Commit 154443c7 authored by Silvester Erdeg's avatar Silvester Erdeg Committed by Linus Torvalds
Browse files

atmel_spi: chain DMA transfers 



Add support for chained transfers in the atmel_spi driver, letting the DMA
controller switch to the next buffer pair without CPU intervention.  This
reduced I/O latencies by about 2% in one bulk I/O test.  It should also help
work around several interrelated errata affecting chipselect 0 on at91rm9200
chips.

Almost all of the changes are in the reworked atmel_spi_next_xfer() function.
That's now called with the driver in one of three states:

 1. It isn't transferring anything (in which case the first transfer
    of the current message is going to be sent)
 2. It has finished transfering a non-chainable transfer (in which
    case it will go to the next transfer in the message)
 3. It has finished transfering a chained transfer (in which case the
    next transfer is already queued)

After that it will queue the next transfer if it can be chained.

Signed-off-by: default avatarSzilveszter Ordog <slipszi@gmail.com>
Acked-by: default avatarHaavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1eed29df

drivers/spi/atmel_spi.c

+101 −45
Original line number Diff line number Diff line
@@ -51,7 +51,9 @@ struct atmel_spi { 
	u8			stopping;

	struct list_head	queue;

	struct spi_transfer	*current_transfer;

	unsigned long		remaining_bytes;

	unsigned long		current_remaining_bytes;

	struct spi_transfer	*next_transfer;

	unsigned long		next_remaining_bytes;



	void			*buffer;

	dma_addr_t		buffer_dma;
@@ -121,43 +123,38 @@ static void cs_deactivate(struct atmel_spi *as, struct spi_device *spi) 
		gpio_set_value(gpio, !active);

}



/*

 * Submit next transfer for DMA.

 * lock is held, spi irq is blocked

 */

static void atmel_spi_next_xfer(struct spi_master *master,

				struct spi_message *msg)

static inline int atmel_spi_xfer_is_last(struct spi_message *msg,

					struct spi_transfer *xfer)

{

	struct atmel_spi	*as = spi_master_get_devdata(master);

	struct spi_transfer	*xfer;

	u32			len;

	dma_addr_t		tx_dma, rx_dma;



	xfer = as->current_transfer;

	if (!xfer || as->remaining_bytes == 0) {

		if (xfer)

			xfer = list_entry(xfer->transfer_list.next,

					struct spi_transfer, transfer_list);

		else

			xfer = list_entry(msg->transfers.next,

					struct spi_transfer, transfer_list);

		as->remaining_bytes = xfer->len;

		as->current_transfer = xfer;

	return msg->transfers.prev == &xfer->transfer_list;

}



	len = as->remaining_bytes;

static inline int atmel_spi_xfer_can_be_chained(struct spi_transfer *xfer)

{

	return xfer->delay_usecs == 0 && !xfer->cs_change;

}



	tx_dma = xfer->tx_dma + xfer->len - len;

	rx_dma = xfer->rx_dma + xfer->len - len;

static void atmel_spi_next_xfer_data(struct spi_master *master,

				struct spi_transfer *xfer,

				dma_addr_t *tx_dma,

				dma_addr_t *rx_dma,

				u32 *plen)

{

	struct atmel_spi	*as = spi_master_get_devdata(master);

	u32			len = *plen;



	/* use scratch buffer only when rx or tx data is unspecified */

	if (!xfer->rx_buf) {

		rx_dma = as->buffer_dma;

	if (xfer->rx_buf)

		*rx_dma = xfer->rx_dma + xfer->len - len;

	else {

		*rx_dma = as->buffer_dma;

		if (len > BUFFER_SIZE)

			len = BUFFER_SIZE;

	}

	if (!xfer->tx_buf) {

		tx_dma = as->buffer_dma;

	if (xfer->tx_buf)

		*tx_dma = xfer->tx_dma + xfer->len - len;

	else {

		*tx_dma = as->buffer_dma;

		if (len > BUFFER_SIZE)

			len = BUFFER_SIZE;

		memset(as->buffer, 0, len);
@@ -165,18 +162,80 @@ static void atmel_spi_next_xfer(struct spi_master *master, 
				as->buffer_dma, len, DMA_TO_DEVICE);

	}



	*plen = len;

}



/*

 * Submit next transfer for DMA.

 * lock is held, spi irq is blocked

 */

static void atmel_spi_next_xfer(struct spi_master *master,

				struct spi_message *msg)

{

	struct atmel_spi	*as = spi_master_get_devdata(master);

	struct spi_transfer	*xfer;

	u32			len, remaining, total;

	dma_addr_t		tx_dma, rx_dma;



	if (!as->current_transfer)

		xfer = list_entry(msg->transfers.next,

				struct spi_transfer, transfer_list);

	else if (!as->next_transfer)

		xfer = list_entry(as->current_transfer->transfer_list.next,

				struct spi_transfer, transfer_list);

	else

		xfer = NULL;



	if (xfer) {

		len = xfer->len;

		atmel_spi_next_xfer_data(master, xfer, &tx_dma, &rx_dma, &len);

		remaining = xfer->len - len;



		spi_writel(as, RPR, rx_dma);

		spi_writel(as, TPR, tx_dma);



	as->remaining_bytes -= len;

		if (msg->spi->bits_per_word > 8)

			len >>= 1;

		spi_writel(as, RCR, len);

		spi_writel(as, TCR, len);

	} else {

		xfer = as->next_transfer;

		remaining = as->next_remaining_bytes;

	}



	/* REVISIT: when xfer->delay_usecs == 0, the PDC "next transfer"

	 * mechanism might help avoid the IRQ latency between transfers

	 * (and improve the nCS0 errata handling on at91rm9200 chips)

	 *

	 * We're also waiting for ENDRX before we start the next

	as->current_transfer = xfer;

	as->current_remaining_bytes = remaining;



	if (remaining > 0)

		len = remaining;

	else if (!atmel_spi_xfer_is_last(msg, xfer) &&

		atmel_spi_xfer_can_be_chained(xfer)) {

		xfer = list_entry(xfer->transfer_list.next,

				struct spi_transfer, transfer_list);

		len = xfer->len;

	} else

		xfer = NULL;



	as->next_transfer = xfer;



	if (xfer) {

		total = len;

		atmel_spi_next_xfer_data(master, xfer, &tx_dma, &rx_dma, &len);

		as->next_remaining_bytes = total - len;



		spi_writel(as, RNPR, rx_dma);

		spi_writel(as, TNPR, tx_dma);



		if (msg->spi->bits_per_word > 8)

			len >>= 1;

		spi_writel(as, RNCR, len);

		spi_writel(as, TNCR, len);

	} else {

		spi_writel(as, RNCR, 0);

		spi_writel(as, TNCR, 0);

	}



	/* REVISIT: We're waiting for ENDRX before we start the next

	 * transfer because we need to handle some difficult timing

	 * issues otherwise. If we wait for ENDTX in one transfer and

	 * then starts waiting for ENDRX in the next, it's difficult
@@ -186,8 +245,6 @@ static void atmel_spi_next_xfer(struct spi_master *master, 
	 *

	 * It should be doable, though. Just not now...

	 */

	spi_writel(as, TNCR, 0);

	spi_writel(as, RNCR, 0);

	spi_writel(as, IER, SPI_BIT(ENDRX) | SPI_BIT(OVRES));



	dev_dbg(&msg->spi->dev,
@@ -195,8 +252,6 @@ static void atmel_spi_next_xfer(struct spi_master *master, 
		xfer, xfer->len, xfer->tx_buf, xfer->tx_dma,

		xfer->rx_buf, xfer->rx_dma, spi_readl(as, IMR));



	spi_writel(as, RCR, len);

	spi_writel(as, TCR, len);

	spi_writel(as, PTCR, SPI_BIT(TXTEN) | SPI_BIT(RXTEN));

}
@@ -294,6 +349,7 @@ atmel_spi_msg_done(struct spi_master *master, struct atmel_spi *as, 
	spin_lock(&as->lock);



	as->current_transfer = NULL;

	as->next_transfer = NULL;



	/* continue if needed */

	if (list_empty(&as->queue) || as->stopping)
@@ -377,7 +433,7 @@ atmel_spi_interrupt(int irq, void *dev_id) 


		spi_writel(as, IDR, pending);



		if (as->remaining_bytes == 0) {

		if (as->current_remaining_bytes == 0) {

			msg->actual_length += xfer->len;



			if (!msg->is_dma_mapped)
@@ -387,7 +443,7 @@ atmel_spi_interrupt(int irq, void *dev_id) 
			if (xfer->delay_usecs)

				udelay(xfer->delay_usecs);



			if (msg->transfers.prev == &xfer->transfer_list) {

			if (atmel_spi_xfer_is_last(msg, xfer)) {

				/* report completed message */

				atmel_spi_msg_done(master, as, msg, 0,

						xfer->cs_change);

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