On Mon, 13 Jan 2020 at 20:53, Jeffrey Hugo <jeffrey.l.hugo@xxxxxxxxx> wrote: > > 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? Yes, but the TX case is already handled. If msm_handle_tx_dma fails, msm_handle_tx_pio is used to directly write the FIFO. > > > > > 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? The DMEN clear occurs on DMA RX completion (msm_complete_tx_dma()) and set on DMA restart (msm_start_rx_dma). In our case, since DMA start fails, we just reset the RX path to effectively apply the SW/FIFO mode. > > > + * 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 > > Regards, Loic
