The Synopsys DesignWare UART can be configured to have HW support for
the RS485 protocol from IP version 4.0 onward. Add support for
hardware-controlled half duplex and full duplex modes.
HW will take care of managing DE and RE, the driver just gives it
permission to use either by setting both to 1.
To ask for full duplex mode, userspace sets SER_RS485_RX_DURING_TX flag
and HW will take care of the rest.
Set delay_rts_before_send and delay_rts_after_send to zero for now. The
granularity of that ABI is too coarse to be useful.
Co-developed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
Signed-off-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
Co-developed-by: Raymond Tan <raymond.tan@xxxxxxxxx>
Signed-off-by: Raymond Tan <raymond.tan@xxxxxxxxx>
Co-developed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250_dwlib.c | 85 +++++++++++++++++++++++++++-
drivers/tty/serial/8250/8250_dwlib.h | 3 +
2 files changed, 86 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_dwlib.c b/drivers/tty/serial/8250/8250_dwlib.c
index 622d3b0d89e7..08432e2fe511 100644
--- a/drivers/tty/serial/8250/8250_dwlib.c
+++ b/drivers/tty/serial/8250/8250_dwlib.c
@@ -2,19 +2,33 @@
/* Synopsys DesignWare 8250 library. */
#include <linux/bitops.h>
+#include <linux/bitfield.h>
#include <linux/device.h>
#include <linux/io.h>
#include <linux/kernel.h>
+#include <linux/property.h>
#include <linux/serial_8250.h>
#include <linux/serial_core.h>
#include "8250_dwlib.h"
/* Offsets for the DesignWare specific registers */
+#define DW_UART_TCR 0xac /* Transceiver Control Register (RS485) */
+#define DW_UART_DE_EN 0xb0 /* Driver Output Enable Register */
+#define DW_UART_RE_EN 0xb4 /* Receiver Output Enable Register */
#define DW_UART_DLF 0xc0 /* Divisor Latch Fraction Register */
#define DW_UART_CPR 0xf4 /* Component Parameter Register */
#define DW_UART_UCV 0xf8 /* UART Component Version */
+/* Transceiver Control Register bits */
+#define DW_UART_TCR_RS485_EN BIT(0)
+#define DW_UART_TCR_RE_POL BIT(1)
+#define DW_UART_TCR_DE_POL BIT(2)
+#define DW_UART_TCR_XFER_MODE GENMASK(4, 3)
+#define DW_UART_TCR_XFER_MODE_DE_DURING_RE FIELD_PREP(DW_UART_TCR_XFER_MODE, 0)
+#define DW_UART_TCR_XFER_MODE_SW_DE_OR_RE FIELD_PREP(DW_UART_TCR_XFER_MODE, 1)
+#define DW_UART_TCR_XFER_MODE_DE_OR_RE FIELD_PREP(DW_UART_TCR_XFER_MODE, 2)
+
/* Component Parameter Register bits */
#define DW_UART_CPR_ABP_DATA_WIDTH (3 << 0)
#define DW_UART_CPR_AFCE_MODE (1 << 4)
@@ -87,11 +101,80 @@ void dw8250_do_set_termios(struct uart_port *p, struct ktermios *termios, struct
}
EXPORT_SYMBOL_GPL(dw8250_do_set_termios);
+static int dw8250_rs485_config(struct uart_port *p, struct serial_rs485 *rs485)
+{
+ u32 tcr;
+
+ tcr = dw8250_readl_ext(p, DW_UART_TCR);
+ tcr &= ~DW_UART_TCR_XFER_MODE;
+
+ if (rs485->flags & SER_RS485_ENABLED) {
+ /* Clear unsupported flags. */
+ rs485->flags &= SER_RS485_ENABLED | SER_RS485_RX_DURING_TX |
+ SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND;
+ tcr |= DW_UART_TCR_RS485_EN;
+
+ if (rs485->flags & SER_RS485_RX_DURING_TX) {
+ tcr |= DW_UART_TCR_XFER_MODE_DE_DURING_RE;
+ } else {
+ /* HW does not support same DE level for tx and rx */
+ if (!(rs485->flags & SER_RS485_RTS_ON_SEND) ==
+ !(rs485->flags & SER_RS485_RTS_AFTER_SEND))
+ return -EINVAL;
+
+ tcr |= DW_UART_TCR_XFER_MODE_DE_OR_RE;
+ }
+ dw8250_writel_ext(p, DW_UART_DE_EN, 1);
+ dw8250_writel_ext(p, DW_UART_RE_EN, 1);
+ } else {
+ rs485->flags = 0;
+
+ tcr &= ~DW_UART_TCR_RS485_EN;
+ }
+
+ /* Reset to default polarity */
+ tcr |= DW_UART_TCR_DE_POL;
+ tcr &= ~DW_UART_TCR_RE_POL;
+
+ if (!(rs485->flags & SER_RS485_RTS_ON_SEND))
+ tcr &= ~DW_UART_TCR_DE_POL;
+ if (device_property_read_bool(p->dev, "rs485-rx-active-high"))
+ tcr |= DW_UART_TCR_RE_POL;
+
+ dw8250_writel_ext(p, DW_UART_TCR, tcr);
+
+ rs485->delay_rts_before_send = 0;
+ rs485->delay_rts_after_send = 0;
+
+ p->rs485 = *rs485;
+
+ return 0;
+}
+
+/*
+ * Tests if RE_EN register can have non-zero value to see if RS-485 HW support
+ * is present.
+ */
+static bool dw8250_detect_rs485_hw(struct uart_port *p)
+{
+ u32 reg;
+
+ dw8250_writel_ext(p, DW_UART_RE_EN, 1);
+ reg = dw8250_readl_ext(p, DW_UART_RE_EN);
+ dw8250_writel_ext(p, DW_UART_RE_EN, 0);
+ return reg;
+}
+
void dw8250_setup_port(struct uart_port *p)
{
+ struct dw8250_port_data *d = p->private_data;
struct uart_8250_port *up = up_to_u8250p(p);
u32 reg;
+ d->hw_rs485_support = dw8250_detect_rs485_hw(p);
+ if (d->hw_rs485_support)
+ p->rs485_config = dw8250_rs485_config;
+
/*
* If the Component Version Register returns zero, we know that
* ADDITIONAL_FEATURES are not enabled. No need to go any further.
@@ -108,8 +191,6 @@ void dw8250_setup_port(struct uart_port *p)
dw8250_writel_ext(p, DW_UART_DLF, 0);
if (reg) {
- struct dw8250_port_data *d = p->private_data;
-
d->dlf_size = fls(reg);
p->get_divisor = dw8250_get_divisor;
p->set_divisor = dw8250_set_divisor;
diff --git a/drivers/tty/serial/8250/8250_dwlib.h b/drivers/tty/serial/8250/8250_dwlib.h
index 83d528e5cc21..a8fa020ca544 100644
--- a/drivers/tty/serial/8250/8250_dwlib.h
+++ b/drivers/tty/serial/8250/8250_dwlib.h
@@ -14,6 +14,9 @@ struct dw8250_port_data {
/* Hardware configuration */
u8 dlf_size;
+
+ /* RS485 variables */
+ bool hw_rs485_support;
};
void dw8250_do_set_termios(struct uart_port *p, struct ktermios *termios, struct ktermios *old);
--
2.30.2
