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serial: amba-pl011: add RS485 support
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Add basic support for RS485: Provide a callback to configure RS485
settings. Handle the RS485 specific part in the functions
pl011_rs485_tx_start() and pl011_rs485_tx_stop() which extend the generic
start/stop callbacks.
Beside via IOCTL from userspace RS485 can be enabled by means of the
device tree property "rs485-enabled-at-boot-time".

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Link: https://lore.kernel.org/r/20210630225644.3744-1-LinoSanfilippo@gmx.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Lino Sanfilippo authored and Greg Kroah-Hartman committed Jul 21, 2021
1 parent 240e126 commit 8d47923
Showing 1 changed file with 161 additions and 2 deletions.
163 changes: 161 additions & 2 deletions drivers/tty/serial/amba-pl011.c
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Original file line number Diff line number Diff line change
Expand Up @@ -265,6 +265,8 @@ struct uart_amba_port {
unsigned int old_cr; /* state during shutdown */
unsigned int fixed_baud; /* vendor-set fixed baud rate */
char type[12];
bool rs485_tx_started;
unsigned int rs485_tx_drain_interval; /* usecs */
#ifdef CONFIG_DMA_ENGINE
/* DMA stuff */
bool using_tx_dma;
Expand All @@ -275,6 +277,8 @@ struct uart_amba_port {
#endif
};

static unsigned int pl011_tx_empty(struct uart_port *port);

static unsigned int pl011_reg_to_offset(const struct uart_amba_port *uap,
unsigned int reg)
{
Expand Down Expand Up @@ -1282,6 +1286,42 @@ static inline bool pl011_dma_rx_running(struct uart_amba_port *uap)
#define pl011_dma_flush_buffer NULL
#endif

static void pl011_rs485_tx_stop(struct uart_amba_port *uap)
{
struct uart_port *port = &uap->port;
int i = 0;
u32 cr;

/* Wait until hardware tx queue is empty */
while (!pl011_tx_empty(port)) {
if (i == port->fifosize) {
dev_warn(port->dev,
"timeout while draining hardware tx queue\n");
break;
}

udelay(uap->rs485_tx_drain_interval);
i++;
}

if (port->rs485.delay_rts_after_send)
mdelay(port->rs485.delay_rts_after_send);

cr = pl011_read(uap, REG_CR);

if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
cr &= ~UART011_CR_RTS;
else
cr |= UART011_CR_RTS;

/* Disable the transmitter and reenable the transceiver */
cr &= ~UART011_CR_TXE;
cr |= UART011_CR_RXE;
pl011_write(cr, uap, REG_CR);

uap->rs485_tx_started = false;
}

static void pl011_stop_tx(struct uart_port *port)
{
struct uart_amba_port *uap =
Expand All @@ -1290,6 +1330,9 @@ static void pl011_stop_tx(struct uart_port *port)
uap->im &= ~UART011_TXIM;
pl011_write(uap->im, uap, REG_IMSC);
pl011_dma_tx_stop(uap);

if ((port->rs485.flags & SER_RS485_ENABLED) && uap->rs485_tx_started)
pl011_rs485_tx_stop(uap);
}

static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq);
Expand Down Expand Up @@ -1380,6 +1423,32 @@ static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c,
return true;
}

static void pl011_rs485_tx_start(struct uart_amba_port *uap)
{
struct uart_port *port = &uap->port;
u32 cr;

/* Enable transmitter */
cr = pl011_read(uap, REG_CR);
cr |= UART011_CR_TXE;

/* Disable receiver if half-duplex */
if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
cr &= ~UART011_CR_RXE;

if (port->rs485.flags & SER_RS485_RTS_ON_SEND)
cr &= ~UART011_CR_RTS;
else
cr |= UART011_CR_RTS;

pl011_write(cr, uap, REG_CR);

if (port->rs485.delay_rts_before_send)
mdelay(port->rs485.delay_rts_before_send);

uap->rs485_tx_started = true;
}

/* Returns true if tx interrupts have to be (kept) enabled */
static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
{
Expand All @@ -1397,6 +1466,10 @@ static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
return false;
}

if ((uap->port.rs485.flags & SER_RS485_ENABLED) &&
!uap->rs485_tx_started)
pl011_rs485_tx_start(uap);

/* If we are using DMA mode, try to send some characters. */
if (pl011_dma_tx_irq(uap))
return true;
Expand Down Expand Up @@ -1542,6 +1615,9 @@ static void pl011_set_mctrl(struct uart_port *port, unsigned int mctrl)
container_of(port, struct uart_amba_port, port);
unsigned int cr;

if (port->rs485.flags & SER_RS485_ENABLED)
mctrl &= ~TIOCM_RTS;

cr = pl011_read(uap, REG_CR);

#define TIOCMBIT(tiocmbit, uartbit) \
Expand Down Expand Up @@ -1763,7 +1839,17 @@ static int pl011_startup(struct uart_port *port)

/* restore RTS and DTR */
cr = uap->old_cr & (UART011_CR_RTS | UART011_CR_DTR);
cr |= UART01x_CR_UARTEN | UART011_CR_RXE | UART011_CR_TXE;
cr |= UART01x_CR_UARTEN | UART011_CR_RXE;

if (port->rs485.flags & SER_RS485_ENABLED) {
if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
cr &= ~UART011_CR_RTS;
else
cr |= UART011_CR_RTS;
} else {
cr |= UART011_CR_TXE;
}

pl011_write(cr, uap, REG_CR);

spin_unlock_irq(&uap->port.lock);
Expand Down Expand Up @@ -1864,6 +1950,9 @@ static void pl011_shutdown(struct uart_port *port)

pl011_dma_shutdown(uap);

if ((port->rs485.flags & SER_RS485_ENABLED) && uap->rs485_tx_started)
pl011_rs485_tx_stop(uap);

free_irq(uap->port.irq, uap);

pl011_disable_uart(uap);
Expand Down Expand Up @@ -1941,6 +2030,7 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
unsigned int lcr_h, old_cr;
unsigned long flags;
unsigned int baud, quot, clkdiv;
unsigned int bits;

if (uap->vendor->oversampling)
clkdiv = 8;
Expand Down Expand Up @@ -1991,18 +2081,30 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
if (uap->fifosize > 1)
lcr_h |= UART01x_LCRH_FEN;

bits = tty_get_frame_size(termios->c_cflag);

spin_lock_irqsave(&port->lock, flags);

/*
* Update the per-port timeout.
*/
uart_update_timeout(port, termios->c_cflag, baud);

/*
* Calculate the approximated time it takes to transmit one character
* with the given baud rate. We use this as the poll interval when we
* wait for the tx queue to empty.
*/
uap->rs485_tx_drain_interval = (bits * 1000 * 1000) / baud;

pl011_setup_status_masks(port, termios);

if (UART_ENABLE_MS(port, termios->c_cflag))
pl011_enable_ms(port);

if (port->rs485.flags & SER_RS485_ENABLED)
termios->c_cflag &= ~CRTSCTS;

/* first, disable everything */
old_cr = pl011_read(uap, REG_CR);
pl011_write(0, uap, REG_CR);
Expand Down Expand Up @@ -2124,6 +2226,41 @@ static int pl011_verify_port(struct uart_port *port, struct serial_struct *ser)
return ret;
}

static int pl011_rs485_config(struct uart_port *port,
struct serial_rs485 *rs485)
{
struct uart_amba_port *uap =
container_of(port, struct uart_amba_port, port);

/* pick sane settings if the user hasn't */
if (!(rs485->flags & SER_RS485_RTS_ON_SEND) ==
!(rs485->flags & SER_RS485_RTS_AFTER_SEND)) {
rs485->flags |= SER_RS485_RTS_ON_SEND;
rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
}
/* clamp the delays to [0, 100ms] */
rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
rs485->delay_rts_after_send = min(rs485->delay_rts_after_send, 100U);
memset(rs485->padding, 0, sizeof(rs485->padding));

if (port->rs485.flags & SER_RS485_ENABLED)
pl011_rs485_tx_stop(uap);

/* Set new configuration */
port->rs485 = *rs485;

/* Make sure auto RTS is disabled */
if (port->rs485.flags & SER_RS485_ENABLED) {
u32 cr = pl011_read(uap, REG_CR);

cr &= ~UART011_CR_RTSEN;
pl011_write(cr, uap, REG_CR);
port->status &= ~UPSTAT_AUTORTS;
}

return 0;
}

static const struct uart_ops amba_pl011_pops = {
.tx_empty = pl011_tx_empty,
.set_mctrl = pl011_set_mctrl,
Expand Down Expand Up @@ -2588,10 +2725,28 @@ static int pl011_find_free_port(void)
return -EBUSY;
}

static int pl011_get_rs485_mode(struct uart_amba_port *uap)
{
struct uart_port *port = &uap->port;
struct serial_rs485 *rs485 = &port->rs485;
int ret;

ret = uart_get_rs485_mode(port);
if (ret)
return ret;

/* clamp the delays to [0, 100ms] */
rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
rs485->delay_rts_after_send = min(rs485->delay_rts_after_send, 100U);

return 0;
}

static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
struct resource *mmiobase, int index)
{
void __iomem *base;
int ret;

base = devm_ioremap_resource(dev, mmiobase);
if (IS_ERR(base))
Expand All @@ -2608,6 +2763,10 @@ static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
uap->port.flags = UPF_BOOT_AUTOCONF;
uap->port.line = index;

ret = pl011_get_rs485_mode(uap);
if (ret)
return ret;

amba_ports[index] = uap;

return 0;
Expand Down Expand Up @@ -2665,7 +2824,7 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
uap->port.iotype = vendor->access_32b ? UPIO_MEM32 : UPIO_MEM;
uap->port.irq = dev->irq[0];
uap->port.ops = &amba_pl011_pops;

uap->port.rs485_config = pl011_rs485_config;
snprintf(uap->type, sizeof(uap->type), "PL011 rev%u", amba_rev(dev));

ret = pl011_setup_port(&dev->dev, uap, &dev->res, portnr);
Expand Down

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