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serial: imx: implement rts delaying for rs485
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This adds support for delays between assertion of RTS (which is supposed
to enable the rs485 transmitter) and sending as well as between the last
send char and deassertionof RTS.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20200714093012.21621-2-uwe@kleine-koenig.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@gregkh
Uwe Kleine-König authored and gregkh committed Jul 21, 2020
1 parent 23a98b6 commit cb1a609
Showing 1 changed file with 121 additions and 36 deletions.
157 changes: 121 additions & 36 deletions drivers/tty/serial/imx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,13 @@ struct imx_uart_data {
enum imx_uart_type devtype;
};

enum imx_tx_state {
OFF,
WAIT_AFTER_RTS,
SEND,
WAIT_AFTER_SEND,
};

struct imx_port {
struct uart_port port;
struct timer_list timer;
Expand Down Expand Up @@ -224,6 +231,11 @@ struct imx_port {
unsigned int dma_tx_nents;
unsigned int saved_reg[10];
bool context_saved;

enum imx_tx_state tx_state;
unsigned long tx_state_next_change;
struct timer_list trigger_start_tx;
struct timer_list trigger_stop_tx;
};

struct imx_port_ucrs {
Expand Down Expand Up @@ -427,7 +439,10 @@ static void imx_uart_start_rx(struct uart_port *port)
static void imx_uart_stop_tx(struct uart_port *port)
{
struct imx_port *sport = (struct imx_port *)port;
u32 ucr1;
u32 ucr1, ucr4, usr2;

if (sport->tx_state == OFF)
return;

/*
* We are maybe in the SMP context, so if the DMA TX thread is running
Expand All @@ -439,21 +454,46 @@ static void imx_uart_stop_tx(struct uart_port *port)
ucr1 = imx_uart_readl(sport, UCR1);
imx_uart_writel(sport, ucr1 & ~UCR1_TRDYEN, UCR1);

/* in rs485 mode disable transmitter if shifter is empty */
if (port->rs485.flags & SER_RS485_ENABLED &&
imx_uart_readl(sport, USR2) & USR2_TXDC) {
u32 ucr2 = imx_uart_readl(sport, UCR2), ucr4;
if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
imx_uart_rts_active(sport, &ucr2);
else
imx_uart_rts_inactive(sport, &ucr2);
imx_uart_writel(sport, ucr2, UCR2);
usr2 = imx_uart_readl(sport, USR2);
if (!(usr2 & USR2_TXDC)) {
/* The shifter is still busy, so retry once TC triggers */
return;
}

imx_uart_start_rx(port);
ucr4 = imx_uart_readl(sport, UCR4);
ucr4 &= ~UCR4_TCEN;
imx_uart_writel(sport, ucr4, UCR4);

ucr4 = imx_uart_readl(sport, UCR4);
ucr4 &= ~UCR4_TCEN;
imx_uart_writel(sport, ucr4, UCR4);
/* in rs485 mode disable transmitter */
if (port->rs485.flags & SER_RS485_ENABLED) {
if (sport->tx_state == SEND) {
sport->tx_state = WAIT_AFTER_SEND;
sport->tx_state_next_change =
jiffies + DIV_ROUND_UP(port->rs485.delay_rts_after_send * HZ, 1000);
}

if (sport->tx_state == WAIT_AFTER_RTS ||
(sport->tx_state == WAIT_AFTER_SEND &&
time_after_eq(jiffies, sport->tx_state_next_change))) {
u32 ucr2;

del_timer(&sport->trigger_start_tx);

ucr2 = imx_uart_readl(sport, UCR2);
if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
imx_uart_rts_active(sport, &ucr2);
else
imx_uart_rts_inactive(sport, &ucr2);
imx_uart_writel(sport, ucr2, UCR2);

imx_uart_start_rx(port);

sport->tx_state = OFF;
} else if (sport->tx_state == WAIT_AFTER_SEND) {
mod_timer(&sport->trigger_stop_tx, sport->tx_state_next_change);
}
} else {
sport->tx_state = OFF;
}
}

Expand Down Expand Up @@ -651,28 +691,53 @@ static void imx_uart_start_tx(struct uart_port *port)
if (!sport->port.x_char && uart_circ_empty(&port->state->xmit))
return;

/*
* We cannot simply do nothing here if sport->tx_state == SEND already
* because UCR1_TXMPTYEN might already have been cleared in
* imx_uart_stop_tx(), but tx_state is still SEND.
*/

if (port->rs485.flags & SER_RS485_ENABLED) {
u32 ucr2;
if (sport->tx_state == OFF) {
u32 ucr2 = imx_uart_readl(sport, UCR2);
if (port->rs485.flags & SER_RS485_RTS_ON_SEND)
imx_uart_rts_active(sport, &ucr2);
else
imx_uart_rts_inactive(sport, &ucr2);
imx_uart_writel(sport, ucr2, UCR2);

ucr2 = imx_uart_readl(sport, UCR2);
if (port->rs485.flags & SER_RS485_RTS_ON_SEND)
imx_uart_rts_active(sport, &ucr2);
else
imx_uart_rts_inactive(sport, &ucr2);
imx_uart_writel(sport, ucr2, UCR2);
if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
imx_uart_stop_rx(port);

if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
imx_uart_stop_rx(port);
sport->tx_state = WAIT_AFTER_RTS;
sport->tx_state_next_change =
jiffies + DIV_ROUND_UP(port->rs485.delay_rts_before_send * HZ, 1000);
}

/*
* Enable transmitter and shifter empty irq only if DMA is off.
* In the DMA case this is done in the tx-callback.
*/
if (!sport->dma_is_enabled) {
u32 ucr4 = imx_uart_readl(sport, UCR4);
ucr4 |= UCR4_TCEN;
imx_uart_writel(sport, ucr4, UCR4);
if (sport->tx_state == WAIT_AFTER_SEND ||
(sport->tx_state == WAIT_AFTER_RTS &&
time_after_eq(jiffies, sport->tx_state_next_change))) {

del_timer(&sport->trigger_stop_tx);
/*
* Enable transmitter and shifter empty irq only if DMA
* is off. In the DMA case this is done in the
* tx-callback.
*/
if (!sport->dma_is_enabled) {
u32 ucr4 = imx_uart_readl(sport, UCR4);
ucr4 |= UCR4_TCEN;
imx_uart_writel(sport, ucr4, UCR4);
}

sport->tx_state = SEND;

} else if (sport->tx_state == WAIT_AFTER_RTS) {
mod_timer(&sport->trigger_start_tx, sport->tx_state_next_change);
return;
}
} else {
sport->tx_state = SEND;
}

if (!sport->dma_is_enabled) {
Expand Down Expand Up @@ -1630,7 +1695,6 @@ imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,

if (termios->c_cflag & CRTSCTS)
ucr2 &= ~UCR2_IRTS;

if (termios->c_cflag & CSTOPB)
ucr2 |= UCR2_STPB;
if (termios->c_cflag & PARENB) {
Expand Down Expand Up @@ -1857,10 +1921,6 @@ static int imx_uart_rs485_config(struct uart_port *port,
struct imx_port *sport = (struct imx_port *)port;
u32 ucr2;

/* unimplemented */
rs485conf->delay_rts_before_send = 0;
rs485conf->delay_rts_after_send = 0;

/* RTS is required to control the transmitter */
if (!sport->have_rtscts && !sport->have_rtsgpio)
rs485conf->flags &= ~SER_RS485_ENABLED;
Expand Down Expand Up @@ -2223,6 +2283,28 @@ static void imx_uart_probe_pdata(struct imx_port *sport,
sport->have_rtscts = 1;
}

static void imx_trigger_start_tx(struct timer_list *t)
{
struct imx_port *sport = from_timer(sport, t, trigger_start_tx);
unsigned long flags;

spin_lock_irqsave(&sport->port.lock, flags);
if (sport->tx_state == WAIT_AFTER_RTS)
imx_uart_start_tx(&sport->port);
spin_unlock_irqrestore(&sport->port.lock, flags);
}

static void imx_trigger_stop_tx(struct timer_list *t)
{
struct imx_port *sport = from_timer(sport, t, trigger_stop_tx);
unsigned long flags;

spin_lock_irqsave(&sport->port.lock, flags);
if (sport->tx_state == WAIT_AFTER_SEND)
imx_uart_stop_tx(&sport->port);
spin_unlock_irqrestore(&sport->port.lock, flags);
}

static int imx_uart_probe(struct platform_device *pdev)
{