[PATCH v2] tty:serial:msm:Do not restore Rx interrupts in DMA

From: Charanya Venkatraman
Date: Fri Jun 03 2016 - 07:11:01 EST

From: Charanya <charanya@xxxxxxxxxxxxxx>

Avoid data corruption issues that result in
CRC erros during file transfers over serial ports
at higher baud rates.

The current msm_serial driver masks the FIFO Rx
interrupts in msm_start_rx_dma() since Rx FIFO
interrupts are not required in DMA mode. However,
msm_complete_rx_dma() renables the Rx FIFO interrupt
which could cause RXSTALE event to be processed
when a TXLEV interrupt occurs.

The following is the sequence of events that
could occur resulting in data corruption

msm_start_rx_dma -> msm_complete_rx_dma -->
spin_unlock_irqrestore(&port->lock) --> msm_uart_irq()
(For TXLEV interrupt) --> msm_handle_rx_dm() (Read
from FIFO resulting in data corruption)

The patch fixes the issue by not restoring the RXLEV
and RXSTALE interrupts in msm_complete_rx_dma(). These
interrupts are required only in FIFO mode.

Signed-off-by: Charanya Venkatraman <charanya@xxxxxxxxxxxxxx>
drivers/tty/serial/msm_serial.c | 4 ----
1 file changed, 4 deletions(-)

diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
index b7d80bd..646aa3f 100644
--- a/drivers/tty/serial/msm_serial.c
+++ b/drivers/tty/serial/msm_serial.c
@@ -388,10 +388,6 @@ static void msm_complete_rx_dma(void *args)
val &= ~dma->enable_bit;
msm_write(port, val, UARTDM_DMEN);

- /* Restore interrupts */
- msm_port->imr |= UART_IMR_RXLEV | UART_IMR_RXSTALE;
- msm_write(port, msm_port->imr, UART_IMR);
if (msm_read(port, UART_SR) & UART_SR_OVERRUN) {
tty_insert_flip_char(tport, 0, TTY_OVERRUN);
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