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tty: serial: fsl_lpuart: Use scatter/gather DMA for Tx
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Drop PIO to DMA switching and use scatter/gather DMA for Tx path to improve
performance.

Some part of the code is borrowed from imx serial driver.

Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@bhuvanchandra @gregkh
bhuvanchandra authored and gregkh committed Aug 31, 2016
1 parent 5887ad4 commit 6250cc3
Showing 1 changed file with 113 additions and 144 deletions.
257 changes: 113 additions & 144 deletions drivers/tty/serial/fsl_lpuart.c
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Expand Up @@ -244,18 +244,18 @@ struct lpuart_port {
struct dma_chan *dma_rx_chan;
struct dma_async_tx_descriptor *dma_tx_desc;
struct dma_async_tx_descriptor *dma_rx_desc;
dma_addr_t dma_tx_buf_bus;
dma_cookie_t dma_tx_cookie;
dma_cookie_t dma_rx_cookie;
unsigned char *dma_tx_buf_virt;
unsigned int dma_tx_bytes;
unsigned int dma_rx_bytes;
int dma_tx_in_progress;
bool dma_tx_in_progress;
unsigned int dma_rx_timeout;
struct timer_list lpuart_timer;
struct scatterlist rx_sgl;
struct scatterlist rx_sgl, tx_sgl[2];
struct circ_buf rx_ring;
int rx_dma_rng_buf_len;
unsigned int dma_tx_nents;
wait_queue_head_t dma_wait;
};

static const struct of_device_id lpuart_dt_ids[] = {
Expand Down Expand Up @@ -316,103 +316,118 @@ static void lpuart32_stop_rx(struct uart_port *port)
lpuart32_write(temp & ~UARTCTRL_RE, port->membase + UARTCTRL);
}

static void lpuart_pio_tx(struct lpuart_port *sport)
static void lpuart_dma_tx(struct lpuart_port *sport)
{
struct circ_buf *xmit = &sport->port.state->xmit;
unsigned long flags;

spin_lock_irqsave(&sport->port.lock, flags);
struct scatterlist *sgl = sport->tx_sgl;
struct device *dev = sport->port.dev;
int ret;

while (!uart_circ_empty(xmit) &&
readb(sport->port.membase + UARTTCFIFO) < sport->txfifo_size) {
writeb(xmit->buf[xmit->tail], sport->port.membase + UARTDR);
xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
sport->port.icount.tx++;
}
if (sport->dma_tx_in_progress)
return;

if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
uart_write_wakeup(&sport->port);
sport->dma_tx_bytes = uart_circ_chars_pending(xmit);

if (uart_circ_empty(xmit))
writeb(readb(sport->port.membase + UARTCR5) | UARTCR5_TDMAS,
sport->port.membase + UARTCR5);
if (xmit->tail < xmit->head) {
sport->dma_tx_nents = 1;
sg_init_one(sgl, xmit->buf + xmit->tail, sport->dma_tx_bytes);
} else {
sport->dma_tx_nents = 2;
sg_init_table(sgl, 2);
sg_set_buf(sgl, xmit->buf + xmit->tail,
UART_XMIT_SIZE - xmit->tail);
sg_set_buf(sgl + 1, xmit->buf, xmit->head);
}

spin_unlock_irqrestore(&sport->port.lock, flags);
}
ret = dma_map_sg(dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
if (!ret) {
dev_err(dev, "DMA mapping error for TX.\n");
return;
}

static int lpuart_dma_tx(struct lpuart_port *sport, unsigned long count)
{
struct circ_buf *xmit = &sport->port.state->xmit;
dma_addr_t tx_bus_addr;

dma_sync_single_for_device(sport->port.dev, sport->dma_tx_buf_bus,
UART_XMIT_SIZE, DMA_TO_DEVICE);
sport->dma_tx_bytes = count & ~(sport->txfifo_size - 1);
tx_bus_addr = sport->dma_tx_buf_bus + xmit->tail;
sport->dma_tx_desc = dmaengine_prep_slave_single(sport->dma_tx_chan,
tx_bus_addr, sport->dma_tx_bytes,
sport->dma_tx_desc = dmaengine_prep_slave_sg(sport->dma_tx_chan, sgl,
sport->dma_tx_nents,
DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT);

if (!sport->dma_tx_desc) {
dev_err(sport->port.dev, "Not able to get desc for tx\n");
return -EIO;
dma_unmap_sg(dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
dev_err(dev, "Cannot prepare TX slave DMA!\n");
return;
}

sport->dma_tx_desc->callback = lpuart_dma_tx_complete;
sport->dma_tx_desc->callback_param = sport;
sport->dma_tx_in_progress = 1;
sport->dma_tx_in_progress = true;
sport->dma_tx_cookie = dmaengine_submit(sport->dma_tx_desc);
dma_async_issue_pending(sport->dma_tx_chan);

return 0;
}

static void lpuart_prepare_tx(struct lpuart_port *sport)
{
struct circ_buf *xmit = &sport->port.state->xmit;
unsigned long count = CIRC_CNT_TO_END(xmit->head,
xmit->tail, UART_XMIT_SIZE);

if (!count)
return;

if (count < sport->txfifo_size)
writeb(readb(sport->port.membase + UARTCR5) & ~UARTCR5_TDMAS,
sport->port.membase + UARTCR5);
else {
writeb(readb(sport->port.membase + UARTCR5) | UARTCR5_TDMAS,
sport->port.membase + UARTCR5);
lpuart_dma_tx(sport, count);
}
}

static void lpuart_dma_tx_complete(void *arg)
{
struct lpuart_port *sport = arg;
struct scatterlist *sgl = &sport->tx_sgl[0];
struct circ_buf *xmit = &sport->port.state->xmit;
unsigned long flags;

async_tx_ack(sport->dma_tx_desc);

spin_lock_irqsave(&sport->port.lock, flags);

dma_unmap_sg(sport->port.dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);

xmit->tail = (xmit->tail + sport->dma_tx_bytes) & (UART_XMIT_SIZE - 1);
sport->dma_tx_in_progress = 0;

sport->port.icount.tx += sport->dma_tx_bytes;
sport->dma_tx_in_progress = false;
spin_unlock_irqrestore(&sport->port.lock, flags);

if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
uart_write_wakeup(&sport->port);

lpuart_prepare_tx(sport);
if (waitqueue_active(&sport->dma_wait)) {
wake_up(&sport->dma_wait);
return;
}

spin_lock_irqsave(&sport->port.lock, flags);

if (!uart_circ_empty(xmit) && !uart_tx_stopped(&sport->port))
lpuart_dma_tx(sport);

spin_unlock_irqrestore(&sport->port.lock, flags);
}

static int lpuart_dma_tx_request(struct uart_port *port)
{
struct lpuart_port *sport = container_of(port,
struct lpuart_port, port);
struct dma_slave_config dma_tx_sconfig = {};
int ret;

dma_tx_sconfig.dst_addr = sport->port.mapbase + UARTDR;
dma_tx_sconfig.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
dma_tx_sconfig.dst_maxburst = 1;
dma_tx_sconfig.direction = DMA_MEM_TO_DEV;
ret = dmaengine_slave_config(sport->dma_tx_chan, &dma_tx_sconfig);

if (ret) {
dev_err(sport->port.dev,
"DMA slave config failed, err = %d\n", ret);
return ret;
}

return 0;
}

static void lpuart_flush_buffer(struct uart_port *port)
{
struct lpuart_port *sport = container_of(port, struct lpuart_port, port);

if (sport->lpuart_dma_tx_use) {
if (sport->dma_tx_in_progress) {
dma_unmap_sg(sport->port.dev, &sport->tx_sgl[0],
sport->dma_tx_nents, DMA_TO_DEVICE);
sport->dma_tx_in_progress = false;
}
dmaengine_terminate_all(sport->dma_tx_chan);
sport->dma_tx_in_progress = 0;
}
}

Expand Down Expand Up @@ -469,8 +484,8 @@ static void lpuart_start_tx(struct uart_port *port)
writeb(temp | UARTCR2_TIE, port->membase + UARTCR2);

if (sport->lpuart_dma_tx_use) {
if (!uart_circ_empty(xmit) && !sport->dma_tx_in_progress)
lpuart_prepare_tx(sport);
if (!uart_circ_empty(xmit) && !uart_tx_stopped(port))
lpuart_dma_tx(sport);
} else {
if (readb(port->membase + UARTSR1) & UARTSR1_TDRE)
lpuart_transmit_buffer(sport);
Expand All @@ -489,6 +504,29 @@ static void lpuart32_start_tx(struct uart_port *port)
lpuart32_transmit_buffer(sport);
}

/* return TIOCSER_TEMT when transmitter is not busy */
static unsigned int lpuart_tx_empty(struct uart_port *port)
{
struct lpuart_port *sport = container_of(port,
struct lpuart_port, port);
unsigned char sr1 = readb(port->membase + UARTSR1);
unsigned char sfifo = readb(port->membase + UARTSFIFO);

if (sport->dma_tx_in_progress)
return 0;

if (sr1 & UARTSR1_TC && sfifo & UARTSFIFO_TXEMPT)
return TIOCSER_TEMT;

return 0;
}

static unsigned int lpuart32_tx_empty(struct uart_port *port)
{
return (lpuart32_read(port->membase + UARTSTAT) & UARTSTAT_TC) ?
TIOCSER_TEMT : 0;
}

static irqreturn_t lpuart_txint(int irq, void *dev_id)
{
struct lpuart_port *sport = dev_id;
Expand Down Expand Up @@ -662,12 +700,8 @@ static irqreturn_t lpuart_int(int irq, void *dev_id)
if (sts & UARTSR1_RDRF)
lpuart_rxint(irq, dev_id);

if (sts & UARTSR1_TDRE) {
if (sport->lpuart_dma_tx_use)
lpuart_pio_tx(sport);
else
lpuart_txint(irq, dev_id);
}
if (sts & UARTSR1_TDRE)
lpuart_txint(irq, dev_id);

return IRQ_HANDLED;
}
Expand All @@ -692,29 +726,6 @@ static irqreturn_t lpuart32_int(int irq, void *dev_id)
return IRQ_HANDLED;
}

/* return TIOCSER_TEMT when transmitter is not busy */
static unsigned int lpuart_tx_empty(struct uart_port *port)
{
struct lpuart_port *sport = container_of(port,
struct lpuart_port, port);
unsigned char sr1 = readb(port->membase + UARTSR1);
unsigned char sfifo = readb(port->membase + UARTSFIFO);

if (sport->dma_tx_in_progress)
return 0;

if (sr1 & UARTSR1_TC && sfifo & UARTSFIFO_TXEMPT)
return TIOCSER_TEMT;

return 0;
}

static unsigned int lpuart32_tx_empty(struct uart_port *port)
{
return (lpuart32_read(port->membase + UARTSTAT) & UARTSTAT_TC) ?
TIOCSER_TEMT : 0;
}

static void lpuart_copy_rx_to_tty(struct lpuart_port *sport)
{
struct tty_port *port = &sport->port.state->port;
Expand Down Expand Up @@ -890,18 +901,6 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
return 0;
}

static void lpuart_dma_tx_free(struct uart_port *port)
{
struct lpuart_port *sport = container_of(port,
struct lpuart_port, port);

dma_unmap_single(sport->port.dev, sport->dma_tx_buf_bus,
UART_XMIT_SIZE, DMA_TO_DEVICE);

sport->dma_tx_buf_bus = 0;
sport->dma_tx_buf_virt = NULL;
}

static void lpuart_dma_rx_free(struct uart_port *port)
{
struct lpuart_port *sport = container_of(port,
Expand Down Expand Up @@ -1061,44 +1060,6 @@ static void lpuart32_setup_watermark(struct lpuart_port *sport)
lpuart32_write(ctrl_saved, sport->port.membase + UARTCTRL);
}

static int lpuart_dma_tx_request(struct uart_port *port)
{
struct lpuart_port *sport = container_of(port,
struct lpuart_port, port);
struct dma_slave_config dma_tx_sconfig;
dma_addr_t dma_bus;
unsigned char *dma_buf;
int ret;

dma_bus = dma_map_single(sport->dma_tx_chan->device->dev,
sport->port.state->xmit.buf,
UART_XMIT_SIZE, DMA_TO_DEVICE);

if (dma_mapping_error(sport->dma_tx_chan->device->dev, dma_bus)) {
dev_err(sport->port.dev, "dma_map_single tx failed\n");
return -ENOMEM;
}

dma_buf = sport->port.state->xmit.buf;
dma_tx_sconfig.dst_addr = sport->port.mapbase + UARTDR;
dma_tx_sconfig.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
dma_tx_sconfig.dst_maxburst = sport->txfifo_size;
dma_tx_sconfig.direction = DMA_MEM_TO_DEV;
ret = dmaengine_slave_config(sport->dma_tx_chan, &dma_tx_sconfig);

if (ret < 0) {
dev_err(sport->port.dev,
"Dma slave config failed, err = %d\n", ret);
return ret;
}

sport->dma_tx_buf_virt = dma_buf;
sport->dma_tx_buf_bus = dma_bus;
sport->dma_tx_in_progress = 0;

return 0;
}

static void rx_dma_timer_init(struct lpuart_port *sport)
{
setup_timer(&sport->lpuart_timer, lpuart_timer_func,
Expand Down Expand Up @@ -1151,6 +1112,7 @@ static int lpuart_startup(struct uart_port *port)
}

if (sport->dma_tx_chan && !lpuart_dma_tx_request(port)) {
init_waitqueue_head(&sport->dma_wait);
sport->lpuart_dma_tx_use = true;
temp = readb(port->membase + UARTCR5);
writeb(temp | UARTCR5_TDMAS, port->membase + UARTCR5);
Expand Down Expand Up @@ -1220,8 +1182,15 @@ static void lpuart_shutdown(struct uart_port *port)
lpuart_dma_rx_free(&sport->port);
}

if (sport->lpuart_dma_tx_use)
lpuart_dma_tx_free(&sport->port);
if (sport->lpuart_dma_tx_use) {
if (wait_event_interruptible(sport->dma_wait,
!sport->dma_tx_in_progress) != false) {
sport->dma_tx_in_progress = false;
dmaengine_terminate_all(sport->dma_tx_chan);
}

lpuart_stop_tx(port);
}
}

static void lpuart32_shutdown(struct uart_port *port)
Expand Down

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