From 462af9d545e9d15f31c8173ae4df856f4e8a1171 Mon Sep 17 00:00:00 2001 From: Vignesh R Date: Sat, 22 Apr 2017 18:37:19 +0530 Subject: [PATCH] serial: 8250: omap: Disable DMA for console UART [ Upstream commit 84b40e3b57eef1417479c00490dd4c9f6e5ffdbc ] Kernel always writes log messages to console via serial8250_console_write()->serial8250_console_putchar() which directly accesses UART_TX register _without_ using DMA. But, if other processes like systemd using same UART port, then these writes are handled by a different code flow using 8250_omap driver where there is provision to use DMA. It seems that it is possible that both DMA and CPU might simultaneously put data to UART FIFO and lead to potential loss of data due to FIFO overflow and weird data corruption. This happens when both kernel console and userspace tries to write simultaneously to the same UART port. Therefore, disable DMA on kernel console port to avoid potential race between CPU and DMA. Signed-off-by: Vignesh R Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_omap.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c index e8dd296..c438357 100644 --- a/drivers/tty/serial/8250/8250_omap.c +++ b/drivers/tty/serial/8250/8250_omap.c @@ -608,6 +608,10 @@ static int omap_8250_startup(struct uart_port *port) up->lsr_saved_flags = 0; up->msr_saved_flags = 0; + /* Disable DMA for console UART */ + if (uart_console(port)) + up->dma = NULL; + if (up->dma) { ret = serial8250_request_dma(up); if (ret) { -- 2.7.4