linux-kernel - Re: [PATCH] serial: msm: check dma_map

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Date: Fri, 19 Apr 2024 11:03:35 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>, gregkh@...uxfoundation.org
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: msm: check dma_map_sg() return value properly

On 19.04.2024 10:09, Jiri Slaby (SUSE) wrote:
> The -next commit f8fef2fa419f (tty: msm_serial: use
> dmaengine_prep_slave_sg()), switched to using dma_map_sg(). But the
> return value of dma_map_sg() is special: it returns number of elements
> mapped. And not a standard error value.
>
> The commit also forgot to reset dma->tx_sg in case of this failure.
>
> Fix both these mistakes.
>
> Thanks to Marek who helped debugging this.
>
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

> ---
>   drivers/tty/serial/msm_serial.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index ae7a8e3cf467..0a9c5219df88 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -499,15 +499,18 @@ static int msm_handle_tx_dma(struct msm_port *msm_port, unsigned int count)
>   	struct uart_port *port = &msm_port->uart;
>   	struct tty_port *tport = &port->state->port;
>   	struct msm_dma *dma = &msm_port->tx_dma;
> +	unsigned int mapped;
>   	int ret;
>   	u32 val;
>   
>   	sg_init_table(&dma->tx_sg, 1);
>   	kfifo_dma_out_prepare(&tport->xmit_fifo, &dma->tx_sg, 1, count);
>   
> -	ret = dma_map_sg(port->dev, &dma->tx_sg, 1, dma->dir);
> -	if (ret)
> -		return ret;
> +	mapped = dma_map_sg(port->dev, &dma->tx_sg, 1, dma->dir);
> +	if (!mapped) {
> +		ret = -EIO;
> +		goto zero_sg;
> +	}
>   
>   	dma->desc = dmaengine_prep_slave_sg(dma->chan, &dma->tx_sg, 1,
>   						DMA_MEM_TO_DEV,
> @@ -548,6 +551,7 @@ static int msm_handle_tx_dma(struct msm_port *msm_port, unsigned int count)
>   	return 0;
>   unmap:
>   	dma_unmap_sg(port->dev, &dma->tx_sg, 1, dma->dir);
> +zero_sg:
>   	sg_init_table(&dma->tx_sg, 1);
>   	return ret;
>   }

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland