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serial: 8250: omap: Disable DMA for console UART

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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Vignesh R 2017-04-22 18:37:19 +05:30 committed by Greg Kroah-Hartman
parent 2ea659a9ef
commit 84b40e3b57
1 changed files with 4 additions and 0 deletions
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4
drivers/tty/serial/8250/8250_omap.c
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@ -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) {