc16is7xx_rs485_supported = {
        .delay_rts_after_send = 1,      /* Not supported but keep returning -EINVAL */
 };
 
+/* Reset device, purging any pending irq / data */
+static int sc16is7xx_reset(struct device *dev, struct regmap *regmap)
+{
+       struct gpio_desc *reset_gpio;
+
+       /* Assert reset GPIO if defined and valid. */
+       reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
+       if (IS_ERR(reset_gpio))
+               return dev_err_probe(dev, PTR_ERR(reset_gpio), "Failed to get reset GPIO\n");
+
+       if (reset_gpio) {
+               /* The minimum reset pulse width is 3 us. */
+               fsleep(5);
+               gpiod_set_value_cansleep(reset_gpio, 0); /* Deassert GPIO */
+       } else {
+               /* Software reset */
+               regmap_write(regmap, SC16IS7XX_IOCONTROL_REG,
+                            SC16IS7XX_IOCONTROL_SRESET_BIT);
+       }
+
+       return 0;
+}
+
 int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
                    struct regmap *regmaps[], int irq)
 {
@@ -1536,9 +1560,9 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
        }
        sched_set_fifo(s->kworker_task);
 
-       /* reset device, purging any pending irq / data */
-       regmap_write(regmaps[0], SC16IS7XX_IOCONTROL_REG,
-                    SC16IS7XX_IOCONTROL_SRESET_BIT);
+       ret = sc16is7xx_reset(dev, regmaps[0]);
+       if (ret)
+               goto out_kthread;
 
        /* Mark each port line and status as uninitialised. */
        for (i = 0; i < devtype->nr_uart; ++i) {
@@ -1663,6 +1687,7 @@ out_ports:
                        uart_remove_one_port(&sc16is7xx_uart, &s->p[i].port);
        }
 
+out_kthread:
        kthread_stop(s->kworker_task);
 
 out_clk: