| Message ID | 20170422130719.8366-1-vigneshr@ti.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c index e7e64913a748..d81bac98d190 100644 --- a/drivers/tty/serial/8250/8250_omap.c +++ b/drivers/tty/serial/8250/8250_omap.c @@ -613,6 +613,10 @@ 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) {
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 <vigneshr@ti.com> --- drivers/tty/serial/8250/8250_omap.c | 4 ++++ 1 file changed, 4 insertions(+)