spi: davinci: do not use temporary buffer if no transmit data provided
Remove usage of temporary buffer when no transmit data is provided.
Instead, use the transmit register itself as the source of data.
By choosing the transmit register itself as the source of data, this
patch helps remove unnecessary accesses to memory when no real data
is being transmitted.
Signed-off-by: Brian Niebuhr <bniebuhr@efjohnson.com>
Tested-By: Michael Williamson <michael.williamson@criticallink.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
diff --git a/drivers/spi/davinci_spi.c b/drivers/spi/davinci_spi.c
index a5f03dd..f512939 100644
--- a/drivers/spi/davinci_spi.c
+++ b/drivers/spi/davinci_spi.c
@@ -38,8 +38,6 @@
#define CS_DEFAULT 0xFF
-#define SPI_BUFSIZ (SMP_CACHE_BYTES + 1)
-
#define SPIFMT_PHASE_MASK BIT(16)
#define SPIFMT_POLARITY_MASK BIT(17)
#define SPIFMT_DISTIMER_MASK BIT(18)
@@ -140,7 +138,6 @@
const void *tx;
void *rx;
- u8 *tmp_buf;
int rcount;
int wcount;
struct davinci_spi_dma dma_channels;
@@ -718,7 +715,7 @@
{
struct davinci_spi *davinci_spi;
int int_status = 0;
- int count, temp_count;
+ int count;
struct davinci_spi_dma *davinci_spi_dma;
int data_type, ret;
unsigned long tx_reg, rx_reg;
@@ -750,6 +747,18 @@
/* Enable SPI */
set_io_bits(davinci_spi->base + SPIGCR1, SPIGCR1_SPIENA_MASK);
+ /*
+ * Transmit DMA setup
+ *
+ * If there is transmit data, map the transmit buffer, set it as the
+ * source of data and set the source B index to data size.
+ * If there is no transmit data, set the transmit register as the
+ * source of data, and set the source B index to zero.
+ *
+ * The destination is always the transmit register itself. And the
+ * destination never increments.
+ */
+
if (t->tx_buf) {
t->tx_dma = dma_map_single(&spi->dev, (void *)t->tx_buf, count,
DMA_TO_DEVICE);
@@ -758,25 +767,15 @@
" TX buffer\n", count);
return -ENOMEM;
}
- temp_count = count;
- } else {
- /* We need TX clocking for RX transaction */
- t->tx_dma = dma_map_single(&spi->dev,
- (void *)davinci_spi->tmp_buf, count + 1,
- DMA_TO_DEVICE);
- if (dma_mapping_error(&spi->dev, t->tx_dma)) {
- dev_dbg(sdev, "Unable to DMA map a %d bytes"
- " TX tmp buffer\n", count);
- return -ENOMEM;
- }
- temp_count = count + 1;
}
edma_set_transfer_params(davinci_spi_dma->dma_tx_channel,
- data_type, temp_count, 1, 0, ASYNC);
+ data_type, count, 1, 0, ASYNC);
edma_set_dest(davinci_spi_dma->dma_tx_channel, tx_reg, INCR, W8BIT);
- edma_set_src(davinci_spi_dma->dma_tx_channel, t->tx_dma, INCR, W8BIT);
- edma_set_src_index(davinci_spi_dma->dma_tx_channel, data_type, 0);
+ edma_set_src(davinci_spi_dma->dma_tx_channel,
+ t->tx_buf ? t->tx_dma : tx_reg, INCR, W8BIT);
+ edma_set_src_index(davinci_spi_dma->dma_tx_channel,
+ t->tx_buf ? data_type : 0, 0);
edma_set_dest_index(davinci_spi_dma->dma_tx_channel, 0, 0);
if (t->rx_buf) {
@@ -818,7 +817,8 @@
wait_for_completion_interruptible(
&davinci_spi_dma->dma_rx_completion);
- dma_unmap_single(NULL, t->tx_dma, temp_count, DMA_TO_DEVICE);
+ if (t->tx_buf)
+ dma_unmap_single(NULL, t->tx_dma, count, DMA_TO_DEVICE);
if (t->rx_buf)
dma_unmap_single(NULL, t->rx_dma, count, DMA_FROM_DEVICE);
@@ -906,17 +906,10 @@
if (ret)
goto unmap_io;
- /* Allocate tmp_buf for tx_buf */
- davinci_spi->tmp_buf = kzalloc(SPI_BUFSIZ, GFP_KERNEL);
- if (davinci_spi->tmp_buf == NULL) {
- ret = -ENOMEM;
- goto irq_free;
- }
-
davinci_spi->bitbang.master = spi_master_get(master);
if (davinci_spi->bitbang.master == NULL) {
ret = -ENODEV;
- goto free_tmp_buf;
+ goto irq_free;
}
davinci_spi->clk = clk_get(&pdev->dev, NULL);
@@ -1027,8 +1020,6 @@
clk_put(davinci_spi->clk);
put_master:
spi_master_put(master);
-free_tmp_buf:
- kfree(davinci_spi->tmp_buf);
irq_free:
free_irq(davinci_spi->irq, davinci_spi);
unmap_io:
@@ -1063,7 +1054,6 @@
clk_disable(davinci_spi->clk);
clk_put(davinci_spi->clk);
spi_master_put(master);
- kfree(davinci_spi->tmp_buf);
free_irq(davinci_spi->irq, davinci_spi);
iounmap(davinci_spi->base);
release_mem_region(davinci_spi->pbase, davinci_spi->region_size);