On Fri, Jan 10, 2020 at 1:55 AM Loic Poulain <loic.poulain@xxxxxxxxxx> wrote: > > During db410c stress test and when the system is low on memory, > the UART/console becomes unresponsive and never recover back. > This has been narrowed down to the msm_start_rx_dma which does > not manage error cases correctly (e.g. dma mapping failure), > indeed, when an error happens, dma transfer is simply discarded > and so never completed, leading to unconfigured RX path. > > This patch fixes this issue by switching to SW/FIFO mode in case > of DMA issue. This mainly consists in resetting the receiver to > apply RX BAM/DMA disabling change and re-enabling the RX level > and stale interrupts (previously disabled for DMA transfers). > > The DMA will be re-enabled once memory is available since the > SW/FIFO read function (msm_handle_rx_dm) retries to start dma > on completion. Is there a risk of the same thing occurring in the TX path? > > Signed-off-by: Loic Poulain <loic.poulain@xxxxxxxxxx> > --- > drivers/tty/serial/msm_serial.c | 18 +++++++++++++++++- > 1 file changed, 17 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c > index 1cbae07..a63b703 100644 > --- a/drivers/tty/serial/msm_serial.c > +++ b/drivers/tty/serial/msm_serial.c > @@ -610,7 +610,7 @@ static void msm_start_rx_dma(struct msm_port *msm_port) > UARTDM_RX_SIZE, dma->dir); > ret = dma_mapping_error(uart->dev, dma->phys); > if (ret) > - return; > + goto sw_mode; > > dma->desc = dmaengine_prep_slave_single(dma->chan, dma->phys, > UARTDM_RX_SIZE, DMA_DEV_TO_MEM, > @@ -661,6 +661,22 @@ static void msm_start_rx_dma(struct msm_port *msm_port) > return; > unmap: > dma_unmap_single(uart->dev, dma->phys, UARTDM_RX_SIZE, dma->dir); > + > +sw_mode: > + /* > + * Switch from DMA to SW/FIFO mode. After clearing Rx BAM (UARTDM_DMEN), Where does this clear of UARTDM_DMEN occur? > + * receiver must be reset. > + */ > + msm_write(uart, UART_CR_CMD_RESET_RX, UART_CR); > + msm_write(uart, UART_CR_RX_ENABLE, UART_CR); > + > + msm_write(uart, UART_CR_CMD_RESET_STALE_INT, UART_CR); > + msm_write(uart, 0xFFFFFF, UARTDM_DMRX); > + msm_write(uart, UART_CR_CMD_STALE_EVENT_ENABLE, UART_CR); > + > + /* Re-enable RX interrupts */ > + msm_port->imr |= (UART_IMR_RXLEV | UART_IMR_RXSTALE); > + msm_write(uart, msm_port->imr, UART_IMR); > } > > static void msm_stop_rx(struct uart_port *port) > -- > 2.7.4 >
