From: Tomoya MORINAGA <tomoya.rohm@xxxxxxxxx> Changing UART mode PIO->DMA->PIO->DMA like below, pch_uart driver can't get DMA channel resource. setserial /dev/ttyPCH0 ^low_latency setserial /dev/ttyPCH0 low_latency CAUSE: Changing mode using setserial command, ".startup" function which gets DMA channel is called before ".verify_port" function which sets dma-flag(use_dma/use_dma_flag) as 1. PIO->DMA .startup: Since dma-flag is 0, DMA channel is not requested. .verify_port: dma-flag is set as 1. .shutdown: N/A DMA->PIO .startup: Since dma-flag is 1, DMA channel is requested. .verify_port: dma-flag is set as 0. .shutdown: Since dma-flag is 0, DMA channel is not released. This means DMA channel resource leak occurs. Next time, this driver can't get DMA channel resource forever. MODIFICATION: Currently, when release DMA channel resource, this driver checks dma-flag. However, this specification occurs the above issue. This driver must check whether dma_request_channel is executed or not. The values are saved in private data variable "chan_tx/chan_tx". These variables mean if the value is NULL, DMA channel is not requested, if not NULL, DMA channel is requested. This patch fixes the issue. Signed-off-by: Tomoya MORINAGA <tomoya.rohm@xxxxxxxxx> Acked-by: Alan Cox <alan@xxxxxxxxxxxxxxx> Cc: stable <stable@xxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx> --- drivers/tty/serial/pch_uart.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c index ac852b5..d6aba8c 100644 --- a/drivers/tty/serial/pch_uart.c +++ b/drivers/tty/serial/pch_uart.c @@ -632,6 +632,7 @@ static void pch_request_dma(struct uart_port *port) dev_err(priv->port.dev, "%s:dma_request_channel FAILS(Rx)\n", __func__); dma_release_channel(priv->chan_tx); + priv->chan_tx = NULL; return; } @@ -1219,8 +1220,7 @@ static void pch_uart_shutdown(struct uart_port *port) dev_err(priv->port.dev, "pch_uart_hal_set_fifo Failed(ret=%d)\n", ret); - if (priv->use_dma_flag) - pch_free_dma(port); + pch_free_dma(port); free_irq(priv->port.irq, priv); } -- 1.7.7.3 -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
