linux-kernel - Re: [PATCH v2] serial: tegra: Read DMA status before terminating

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Date:   Wed, 19 Oct 2022 10:48:34 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Kartik <kkartik@...dia.com>, ldewangan@...dia.com,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        thierry.reding@...il.com, alan@...ux.intel.com, swarren@...dia.com,
        akhilrajeev@...dia.com, linux-serial@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] serial: tegra: Read DMA status before terminating


On 18/10/2022 15:58, Kartik wrote:
> Read the DMA status before terminating the DMA, as doing so deletes
> the DMA desc.
> 
> Also, to get the correct transfer status information, pause the DMA
> using dmaengine_pause() before reading the DMA status.
> 
> Fixes: e9ea096dd225 ("serial: tegra: add serial driver")
> 
> Signed-off-by: Akhil R <akhilrajeev@...dia.com>
> Signed-off-by: Kartik <kkartik@...dia.com>
> ---
> v1->v2:
>   * Pause the DMA before reading the DMA status.
>   * Updated commit message.
> 
>   drivers/tty/serial/serial-tegra.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
> index b7170cb9a544..cda9cd4fa92c 100644
> --- a/drivers/tty/serial/serial-tegra.c
> +++ b/drivers/tty/serial/serial-tegra.c
> @@ -619,8 +619,9 @@ static void tegra_uart_stop_tx(struct uart_port *u)
>   	if (tup->tx_in_progress != TEGRA_UART_TX_DMA)
>   		return;
>   
> -	dmaengine_terminate_all(tup->tx_dma_chan);
> +	dmaengine_pause(tup->tx_dma_chan);
>   	dmaengine_tx_status(tup->tx_dma_chan, tup->tx_cookie, &state);
> +	dmaengine_terminate_all(tup->tx_dma_chan);
>   	count = tup->tx_bytes_requested - state.residue;
>   	async_tx_ack(tup->tx_dma_desc);
>   	uart_xmit_advance(&tup->uport, count);
> @@ -763,8 +764,9 @@ static void tegra_uart_terminate_rx_dma(struct tegra_uart_port *tup)
>   		return;
>   	}
>   
> -	dmaengine_terminate_all(tup->rx_dma_chan);
> +	dmaengine_pause(tup->rx_dma_chan);
>   	dmaengine_tx_status(tup->rx_dma_chan, tup->rx_cookie, &state);
> +	dmaengine_terminate_all(tup->rx_dma_chan);
>   
>   	tegra_uart_rx_buffer_push(tup, state.residue);
>   	tup->rx_dma_active = false;

Thanks!

Reviewed-by: Jon Hunter <jonathanh@...dia.com>

Jon

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