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spi: omap2_mcspi rxdma bugfix

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When data is read through DMA, the last element must be read separately
through the RX register.  It cannot be transferred by the DMA.  For
further details see e.g.  OMAP35x TRM (table 19-16).

Without the fix the driver causes extra clocks to be clocked to the bus
after DMA RX operations.  This can cause interesting behaviour with some
devices.

Signed-off-by: Juuso Oikarinen <[email protected]>
Signed-off-by: Eero Nurkkala <[email protected]>
[[email protected]: Simplified the patch while keeping the idea.]
Signed-off-by: Aaro Koskinen <[email protected]>
Signed-off-by: David Brownell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Eero Nurkkala 2009-07-29 15:02:12 -07:00 • committed by Linus Torvalds
commit 57c5c28dbc
1 changed files with 20 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

21
drivers/spi/omap2_mcspi.c
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@ -272,7 +272,7 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
if (rx != NULL) {
omap_set_dma_transfer_params(mcspi_dma->dma_rx_channel,
data_type, element_count, 1,
data_type, element_count - 1, 1,
OMAP_DMA_SYNC_ELEMENT,
mcspi_dma->dma_rx_sync_dev, 1);
@ -303,6 +303,25 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
if (rx != NULL) {
wait_for_completion(&mcspi_dma->dma_rx_completion);
dma_unmap_single(NULL, xfer->rx_dma, count, DMA_FROM_DEVICE);
omap2_mcspi_set_enable(spi, 0);
if (likely(mcspi_read_cs_reg(spi, OMAP2_MCSPI_CHSTAT0)
& OMAP2_MCSPI_CHSTAT_RXS)) {
u32 w;
w = mcspi_read_cs_reg(spi, OMAP2_MCSPI_RX0);
if (word_len <= 8)
((u8 *)xfer->rx_buf)[element_count - 1] = w;
else if (word_len <= 16)
((u16 *)xfer->rx_buf)[element_count - 1] = w;
else /* word_len <= 32 */
((u32 *)xfer->rx_buf)[element_count - 1] = w;
} else {
dev_err(&spi->dev, "DMA RX last word empty");
count -= (word_len <= 8) ? 1 :
(word_len <= 16) ? 2 :
/* word_len <= 32 */ 4;
}
omap2_mcspi_set_enable(spi, 1);
}
return count;
}