RE: [PATCH v2] serial: samsung: use dma_ops of DMA if attached

["M Tamseel Shams" <m.shams@samsung.com>]

> On 2021-06-22 04:52, 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.
> >
> > 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@samsung.com>
> > Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
> > ---
> >   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..0c924bb6108e 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 */
> > +	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;
> >
> > +	/* Pick dma_ops of DMA device if DMA device is attached */
> > +	if (dma && dma->tx_chan)
> 
> Clearly you don't need most of these checks, if any. For example here you're
> already dereferencing dma->tx_chan unconditionally a couple of lines below.
> 
> AFAICS it should simply be a case of hard-coding the correct device for all of the
> DMA API calls without any of this silly conditional assignment. If it's even
> possible to reach the point of making a DMA API call when you don't have a valid
> DMA channel (and thus it would be pointless anyway), that implies a more
> general issue with the structure of the code which deserves fixing in its own
> right.
> 
> Robin.
> 
Yes, this looks like a perfect solution to remove the conditional assignments and
instead directly assign the DMA device pointer.

> > +		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;
> > +
> > +	/* 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);
> > @@ -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;
> >
> > +	/* 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;
> > @@ -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;
> > +
> > +	/* 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(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,
> > +	/* 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->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;
> >   	}
> >
> > +	/* 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;
> >   	/* 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;
> >

Thanks & Regards,
Tamseel Shams