[PATCH v3] tty:serial:msm:Do not restore Rx interrupts in DMA

[Andy Gross]

On Tue, Jun 07, 2016 at 03:58:41PM +0530, Charanya Venkatraman wrote:
> Avoid data corruption issues that result in CRC errors 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() re-enables the Rx FIFO interrupts
> 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 at codeaurora.org>

Acked-by: Andy Gross <andy.gross at linaro.org>