[PATCH v7 6/6] serial: 8250_dwlib: Support for 9th bit multipoint addressing

Ilpo Järvinen
2022-06-15T12:49:31Z

Add 9th bit multipoint addressing mode for DW UART. 9th bit addressing
can be used only when HW RS485 is available.

Updating RAR (receive address register) is bit tricky because busy
indication is not be available when DW UART is strictly 16550
compatible, which is the case with the hardware I was testing with. RAR
should not be updated while receive is in progress which is now
achieved by deasserting RE and waiting for one frame (in case rx would
be in progress, the driver seems to have no way of knowing it w/o busy
indication). Because of this complexity, it's better to avoid doing it
unless really needed.

Co-developed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Co-developed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Co-developed-by: Raymond Tan <raymond.tan@intel.com>
Signed-off-by: Raymond Tan <raymond.tan@intel.com>
Co-developed-by: Lakshmi Sowjanya <lakshmi.sowjanya.d@intel.com>
Signed-off-by: Lakshmi Sowjanya <lakshmi.sowjanya.d@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/tty/serial/8250/8250_dwlib.c | 102 ++++++++++++++++++++++++++-
1 file changed, 101 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_dwlib.c b/drivers/tty/serial/8250/8250_dwlib.c
index c9d9bd7f7bd9..fe6feb59e68d 100644
--- a/drivers/tty/serial/8250/8250_dwlib.c
+++ b/drivers/tty/serial/8250/8250_dwlib.c
@@ -3,8 +3,10 @@

#include <linux/bitops.h>
#include <linux/bitfield.h>
+#include <linux/delay.h>
#include <linux/device.h>
#include <linux/kernel.h>
+#include <linux/math.h>
#include <linux/property.h>
#include <linux/serial_8250.h>
#include <linux/serial_core.h>
@@ -16,9 +18,18 @@
#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_RAR 0xc4 /* Receive Address Register */
+#define DW_UART_TAR 0xc8 /* Transmit Address Register */
+#define DW_UART_LCR_EXT 0xcc /* Line Extended Control Register */
#define DW_UART_CPR 0xf4 /* Component Parameter Register */
#define DW_UART_UCV 0xf8 /* UART Component Version */

+/* Receive / Transmit Address Register bits */
+#define DW_UART_ADDR_MASK GENMASK(7, 0)
+
+/* Line Status Register bits */
+#define DW_UART_LSR_ADDR_RCVD BIT(8)
+
/* Transceiver Control Register bits */
#define DW_UART_TCR_RS485_EN BIT(0)
#define DW_UART_TCR_RE_POL BIT(1)
@@ -28,6 +39,12 @@
#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)

+/* Line Extended Control Register bits */
+#define DW_UART_LCR_EXT_DLS_E BIT(0)
+#define DW_UART_LCR_EXT_ADDR_MATCH BIT(1)
+#define DW_UART_LCR_EXT_SEND_ADDR BIT(2)
+#define DW_UART_LCR_EXT_TRANSMIT_MODE BIT(3)
+
/* Component Parameter Register bits */
#define DW_UART_CPR_ABP_DATA_WIDTH (3 << 0)
#define DW_UART_CPR_AFCE_MODE (1 << 4)
@@ -82,9 +99,83 @@ void dw8250_do_set_termios(struct uart_port *p, struct ktermios *termios, struct
p->status |= UPSTAT_AUTOCTS;

serial8250_do_set_termios(p, termios, old);
+
+ /* Filter addresses which have 9th bit set */
+ p->ignore_status_mask |= DW_UART_LSR_ADDR_RCVD;
+ p->read_status_mask |= DW_UART_LSR_ADDR_RCVD;
}
EXPORT_SYMBOL_GPL(dw8250_do_set_termios);

+/*
+ * Wait until re is de-asserted for sure. An ongoing receive will keep
+ * re asserted until end of frame. Without BUSY indication available,
+ * only available course of action is to wait for the time it takes to
+ * receive one frame (there might nothing to receive but w/o BUSY the
+ * driver cannot know).
+ */
+static void dw8250_wait_re_deassert(struct uart_port *p)
+{
+ ndelay(p->frame_time);
+}
+
+static void dw8250_update_rar(struct uart_port *p, u32 addr)
+{
+ u32 re_en = dw8250_readl_ext(p, DW_UART_RE_EN);
+
+ /*
+ * RAR shouldn't be changed while receiving. Thus, de-assert RE_EN
+ * if asserted and wait.
+ */
+ if (re_en)
+ dw8250_writel_ext(p, DW_UART_RE_EN, 0);
+ dw8250_wait_re_deassert(p);
+ dw8250_writel_ext(p, DW_UART_RAR, addr);
+ if (re_en)
+ dw8250_writel_ext(p, DW_UART_RE_EN, re_en);
+}
+
+static void dw8250_rs485_set_addr(struct uart_port *p, struct serial_rs485 *rs485,
+ struct ktermios *termios)
+{
+ u32 lcr = dw8250_readl_ext(p, DW_UART_LCR_EXT);
+
+ if (rs485->flags & SER_RS485_ADDRB) {
+ lcr |= DW_UART_LCR_EXT_DLS_E;
+ if (termios)
+ termios->c_cflag |= ADDRB;
+
+ if (rs485->flags & SER_RS485_ADDR_RECV) {
+ u32 delta = p->rs485.flags ^ rs485->flags;
+
+ /*
+ * rs485 (param) is equal to uart_port's rs485 only during init
+ * (during init, delta is not yet applicable).
+ */
+ if (unlikely(&p->rs485 == rs485))
+ delta = rs485->flags;
+
+ if ((delta & SER_RS485_ADDR_RECV) ||
+ (p->rs485.addr_recv != rs485->addr_recv))
+ dw8250_update_rar(p, rs485->addr_recv);
+ lcr |= DW_UART_LCR_EXT_ADDR_MATCH;
+ } else {
+ lcr &= ~DW_UART_LCR_EXT_ADDR_MATCH;
+ }
+ if (rs485->flags & SER_RS485_ADDR_DEST) {
+ /*
+ * Don't skip writes here as another endpoint could
+ * have changed communication line's destination
+ * address in between.
+ */
+ dw8250_writel_ext(p, DW_UART_TAR, rs485->addr_dest);
+ lcr |= DW_UART_LCR_EXT_SEND_ADDR;
+ }
+ } else {
+ lcr = 0;
+ }
+ dw8250_writel_ext(p, DW_UART_LCR_EXT, lcr);
+}
+
static int dw8250_rs485_config(struct uart_port *p, struct serial_rs485 *rs485,
struct ktermios *termios)
{
@@ -109,6 +200,9 @@ static int dw8250_rs485_config(struct uart_port *p, struct serial_rs485 *rs485,
dw8250_writel_ext(p, DW_UART_DE_EN, 1);
dw8250_writel_ext(p, DW_UART_RE_EN, 1);
} else {
+ if (termios)
+ termios->c_cflag &= ~ADDRB;
+
tcr &= ~DW_UART_TCR_RS485_EN;
}

@@ -123,6 +217,10 @@ static int dw8250_rs485_config(struct uart_port *p, struct serial_rs485 *rs485,

dw8250_writel_ext(p, DW_UART_TCR, tcr);

+ /* Addressing mode can only be set up after TCR */
+ if (rs485->flags & SER_RS485_ENABLED)
+ dw8250_rs485_set_addr(p, rs485, termios);
+
return 0;
}

@@ -142,7 +240,8 @@ static bool dw8250_detect_rs485_hw(struct uart_port *p)

static const struct serial_rs485 dw8250_rs485_supported = {
.flags = SER_RS485_ENABLED | SER_RS485_RX_DURING_TX | SER_RS485_RTS_ON_SEND |
- SER_RS485_RTS_AFTER_SEND,
+ SER_RS485_RTS_AFTER_SEND | SER_RS485_ADDRB | SER_RS485_ADDR_RECV |
+ SER_RS485_ADDR_DEST,
};

void dw8250_setup_port(struct uart_port *p)
@@ -155,6 +254,7 @@ void dw8250_setup_port(struct uart_port *p)
pd->hw_rs485_support = dw8250_detect_rs485_hw(p);
if (pd->hw_rs485_support) {
p->rs485_config = dw8250_rs485_config;
+ up->lsr_save_mask = LSR_SAVE_FLAGS | DW_UART_LSR_ADDR_RCVD;
p->rs485_supported = &dw8250_rs485_supported;
} else {
p->rs485_config = serial8250_em485_config;
--
2.30.2