Re: [PATCH v3] serial: samsung: use dma_ops of DMA if attached

[Krzysztof Kozlowski]

On 22/06/2021 11:17, Tamseel Shams wrote:
> When DMA is used for TX and RX by serial driver, it should
> pass the DMA device pointer to DMA API instead of UART device
> pointer. DMA device should be used for DMA API because only
> the DMA device is aware of how the device connects to the memory.
> There might be an extra level of address translation due to a
> SMMU attached to the DMA device. When serial device pointer device
> is used for DMA API, the DMA API will have no clue of the SMMU
> attached to the DMA device.
> 
> This patch is necessary to fix the SMMU page faults
> which is observed when a DMA(with SMMU enabled) is attached
> to UART for transfer.
> 
> Signed-off-by: Tamseel Shams <m.shams@xxxxxxxxxxx>
> Signed-off-by: Ajay Kumar <ajaykumar.rs@xxxxxxxxxxx>
> ---
> Changes since v1:
> 1. Rebased the patch on "tty-next" branch of TTY driver tree
> 
> Changes since v2:
> 1. Updated the commit message.
> 2. Changed the comment description
> 
>  drivers/tty/serial/samsung_tty.c | 62 +++++++++++++++++++++++++-------
>  1 file changed, 50 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> index 9fbc61151c2e..7dd648cb7237 100644
> --- a/drivers/tty/serial/samsung_tty.c
> +++ b/drivers/tty/serial/samsung_tty.c
> @@ -284,8 +284,13 @@ static void s3c24xx_serial_stop_tx(struct uart_port *port)
>  	struct s3c24xx_uart_dma *dma = ourport->dma;
>  	struct circ_buf *xmit = &port->state->xmit;
>  	struct dma_tx_state state;
> +	struct device *dma_map_ops_dev = ourport->port.dev;
>  	int count;
>  
> +	/* Null pointer check for "dma" and "dma->tx_chan" */

The comment is not useful.

> +	if (dma && dma->tx_chan)
> +		dma_map_ops_dev = dma->tx_chan->device->dev;
> +
>  	if (!ourport->tx_enabled)
>  		return;
>  
> @@ -305,7 +310,7 @@ static void s3c24xx_serial_stop_tx(struct uart_port *port)
>  		dmaengine_pause(dma->tx_chan);
>  		dmaengine_tx_status(dma->tx_chan, dma->tx_cookie, &state);
>  		dmaengine_terminate_all(dma->tx_chan);
> -		dma_sync_single_for_cpu(ourport->port.dev,
> +		dma_sync_single_for_cpu(dma_map_ops_dev,
>  			dma->tx_transfer_addr, dma->tx_size, DMA_TO_DEVICE);
>  		async_tx_ack(dma->tx_desc);
>  		count = dma->tx_bytes_requested - state.residue;
> @@ -331,14 +336,19 @@ static void s3c24xx_serial_tx_dma_complete(void *args)
>  	struct circ_buf *xmit = &port->state->xmit;
>  	struct s3c24xx_uart_dma *dma = ourport->dma;
>  	struct dma_tx_state state;
> +	struct device *dma_map_ops_dev = ourport->port.dev;
>  	unsigned long flags;
>  	int count;
>  
> +	/* Null pointer check for "dma" and "dma->tx_chan" */
> +	if (dma && dma->tx_chan)


What is the "else" here? How is it even possible? Why having this "if"
at all?

> +		dma_map_ops_dev = dma->tx_chan->device->dev;
> +
>  	dmaengine_tx_status(dma->tx_chan, dma->tx_cookie, &state);
>  	count = dma->tx_bytes_requested - state.residue;
>  	async_tx_ack(dma->tx_desc);
>  
> -	dma_sync_single_for_cpu(ourport->port.dev, dma->tx_transfer_addr,
> +	dma_sync_single_for_cpu(dma_map_ops_dev, dma->tx_transfer_addr,
>  				dma->tx_size, DMA_TO_DEVICE);
>  
>  	spin_lock_irqsave(&port->lock, flags);
> @@ -436,6 +446,11 @@ static int s3c24xx_serial_start_tx_dma(struct s3c24xx_uart_port *ourport,
>  	struct uart_port *port = &ourport->port;
>  	struct circ_buf *xmit = &port->state->xmit;
>  	struct s3c24xx_uart_dma *dma = ourport->dma;
> +	struct device *dma_map_ops_dev = ourport->port.dev;
> +
> +	/* Null pointer check for "dma" and "dma->tx_chan" */
> +	if (dma && dma->tx_chan)
> +		dma_map_ops_dev = dma->tx_chan->device->dev;
>  
>  	if (ourport->tx_mode != S3C24XX_TX_DMA)
>  		enable_tx_dma(ourport);
> @@ -443,7 +458,7 @@ static int s3c24xx_serial_start_tx_dma(struct s3c24xx_uart_port *ourport,
>  	dma->tx_size = count & ~(dma_get_cache_alignment() - 1);
>  	dma->tx_transfer_addr = dma->tx_addr + xmit->tail;
>  
> -	dma_sync_single_for_device(ourport->port.dev, dma->tx_transfer_addr,
> +	dma_sync_single_for_device(dma_map_ops_dev, dma->tx_transfer_addr,
>  				dma->tx_size, DMA_TO_DEVICE);
>  
>  	dma->tx_desc = dmaengine_prep_slave_single(dma->tx_chan,
> @@ -510,12 +525,17 @@ static void s3c24xx_uart_copy_rx_to_tty(struct s3c24xx_uart_port *ourport,
>  		struct tty_port *tty, int count)
>  {
>  	struct s3c24xx_uart_dma *dma = ourport->dma;
> +	struct device *dma_map_ops_dev = ourport->port.dev;
>  	int copied;
>  
> +	/* Null pointer check for "dma" and "dma->rx_chan" */
> +	if (dma && dma->rx_chan)
> +		dma_map_ops_dev = dma->rx_chan->device->dev;
> +
>  	if (!count)
>  		return;
>  
> -	dma_sync_single_for_cpu(ourport->port.dev, dma->rx_addr,
> +	dma_sync_single_for_cpu(dma_map_ops_dev, dma->rx_addr,
>  				dma->rx_size, DMA_FROM_DEVICE);
>  
>  	ourport->port.icount.rx += count;
> @@ -635,8 +655,13 @@ static void s3c24xx_serial_rx_dma_complete(void *args)
>  static void s3c64xx_start_rx_dma(struct s3c24xx_uart_port *ourport)
>  {
>  	struct s3c24xx_uart_dma *dma = ourport->dma;
> +	struct device *dma_map_ops_dev = ourport->port.dev;
> +
> +	/* Null pointer check for "dma" and "dma->rx_chan" */
> +	if (dma && dma->rx_chan)
> +		dma_map_ops_dev = dma->rx_chan->device->dev;
>  
> -	dma_sync_single_for_device(ourport->port.dev, dma->rx_addr,
> +	dma_sync_single_for_device(dma_map_ops_dev, dma->rx_addr,
>  				dma->rx_size, DMA_FROM_DEVICE);
>  
>  	dma->rx_desc = dmaengine_prep_slave_single(dma->rx_chan,
> @@ -1045,6 +1070,7 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
>  	struct s3c24xx_uart_dma	*dma = p->dma;
>  	struct dma_slave_caps dma_caps;
>  	const char *reason = NULL;
> +	struct device *dma_map_ops_dev = p->port.dev;
>  	int ret;
>  
>  	/* Default slave configuration parameters */
> @@ -1102,18 +1128,25 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
>  		goto err_release_tx;
>  	}
>  
> -	dma->rx_addr = dma_map_single(p->port.dev, dma->rx_buf,
> +	/* Null pointer check for "dma" and "dma->rx_chan" */
> +	if (dma && dma->rx_chan)
> +		dma_map_ops_dev = dma->rx_chan->device->dev;
> +
> +	dma->rx_addr = dma_map_single(dma_map_ops_dev, dma->rx_buf,
>  				dma->rx_size, DMA_FROM_DEVICE);
> -	if (dma_mapping_error(p->port.dev, dma->rx_addr)) {
> +	if (dma_mapping_error(dma_map_ops_dev, dma->rx_addr)) {
>  		reason = "DMA mapping error for RX buffer";
>  		ret = -EIO;
>  		goto err_free_rx;
>  	}
>  
> +	/* Null pointer check for "dma" and "dma->tx_chan" */
> +	if (dma && dma->tx_chan)
> +		dma_map_ops_dev = dma->tx_chan->device->dev;
>  	/* TX buffer */
> -	dma->tx_addr = dma_map_single(p->port.dev, p->port.state->xmit.buf,
> +	dma->tx_addr = dma_map_single(dma_map_ops_dev, p->port.state->xmit.buf,
>  				UART_XMIT_SIZE, DMA_TO_DEVICE);
> -	if (dma_mapping_error(p->port.dev, dma->tx_addr)) {
> +	if (dma_mapping_error(dma_map_ops_dev, dma->tx_addr)) {
>  		reason = "DMA mapping error for TX buffer";
>  		ret = -EIO;
>  		goto err_unmap_rx;
> @@ -1122,7 +1155,9 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
>  	return 0;
>  
>  err_unmap_rx:
> -	dma_unmap_single(p->port.dev, dma->rx_addr, dma->rx_size,
> +	if (dma->rx_chan)
> +		dma_map_ops_dev = dma->rx_chan->device->dev;
> +	dma_unmap_single(dma_map_ops_dev, dma->rx_addr, dma->rx_size,
>  			 DMA_FROM_DEVICE);
>  err_free_rx:
>  	kfree(dma->rx_buf);
> @@ -1139,10 +1174,12 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
>  static void s3c24xx_serial_release_dma(struct s3c24xx_uart_port *p)
>  {
>  	struct s3c24xx_uart_dma	*dma = p->dma;
> +	struct device *dma_map_ops_dev = p->port.dev;
>  
>  	if (dma->rx_chan) {
> +		dma_map_ops_dev = dma->rx_chan->device->dev;
>  		dmaengine_terminate_all(dma->rx_chan);
> -		dma_unmap_single(p->port.dev, dma->rx_addr,
> +		dma_unmap_single(dma_map_ops_dev, dma->rx_addr,
>  				dma->rx_size, DMA_FROM_DEVICE);
>  		kfree(dma->rx_buf);
>  		dma_release_channel(dma->rx_chan);
> @@ -1150,8 +1187,9 @@ static void s3c24xx_serial_release_dma(struct s3c24xx_uart_port *p)
>  	}
>  
>  	if (dma->tx_chan) {
> +		dma_map_ops_dev = dma->tx_chan->device->dev;
>  		dmaengine_terminate_all(dma->tx_chan);
> -		dma_unmap_single(p->port.dev, dma->tx_addr,
> +		dma_unmap_single(dma_map_ops_dev, dma->tx_addr,
>  				UART_XMIT_SIZE, DMA_TO_DEVICE);
>  		dma_release_channel(dma->tx_chan);
>  		dma->tx_chan = NULL;
> 


Best regards,
Krzysztof