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[v2,3/6] spi: davinci: use rx buffer as dummy tx buffer

Message ID 1487327904-28311-4-git-send-email-fisaksen@baylibre.com (mailing list archive)
State Accepted
Commit 6b3a631e7f8eca75a987ed760898d28fb3628143
Headers show

Commit Message

Frode Isaksen Feb. 17, 2017, 10:38 a.m. UTC 
When doing rx-only transfer, the transfer will fail
if the number of SG entries exceeds 20.
This happens because the eDMA DMA engine is limited
to 20 SG entries in one transaction, and when the
DMA transcation is resumed (which takes > 150us),
rx errors occurs because the slave is still transmitting.
Fix this by using the rx buffer as the dummy tx buffer,
so that resuming the rx transcation happens at the same
time as resuming the tx transcation.

Signed-off-by: Frode Isaksen <fisaksen@baylibre.com>
---
 drivers/spi/spi-davinci.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
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Patch

diff --git a/drivers/spi/spi-davinci.c b/drivers/spi/spi-davinci.c
index 9823908..2632ae0 100644
--- a/drivers/spi/spi-davinci.c
+++ b/drivers/spi/spi-davinci.c
@@ -656,6 +656,12 @@  static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t)
 		if (!rxdesc)
 			goto err_desc;
 
+		if (!t->tx_buf) {
+			/* use rx buffer as dummy tx buffer */
+			t->tx_sg.sgl = t->rx_sg.sgl;
+			t->tx_sg.nents = t->rx_sg.nents;
+		}
+
 		txdesc = dmaengine_prep_slave_sg(dspi->dma_tx,
 				t->tx_sg.sgl, t->tx_sg.nents, DMA_MEM_TO_DEV,
 				DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
@@ -958,7 +964,7 @@  static int davinci_spi_probe(struct platform_device *pdev)
 	master->bus_num = pdev->id;
 	master->num_chipselect = pdata->num_chipselect;
 	master->bits_per_word_mask = SPI_BPW_RANGE_MASK(2, 16);
-	master->flags = (SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX);
+	master->flags = SPI_MASTER_MUST_RX;
 	master->setup = davinci_spi_setup;
 	master->cleanup = davinci_spi_cleanup;
 	master->can_dma = davinci_spi_can_dma;