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

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Message-Id: <1465295321-10506-1-git-send-email-charanya@codeaurora.org>
Date:	Tue,  7 Jun 2016 15:58:41 +0530
From:	Charanya Venkatraman <charanya@...eaurora.org>
To:	agross@...eaurora.org, david.brown@...aro.org,
	andy.gross@...aro.org, gregkh@...uxfoundation.org
Cc:	jslaby@...e.com, linux-soc@...r.kernel.org,
	linux-serial@...r.kernel.org, sricharan@...eaurora.org,
	architt@...eaurora.org, linux-arm-msm@...r.kernel.org,
	ntelkar@...eaurora.org, galak@...eaurora.org,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, absahu@...eaurora.org,
	njaigane@...eaurora.org,
	Charanya Venkatraman <charanya@...eaurora.org>
Subject: [PATCH v3] tty:serial:msm:Do not restore Rx interrupts in DMA

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@...eaurora.org>
---
Changes in v2:
	- Make commit message more clearer.
Changes in v3:
	- Fix typos in commit message.

 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) {
 		port->icount.overrun++;
 		tty_insert_flip_char(tport, 0, TTY_OVERRUN);
-- 
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