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

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Date:	Thu, 9 Jun 2016 14:27:19 -0500
From:	Andy Gross <andy.gross@...aro.org>
To:	Charanya Venkatraman <charanya@...eaurora.org>
Cc:	agross@...eaurora.org, david.brown@...aro.org,
	gregkh@...uxfoundation.org, 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
Subject: Re: [PATCH v3] tty:serial:msm:Do not restore Rx interrupts in DMA

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@...eaurora.org>

Acked-by: Andy Gross <andy.gross@...aro.org>