From: Uwe Kleine-König u.kleine-koenig@pengutronix.de
commit 1866541492641c02874bf51f9d8712b5510f2c64 upstream.
When using RS485 half duplex the Transmitter Complete irq is needed to determine the moment when the transmitter can be disabled. When using DMA this irq must only be enabled when DMA has completed to transfer all data. Otherwise the CPU might busily trigger this irq which is not properly handled and so the also pending irq for the DMA transfer cannot trigger.
Signed-off-by: Uwe Kleine-König u.kleine-koenig@pengutronix.de [Backport to v4.14] Signed-off-by: Frieder Schrempf frieder.schrempf@kontron.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/tty/serial/imx.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-)
--- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -538,6 +538,11 @@ static void dma_tx_callback(void *data)
if (!uart_circ_empty(xmit) && !uart_tx_stopped(&sport->port)) imx_dma_tx(sport); + else if (sport->port.rs485.flags & SER_RS485_ENABLED) { + temp = readl(sport->port.membase + UCR4); + temp |= UCR4_TCEN; + writel(temp, sport->port.membase + UCR4); + }
spin_unlock_irqrestore(&sport->port.lock, flags); } @@ -555,6 +560,10 @@ static void imx_dma_tx(struct imx_port * if (sport->dma_is_txing) return;
+ temp = readl(sport->port.membase + UCR4); + temp &= ~UCR4_TCEN; + writel(temp, sport->port.membase + UCR4); + sport->tx_bytes = uart_circ_chars_pending(xmit);
if (xmit->tail < xmit->head || xmit->head == 0) { @@ -617,10 +626,15 @@ static void imx_start_tx(struct uart_por if (!(port->rs485.flags & SER_RS485_RX_DURING_TX)) imx_stop_rx(port);
- /* enable transmitter and shifter empty irq */ - temp = readl(port->membase + UCR4); - temp |= UCR4_TCEN; - writel(temp, port->membase + UCR4); + /* + * Enable transmitter and shifter empty irq only if DMA is off. + * In the DMA case this is done in the tx-callback. + */ + if (!sport->dma_is_enabled) { + temp = readl(port->membase + UCR4); + temp |= UCR4_TCEN; + writel(temp, port->membase + UCR4); + } }
if (!sport->dma_is_enabled) {