Skip to content

Commit

Permalink
atmel_spi: chain DMA transfers
Browse files Browse the repository at this point in the history 
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: Szilveszter Ordog <slipszi@gmail.com>
Acked-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  • Loading branch information
Silvester Erdeg authored and Linus Torvalds committed Feb 6, 2008
1 parent 1eed29d commit 154443c
Showing 1 changed file with 101 additions and 45 deletions.
146 changes: 101 additions & 45 deletions drivers/spi/atmel_spi.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -121,6 +123,48 @@ static void cs_deactivate(struct atmel_spi *as, struct spi_device *spi)
gpio_set_value(gpio, !active);
}

static inline int atmel_spi_xfer_is_last(struct spi_message *msg,
struct spi_transfer *xfer)
{
return msg->transfers.prev == &xfer->transfer_list;
}

static inline int atmel_spi_xfer_can_be_chained(struct spi_transfer *xfer)
{
return xfer->delay_usecs == 0 && !xfer->cs_change;
}

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 = 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 = xfer->tx_dma + xfer->len - len;
else {
*tx_dma = as->buffer_dma;
if (len > BUFFER_SIZE)
len = BUFFER_SIZE;
memset(as->buffer, 0, len);
dma_sync_single_for_device(&as->pdev->dev,
as->buffer_dma, len, DMA_TO_DEVICE);
}

*plen = len;
}

/*
* Submit next transfer for DMA.
* lock is held, spi irq is blocked
Expand All @@ -130,53 +174,68 @@ static void atmel_spi_next_xfer(struct spi_master *master,
{
struct atmel_spi *as = spi_master_get_devdata(master);
struct spi_transfer *xfer;
u32 len;
u32 len, remaining, total;
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;
}
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;

len = as->remaining_bytes;
if (xfer) {
len = xfer->len;
atmel_spi_next_xfer_data(master, xfer, &tx_dma, &rx_dma, &len);
remaining = xfer->len - len;

tx_dma = xfer->tx_dma + xfer->len - len;
rx_dma = xfer->rx_dma + xfer->len - len;
spi_writel(as, RPR, rx_dma);
spi_writel(as, TPR, tx_dma);

/* use scratch buffer only when rx or tx data is unspecified */
if (!xfer->rx_buf) {
rx_dma = as->buffer_dma;
if (len > BUFFER_SIZE)
len = BUFFER_SIZE;
}
if (!xfer->tx_buf) {
tx_dma = as->buffer_dma;
if (len > BUFFER_SIZE)
len = BUFFER_SIZE;
memset(as->buffer, 0, len);
dma_sync_single_for_device(&as->pdev->dev,
as->buffer_dma, len, DMA_TO_DEVICE);
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;
}

spi_writel(as, RPR, rx_dma);
spi_writel(as, TPR, tx_dma);
as->current_transfer = xfer;
as->current_remaining_bytes = remaining;

as->remaining_bytes -= len;
if (msg->spi->bits_per_word > 8)
len >>= 1;
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;

/* 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->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
Expand All @@ -186,17 +245,13 @@ 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,
" start xfer %p: len %u tx %p/%08x rx %p/%08x imr %03x\n",
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));
}

Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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)
Expand All @@ -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);
Expand Down

0 comments on commit 154443c

Please sign in to comment.