OpenE2K
/
linux
6
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

spi: davinci: use rx buffer as dummy tx buffer 

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>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Frode Isaksen 2017-02-23 19:01:58 +01:00 committed by Mark Brown
parent 3e2e125844
commit 6b3a631e7f
1 changed files with 7 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/spi/spi-davinci.c
View File

@ -655,6 +655,12 @@ 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);
@ -957,7 +963,7 @@ 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;