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

[Krzysztof Kozlowski]

Hi,

Thanks for the patch.

On 21/06/2021 06:49, 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.

Hmmm, but why DMA device pointer should be used?

> 
> 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>
> ---
>  drivers/tty/serial/samsung_tty.c | 60 +++++++++++++++++++++++++-------
>  1 file changed, 48 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> index b923683e6a25..5bdc7dd2a5e2 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;
>  
> +	/* Pick dma_ops of DMA device if DMA device is attached */

You mention here and further comments "dma_ops". I don't see you
changing the DMA ops, but the device. It's quite confusing. I think you
meant a DMA device shall be passed to DMA API?

Second question: you write that DMA devices should be used if DMA is
attached and in the code you follow such pattern a lot:

> +	if (dma && dma->tx_chan)
> +		dma_map_ops_dev = dma->tx_chan->device->dev;
> +

Are you trying to say that if DMA is not attached, UART device should be
used? If DMA is not attached, how are the DMA operations used then?

>  	if (!ourport->tx_enabled)
>  		return;
>  
> @@ -298,7 +303,7 @@ 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;
> @@ -324,15 +329,19 @@ 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;
>  
> +	/* Pick dma_ops of DMA device if DMA device is attached */
> +	if (dma && dma->tx_chan)
> +		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);
> @@ -408,7 +417,11 @@ 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;
>  
> +	/* Pick dma_ops of DMA device if DMA device is attached */
> +	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);
> @@ -416,7 +429,7 @@ 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,
> @@ -483,12 +496,17 @@ 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;
>  
> +	/* Pick dma_ops of DMA device if DMA device is attached */
> +	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;
> @@ -600,8 +618,13 @@ 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;
>  
> -	dma_sync_single_for_device(ourport->port.dev, dma->rx_addr,
> +	/* Pick dma_ops of DMA device if DMA device is attached */
> +	if (dma && dma->rx_chan)
> +		dma_map_ops_dev = dma->rx_chan->device->dev;
> +
> +	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,
> @@ -983,6 +1006,7 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)

Offset of hunks looks here significantly different than mainline. The
patch should be based and tested mainline tree. Which one did you choose
as base?

Using my email address not from get_maintainers.pl also suggests that
you don't use anything recent as a base.

Best regards,
Krzysztof