From: Eero Nurkkala <[email protected]> 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. OMAP3430 TRM.
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. Reported-by: Juuso Oikarinen <[email protected]> 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]> --- drivers/spi/omap2_mcspi.c | 21 ++++++++++++++++++++- 1 files changed, 20 insertions(+), 1 deletions(-) diff --git a/drivers/spi/omap2_mcspi.c b/drivers/spi/omap2_mcspi.c index d6d0c5d..0f640b0 100644 --- a/drivers/spi/omap2_mcspi.c +++ b/drivers/spi/omap2_mcspi.c @@ -269,7 +269,7 @@ 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); @@ -300,6 +300,25 @@ 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; } -- 1.5.4.3 ------------------------------------------------------------------------------ Crystal Reports - New Free Runtime and 30 Day Trial Check out the new simplified licensing option that enables unlimited royalty-free distribution of the report engine for externally facing server and web deployment. http://p.sf.net/sfu/businessobjects _______________________________________________ spi-devel-general mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/spi-devel-general
