In the TX_ONLY transfer, the SPI controller also receives data simultaneously and saves them in the rx register. After the TX_ONLY transfer, the rx register will hold the random data received during the last tx transaction.
If the direct following transfer is RX_ONLY, this random data has the possibility to affect this transfer like this: When the SPI controller is changed from TX_ONLY to RX_ONLY, the random data makes the rx register full immediately and triggers a dummy write automatically(in SPI RX_ONLY transfers, we need a dummy write to trigger the first transaction). So the first data received in the RX_ONLY transfer will be that random data instead of something meaningful. We can avoid this by inserting a Disable/Re-enable toggle of the channel after the TX_ONLY transfer, since it purges the rx register. Signed-off-by: Jason Wang <[email protected]> Tested-by: Grazvydas Ignotas <[email protected]> Acked-by: Tony Lindgren <[email protected]> --- Hi Grant, The touchpanel driver can't work correctly on the omap3evm platform, This is due to a omap2_mcspi driver issue, now fix it. drivers/spi/omap2_mcspi.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) diff --git a/drivers/spi/omap2_mcspi.c b/drivers/spi/omap2_mcspi.c index b3a94ca..43fab41 100644 --- a/drivers/spi/omap2_mcspi.c +++ b/drivers/spi/omap2_mcspi.c @@ -644,6 +644,12 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer) } else if (mcspi_wait_for_reg_bit(chstat_reg, OMAP2_MCSPI_CHSTAT_EOT) < 0) dev_err(&spi->dev, "EOT timed out\n"); + + /* disable chan to purge rx datas received in TX_ONLY transfer, + * otherwise these rx datas will affect the direct following + * RX_ONLY transfer. + */ + omap2_mcspi_set_enable(spi, 0); } out: omap2_mcspi_set_enable(spi, 1); -- 1.5.6.5 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
