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Commit 7cb92fd2 authored by Huang Shijie's avatar Huang Shijie Committed by Greg Kroah-Hartman
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serial: imx: optimization: remove the workqueues for DMA 



I worried that the delay of the sdma_run_channel0() maybe too long for
interrupt context, so I added the workqueues for RX/TX DMA.

But tested with bluetooth device, I find that the delay of sdma_run_channel0()
is about 8us (tested in imx6dl sabreauto board). I think the delay
is acceptable.

This patch removes the RX/TX workqueues for DMA, it makes the
code more clear.

Signed-off-by: default avatarHuang Shijie <b32955@freescale.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f0ef8834

drivers/tty/serial/imx.c

+10 −44
Original line number Diff line number Diff line
@@ -223,8 +223,7 @@ struct imx_port { 
	struct dma_chan		*dma_chan_rx, *dma_chan_tx;

	struct scatterlist	rx_sgl, tx_sgl[2];

	void			*rx_buf;

	unsigned int		rx_bytes, tx_bytes;

	struct work_struct	tsk_dma_rx, tsk_dma_tx;

	unsigned int		tx_bytes;

	unsigned int		dma_tx_nents;

	wait_queue_head_t	dma_wait;

};
@@ -505,32 +504,23 @@ static void dma_tx_callback(void *data) 
		dev_dbg(sport->port.dev, "exit in %s.\n", __func__);

		return;

	}



	schedule_work(&sport->tsk_dma_tx);

}



static void dma_tx_work(struct work_struct *w)

static void imx_dma_tx(struct imx_port *sport)

{

	struct imx_port *sport = container_of(w, struct imx_port, tsk_dma_tx);

	struct circ_buf *xmit = &sport->port.state->xmit;

	struct scatterlist *sgl = sport->tx_sgl;

	struct dma_async_tx_descriptor *desc;

	struct dma_chan	*chan = sport->dma_chan_tx;

	struct device *dev = sport->port.dev;

	enum dma_status status;

	unsigned long flags;

	int ret;



	status = dmaengine_tx_status(chan, (dma_cookie_t)0, NULL);

	if (DMA_IN_PROGRESS == status)

		return;



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

	sport->tx_bytes = uart_circ_chars_pending(xmit);

	if (sport->tx_bytes == 0) {

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

		return;

	}



	if (xmit->tail > xmit->head && xmit->head > 0) {

		sport->dma_tx_nents = 2;
@@ -542,7 +532,6 @@ static void dma_tx_work(struct work_struct *w) 
		sport->dma_tx_nents = 1;

		sg_init_one(sgl, xmit->buf + xmit->tail, sport->tx_bytes);

	}

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



	ret = dma_map_sg(dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);

	if (ret == 0) {
@@ -609,11 +598,7 @@ static void imx_start_tx(struct uart_port *port) 
	}



	if (sport->dma_is_enabled) {

		/*

		 * We may in the interrupt context, so arise a work_struct to

		 * do the real job.

		 */

		schedule_work(&sport->tsk_dma_tx);

		imx_dma_tx(sport);

		return;

	}
@@ -732,6 +717,7 @@ out: 
	return IRQ_HANDLED;

}



static int start_rx_dma(struct imx_port *sport);

/*

 * If the RXFIFO is filled with some data, and then we

 * arise a DMA operation to receive them.
@@ -750,7 +736,7 @@ static void imx_dma_rxint(struct imx_port *sport) 
		writel(temp, sport->port.membase + UCR1);



		/* tell the DMA to receive the data. */

		schedule_work(&sport->tsk_dma_rx);

		start_rx_dma(sport);

	}

}
@@ -872,22 +858,6 @@ static int imx_setup_ufcr(struct imx_port *sport, unsigned int mode) 
}



#define RX_BUF_SIZE	(PAGE_SIZE)

static int start_rx_dma(struct imx_port *sport);

static void dma_rx_work(struct work_struct *w)

{

	struct imx_port *sport = container_of(w, struct imx_port, tsk_dma_rx);

	struct tty_port *port = &sport->port.state->port;



	if (sport->rx_bytes) {

		tty_insert_flip_string(port, sport->rx_buf, sport->rx_bytes);

		tty_flip_buffer_push(port);

		sport->rx_bytes = 0;

	}



	if (sport->dma_is_rxing)

		start_rx_dma(sport);

}



static void imx_rx_dma_done(struct imx_port *sport)

{

	unsigned long temp;
@@ -919,6 +889,7 @@ static void dma_rx_callback(void *data) 
	struct imx_port *sport = data;

	struct dma_chan	*chan = sport->dma_chan_rx;

	struct scatterlist *sgl = &sport->rx_sgl;

	struct tty_port *port = &sport->port.state->port;

	struct dma_tx_state state;

	enum dma_status status;

	unsigned int count;
@@ -931,8 +902,10 @@ static void dma_rx_callback(void *data) 
	dev_dbg(sport->port.dev, "We get %d bytes.\n", count);



	if (count) {

		sport->rx_bytes = count;

		schedule_work(&sport->tsk_dma_rx);

		tty_insert_flip_string(port, sport->rx_buf, count);

		tty_flip_buffer_push(port);



		start_rx_dma(sport);

	} else

		imx_rx_dma_done(sport);

}
@@ -1014,7 +987,6 @@ static int imx_uart_dma_init(struct imx_port *sport) 
		ret = -ENOMEM;

		goto err;

	}

	sport->rx_bytes = 0;



	/* Prepare for TX : */

	sport->dma_chan_tx = dma_request_slave_channel(dev, "tx");
@@ -1045,11 +1017,7 @@ err: 
static void imx_enable_dma(struct imx_port *sport)

{

	unsigned long temp;

	struct tty_port *port = &sport->port.state->port;



	port->low_latency = 1;

	INIT_WORK(&sport->tsk_dma_tx, dma_tx_work);

	INIT_WORK(&sport->tsk_dma_rx, dma_rx_work);

	init_waitqueue_head(&sport->dma_wait);



	/* set UCR1 */
@@ -1070,7 +1038,6 @@ static void imx_enable_dma(struct imx_port *sport) 
static void imx_disable_dma(struct imx_port *sport)

{

	unsigned long temp;

	struct tty_port *port = &sport->port.state->port;



	/* clear UCR1 */

	temp = readl(sport->port.membase + UCR1);
@@ -1088,7 +1055,6 @@ static void imx_disable_dma(struct imx_port *sport) 
	writel(temp, sport->port.membase + UCR4);



	sport->dma_is_enabled = 0;

	port->low_latency = 0;

}



/* half the RX buffer size */