linux-kernel - Re: [PATCH 03/13] tty: serial: atmel: Call dma_async_issue

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Message-ID: <6e29ab5d-070e-0407-96ad-129eb82afc88@posteo.net>
Date:   Fri, 19 Nov 2021 16:04:49 +0000
From:   Richard Genoud <richard.genoud@...teo.net>
To:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        ludovic.desroches@...rochip.com, vkoul@...nel.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        Richard Genoud <richard.genoud@...il.com>
Cc:     nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
        mripard@...nel.org, linux-arm-kernel@...ts.infradead.org,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH 03/13] tty: serial: atmel: Call dma_async_issue_pending()

Hi,

Le 16/11/2021 à 12:20, Tudor Ambarus a écrit :
> The driver wrongly assummed that tx_submit() will start the transfer,
> which is not the case, now that the at_xdmac driver is fixed. tx_submit
> is supposed to push the current transaction descriptor to a pending queue,
> waiting for issue_pending to be called. issue_pending must start the
> transfer, not tx_submit. While touching atmel_prepare_rx_dma(), introduce
> a local variable for the RX dma channel.
> 
> Fixes: 34df42f59a60 ("serial: at91: add rx dma support")
> Fixes: 08f738be88bb ("serial: at91: add tx dma support")
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> ---
>  drivers/tty/serial/atmel_serial.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 376f7a9c2868..b3e593f3c17f 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -1009,6 +1009,8 @@ static void atmel_tx_dma(struct uart_port *port)
>  				atmel_port->cookie_tx);
>  			return;
>  		}
> +
> +		dma_async_issue_pending(chan);
>  	}
>  
>  	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)

>From this hunk...
> @@ -1191,6 +1193,7 @@ static void atmel_rx_from_dma(struct uart_port *port)
>  static int atmel_prepare_rx_dma(struct uart_port *port)
>  {
>  	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
> +	struct dma_chan *chan_rx;
>  	struct device *mfd_dev = port->dev->parent;
>  	struct dma_async_tx_descriptor *desc;
>  	dma_cap_mask_t		mask;
> @@ -1203,11 +1206,13 @@ static int atmel_prepare_rx_dma(struct uart_port *port)
>  	dma_cap_zero(mask);
>  	dma_cap_set(DMA_CYCLIC, mask);
>  
> -	atmel_port->chan_rx = dma_request_slave_channel(mfd_dev, "rx");
> -	if (atmel_port->chan_rx == NULL)
> +	chan_rx = dma_request_slave_channel(mfd_dev, "rx");
> +	if (chan_rx == NULL)
>  		goto chan_err;
> +	atmel_port->chan_rx = chan_rx;
> +
>  	dev_info(port->dev, "using %s for rx DMA transfers\n",
> -		dma_chan_name(atmel_port->chan_rx));
> +		 dma_chan_name(chan_rx));
>  
>  	spin_lock_init(&atmel_port->lock_rx);
>  	sg_init_table(&atmel_port->sg_rx, 1);
> @@ -1239,8 +1244,7 @@ static int atmel_prepare_rx_dma(struct uart_port *port)
>  	config.src_addr = port->mapbase + ATMEL_US_RHR;
>  	config.src_maxburst = 1;
>  
> -	ret = dmaengine_slave_config(atmel_port->chan_rx,
> -				     &config);
> +	ret = dmaengine_slave_config(chan_rx, &config);
>  	if (ret) {
>  		dev_err(port->dev, "DMA rx slave configuration failed\n");
>  		goto chan_err;
> @@ -1249,7 +1253,7 @@ static int atmel_prepare_rx_dma(struct uart_port *port)
>  	 * Prepare a cyclic dma transfer, assign 2 descriptors,
>  	 * each one is half ring buffer size
>  	 */
> -	desc = dmaengine_prep_dma_cyclic(atmel_port->chan_rx,
> +	desc = dmaengine_prep_dma_cyclic(chan_rx,
>  					 sg_dma_address(&atmel_port->sg_rx),
>  					 sg_dma_len(&atmel_port->sg_rx),
>  					 sg_dma_len(&atmel_port->sg_rx)/2,
...to here :
I think this should go in another patch since these hunks only introduce "chan_rx".
And in this other patch, maybe add a little note on why "atmel_port->chan_rx = chan_rx;"
is after "chan_rx = dma_request_slave_channel(mfd_dev, "rx");"


> @@ -1269,12 +1273,14 @@ static int atmel_prepare_rx_dma(struct uart_port *port)
>  		goto chan_err;
>  	}
>  
> +	dma_async_issue_pending(chan_rx);
> +
>  	return 0;
>  
>  chan_err:
>  	dev_err(port->dev, "RX channel not available, switch to pio\n");
>  	atmel_port->use_dma_rx = false;
> -	if (atmel_port->chan_rx)
> +	if (chan_rx)
>  		atmel_release_rx_dma(port);
>  	return -EINVAL;
>  }
> 
The rest seems ok.

Thanks !

Richard.