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. 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]> --- drivers/spi/omap2_mcspi.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) --- a/drivers/spi/omap2_mcspi.c +++ b/drivers/spi/omap2_mcspi.c @@ -272,7 +272,7 @@ omap2_mcspi_txrx_dma(struct spi_device * 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 * 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; } ------------------------------------------------------------------------------ _______________________________________________ spi-devel-general mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/spi-devel-general
