linux-kernel - Re: [PATCH] tty: serial: fsl_lpuart: Fix Tx DMA edge case

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Date:   Mon, 10 Oct 2016 16:42:13 +0530
From:   Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>
To:     Aaron Brice <aaron.brice@...asoft.com>,
        <gregkh@...uxfoundation.org>, <jslaby@...e.com>, <stefan@...er.ch>
CC:     <linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] tty: serial: fsl_lpuart: Fix Tx DMA edge case

On 10/07/16 03:43, Aaron Brice wrote:

> In the case where head == 0 on the circular buffer, there should be one
> DMA buffer, not two.  The second zero-length buffer would break the
> lpuart driver, transfer would never complete.

Tested-by: Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>

>
> Signed-off-by: Aaron Brice <aaron.brice@...asoft.com>
> ---
>   drivers/tty/serial/fsl_lpuart.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
> index de9d510..76103f2 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -328,7 +328,7 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
>   
>   	sport->dma_tx_bytes = uart_circ_chars_pending(xmit);
>   
> -	if (xmit->tail < xmit->head) {
> +	if (xmit->tail < xmit->head || xmit->head == 0) {
>   		sport->dma_tx_nents = 1;
>   		sg_init_one(sgl, xmit->buf + xmit->tail, sport->dma_tx_bytes);
>   	} else {
> @@ -359,7 +359,6 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
>   	sport->dma_tx_in_progress = true;
>   	sport->dma_tx_cookie = dmaengine_submit(sport->dma_tx_desc);
>   	dma_async_issue_pending(sport->dma_tx_chan);
> -
>   }
>   
>   static void lpuart_dma_tx_complete(void *arg)