From: Lukas Wunner lukas@wunner.de
commit 8d8bef50365847134b51c1ec46786bc2873e4e47 upstream.
Commit 6935224da248 ("spi: bcm2835: enable support of 3-wire mode") added 3-wire support to the BCM2835 SPI driver by setting the REN bit (Read Enable) in the CS register when receiving data. The REN bit puts the transmitter in high-impedance state. The driver recognizes that data is to be received by checking whether the rx_buf of a transfer is non-NULL.
Commit 3ecd37edaa2a ("spi: bcm2835: enable dma modes for transfers meeting certain conditions") subsequently broke 3-wire support because it set the SPI_MASTER_MUST_RX flag which causes spi_map_msg() to replace rx_buf with a dummy buffer if it is NULL. As a result, rx_buf is *always* non-NULL if DMA is enabled.
Reinstate 3-wire support by not only checking whether rx_buf is non-NULL, but also checking that it is not the dummy buffer.
Fixes: 3ecd37edaa2a ("spi: bcm2835: enable dma modes for transfers meeting certain conditions") Reported-by: Nuno Sá nuno.sa@analog.com Signed-off-by: Lukas Wunner lukas@wunner.de Cc: stable@vger.kernel.org # v4.2+ Cc: Martin Sperl kernel@martin.sperl.org Acked-by: Stefan Wahren wahrenst@gmx.net Link: https://lore.kernel.org/r/328318841455e505370ef8ecad97b646c033dc8a.156214852... Signed-off-by: Mark Brown broonie@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/spi/spi-bcm2835.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -764,7 +764,8 @@ static int bcm2835_spi_transfer_one(stru bcm2835_wr(bs, BCM2835_SPI_CLK, cdiv);
/* handle all the 3-wire mode */ - if ((spi->mode & SPI_3WIRE) && (tfr->rx_buf)) + if (spi->mode & SPI_3WIRE && tfr->rx_buf && + tfr->rx_buf != master->dummy_rx) cs |= BCM2835_SPI_CS_REN; else cs &= ~BCM2835_SPI_CS_REN;