Re: [PATCH] serial: msm: Unify TX and RX DMA paths

[neil.armstrong@linaro.org]

Hi Marek,

On 23/04/2024 14:08, Marek Szyprowski wrote:
> Use scatterlist-based API also for RX mode to unify TX and RX DMA paths
> as well as simplify the whole driver code a bit.

Thanks for the patch, I have no idea if this is right or wrong.

Greg, I think we should wait until this change is fully tested on multiple
platforms including DMA usage (bluetooth) before aplying it.

Thanks,
Neil

> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>   drivers/tty/serial/msm_serial.c | 86 +++++++++++++--------------------
>   1 file changed, 34 insertions(+), 52 deletions(-)
> 
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index 0a9c5219df88..d5e00e613f73 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -161,14 +161,8 @@ enum {
>   struct msm_dma {
>   	struct dma_chan		*chan;
>   	enum dma_data_direction dir;
> -	union {
> -		struct {
> -			dma_addr_t		phys;
> -			unsigned char		*virt;
> -			unsigned int		count;
> -		} rx;
> -		struct scatterlist tx_sg;
> -	};
> +	unsigned char		*virt;
> +	struct scatterlist	sg;
>   	dma_cookie_t		cookie;
>   	u32			enable_bit;
>   	struct dma_async_tx_descriptor	*desc;
> @@ -254,13 +248,7 @@ static void msm_stop_dma(struct uart_port *port, struct msm_dma *dma)
>   	unsigned int mapped;
>   	u32 val;
>   
> -	if (dma->dir == DMA_TO_DEVICE) {
> -		mapped = sg_dma_len(&dma->tx_sg);
> -	} else {
> -		mapped = dma->rx.count;
> -		dma->rx.count = 0;
> -	}
> -
> +	mapped = sg_dma_len(&dma->sg);
>   	dmaengine_terminate_all(dma->chan);
>   
>   	/*
> @@ -275,11 +263,8 @@ static void msm_stop_dma(struct uart_port *port, struct msm_dma *dma)
>   	msm_write(port, val, UARTDM_DMEN);
>   
>   	if (mapped) {
> -		if (dma->dir == DMA_TO_DEVICE) {
> -			dma_unmap_sg(dev, &dma->tx_sg, 1, dma->dir);
> -			sg_init_table(&dma->tx_sg, 1);
> -		} else
> -			dma_unmap_single(dev, dma->rx.phys, mapped, dma->dir);
> +		dma_unmap_sg(dev, &dma->sg, 1, dma->dir);
> +		sg_init_table(&dma->sg, 1);
>   	}
>   }
>   
> @@ -299,7 +284,7 @@ static void msm_release_dma(struct msm_port *msm_port)
>   	if (dma->chan) {
>   		msm_stop_dma(&msm_port->uart, dma);
>   		dma_release_channel(dma->chan);
> -		kfree(dma->rx.virt);
> +		kfree(dma->virt);
>   	}
>   
>   	memset(dma, 0, sizeof(*dma));
> @@ -371,8 +356,8 @@ static void msm_request_rx_dma(struct msm_port *msm_port, resource_size_t base)
>   
>   	of_property_read_u32(dev->of_node, "qcom,rx-crci", &crci);
>   
> -	dma->rx.virt = kzalloc(UARTDM_RX_SIZE, GFP_KERNEL);
> -	if (!dma->rx.virt)
> +	dma->virt = kzalloc(UARTDM_RX_SIZE, GFP_KERNEL);
> +	if (!dma->virt)
>   		goto rel_rx;
>   
>   	memset(&conf, 0, sizeof(conf));
> @@ -399,7 +384,7 @@ static void msm_request_rx_dma(struct msm_port *msm_port, resource_size_t base)
>   
>   	return;
>   err:
> -	kfree(dma->rx.virt);
> +	kfree(dma->virt);
>   rel_rx:
>   	dma_release_channel(dma->chan);
>   no_rx:
> @@ -434,7 +419,7 @@ static void msm_start_tx(struct uart_port *port)
>   	struct msm_dma *dma = &msm_port->tx_dma;
>   
>   	/* Already started in DMA mode */
> -	if (sg_dma_len(&dma->tx_sg))
> +	if (sg_dma_len(&dma->sg))
>   		return;
>   
>   	msm_port->imr |= MSM_UART_IMR_TXLEV;
> @@ -462,12 +447,12 @@ static void msm_complete_tx_dma(void *args)
>   	uart_port_lock_irqsave(port, &flags);
>   
>   	/* Already stopped */
> -	if (!sg_dma_len(&dma->tx_sg))
> +	if (!sg_dma_len(&dma->sg))
>   		goto done;
>   
>   	dmaengine_tx_status(dma->chan, dma->cookie, &state);
>   
> -	dma_unmap_sg(port->dev, &dma->tx_sg, 1, dma->dir);
> +	dma_unmap_sg(port->dev, &dma->sg, 1, dma->dir);
>   
>   	val = msm_read(port, UARTDM_DMEN);
>   	val &= ~dma->enable_bit;
> @@ -478,9 +463,9 @@ static void msm_complete_tx_dma(void *args)
>   		msm_write(port, MSM_UART_CR_TX_ENABLE, MSM_UART_CR);
>   	}
>   
> -	count = sg_dma_len(&dma->tx_sg) - state.residue;
> +	count = sg_dma_len(&dma->sg) - state.residue;
>   	uart_xmit_advance(port, count);
> -	sg_init_table(&dma->tx_sg, 1);
> +	sg_init_table(&dma->sg, 1);
>   
>   	/* Restore "Tx FIFO below watermark" interrupt */
>   	msm_port->imr |= MSM_UART_IMR_TXLEV;
> @@ -503,16 +488,16 @@ static int msm_handle_tx_dma(struct msm_port *msm_port, unsigned int count)
>   	int ret;
>   	u32 val;
>   
> -	sg_init_table(&dma->tx_sg, 1);
> -	kfifo_dma_out_prepare(&tport->xmit_fifo, &dma->tx_sg, 1, count);
> +	sg_init_table(&dma->sg, 1);
> +	kfifo_dma_out_prepare(&tport->xmit_fifo, &dma->sg, 1, count);
>   
> -	mapped = dma_map_sg(port->dev, &dma->tx_sg, 1, dma->dir);
> +	mapped = dma_map_sg(port->dev, &dma->sg, 1, dma->dir);
>   	if (!mapped) {
>   		ret = -EIO;
>   		goto zero_sg;
>   	}
>   
> -	dma->desc = dmaengine_prep_slave_sg(dma->chan, &dma->tx_sg, 1,
> +	dma->desc = dmaengine_prep_slave_sg(dma->chan, &dma->sg, 1,
>   						DMA_MEM_TO_DEV,
>   						DMA_PREP_INTERRUPT |
>   						DMA_PREP_FENCE);
> @@ -550,9 +535,9 @@ static int msm_handle_tx_dma(struct msm_port *msm_port, unsigned int count)
>   	dma_async_issue_pending(dma->chan);
>   	return 0;
>   unmap:
> -	dma_unmap_sg(port->dev, &dma->tx_sg, 1, dma->dir);
> +	dma_unmap_sg(port->dev, &dma->sg, 1, dma->dir);
>   zero_sg:
> -	sg_init_table(&dma->tx_sg, 1);
> +	sg_init_table(&dma->sg, 1);
>   	return ret;
>   }
>   
> @@ -569,7 +554,7 @@ static void msm_complete_rx_dma(void *args)
>   	uart_port_lock_irqsave(port, &flags);
>   
>   	/* Already stopped */
> -	if (!dma->rx.count)
> +	if (!sg_dma_len(&dma->sg))
>   		goto done;
>   
>   	val = msm_read(port, UARTDM_DMEN);
> @@ -586,14 +571,13 @@ static void msm_complete_rx_dma(void *args)
>   
>   	port->icount.rx += count;
>   
> -	dma->rx.count = 0;
> -
> -	dma_unmap_single(port->dev, dma->rx.phys, UARTDM_RX_SIZE, dma->dir);
> +	dma_unmap_sg(port->dev, &dma->sg, 1, dma->dir);
> +	sg_init_table(&dma->sg, 1);
>   
>   	for (i = 0; i < count; i++) {
>   		char flag = TTY_NORMAL;
>   
> -		if (msm_port->break_detected && dma->rx.virt[i] == 0) {
> +		if (msm_port->break_detected && dma->virt[i] == 0) {
>   			port->icount.brk++;
>   			flag = TTY_BREAK;
>   			msm_port->break_detected = false;
> @@ -604,9 +588,9 @@ static void msm_complete_rx_dma(void *args)
>   		if (!(port->read_status_mask & MSM_UART_SR_RX_BREAK))
>   			flag = TTY_NORMAL;
>   
> -		sysrq = uart_prepare_sysrq_char(port, dma->rx.virt[i]);
> +		sysrq = uart_prepare_sysrq_char(port, dma->virt[i]);
>   		if (!sysrq)
> -			tty_insert_flip_char(tport, dma->rx.virt[i], flag);
> +			tty_insert_flip_char(tport, dma->virt[i], flag);
>   	}
>   
>   	msm_start_rx_dma(msm_port);
> @@ -630,14 +614,13 @@ static void msm_start_rx_dma(struct msm_port *msm_port)
>   	if (!dma->chan)
>   		return;
>   
> -	dma->rx.phys = dma_map_single(uart->dev, dma->rx.virt,
> -				   UARTDM_RX_SIZE, dma->dir);
> -	ret = dma_mapping_error(uart->dev, dma->rx.phys);
> -	if (ret)
> +	sg_init_one(&dma->sg, dma->virt, UARTDM_RX_SIZE);
> +	ret = dma_map_sg(uart->dev, &dma->sg, 1, dma->dir);
> +	if (!ret)
>   		goto sw_mode;
>   
> -	dma->desc = dmaengine_prep_slave_single(dma->chan, dma->rx.phys,
> -						UARTDM_RX_SIZE, DMA_DEV_TO_MEM,
> +	dma->desc = dmaengine_prep_slave_sg(dma->chan, &dma->sg, 1,
> +						DMA_DEV_TO_MEM,
>   						DMA_PREP_INTERRUPT);
>   	if (!dma->desc)
>   		goto unmap;
> @@ -664,8 +647,6 @@ static void msm_start_rx_dma(struct msm_port *msm_port)
>   
>   	msm_write(uart, msm_port->imr, MSM_UART_IMR);
>   
> -	dma->rx.count = UARTDM_RX_SIZE;
> -
>   	dma_async_issue_pending(dma->chan);
>   
>   	msm_write(uart, MSM_UART_CR_CMD_RESET_STALE_INT, MSM_UART_CR);
> @@ -684,7 +665,8 @@ static void msm_start_rx_dma(struct msm_port *msm_port)
>   
>   	return;
>   unmap:
> -	dma_unmap_single(uart->dev, dma->rx.phys, UARTDM_RX_SIZE, dma->dir);
> +	dma_unmap_sg(uart->dev, &dma->sg, 1, dma->dir);
> +	sg_init_table(&dma->sg, 1);
>   
>   sw_mode:
>   	/*
> @@ -967,7 +949,7 @@ static irqreturn_t msm_uart_irq(int irq, void *dev_id)
>   	}
>   
>   	if (misr & (MSM_UART_IMR_RXLEV | MSM_UART_IMR_RXSTALE)) {
> -		if (dma->rx.count) {
> +		if (sg_dma_len(&dma->sg)) {
>   			val = MSM_UART_CR_CMD_STALE_EVENT_DISABLE;
>   			msm_write(port, val, MSM_UART_CR);
>   			val = MSM_UART_CR_CMD_RESET_STALE_INT;