Re: [PATCH 11/15] tty: msm_serial: use dmaengine_prep_slave_sg()

From: Marek Szyprowski
Date: Mon Apr 15 2024 - 17:17:33 EST

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On 05.04.2024 08:08, Jiri Slaby (SUSE) wrote:
> This is a preparatory for the serial-to-kfifo switch. kfifo understands
> only scatter-gatter approach, so switch to that.
>
> No functional change intended, it's just dmaengine_prep_slave_single()
> inline expanded.
>
> And in this case, switch from dma_map_single() to dma_map_sg() too. This
> needs struct msm_dma changes. I split the rx and tx parts into an union.
> TX is now struct scatterlist, RX remains the old good phys-virt-count
> triple.
>
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@xxxxxxxxxx>
> Cc: Bjorn Andersson <andersson@xxxxxxxxxx>
> Cc: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
> Cc: linux-arm-msm@xxxxxxxxxxxxxxx

I've just found that this patch broke UART operation on DragonBoard
410c. I briefly checked and didn't notice anything obviously wrong here,
but the board stops transmitting any data from its serial port after the
first message. I will try to analyze this issue a bit more tomorrow.

> ---
> drivers/tty/serial/msm_serial.c | 86 +++++++++++++++++++--------------
> 1 file changed, 49 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index d27c4c8c84e1..7bf30e632313 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -161,11 +161,16 @@ enum {
> struct msm_dma {
> struct dma_chan *chan;
> enum dma_data_direction dir;
> - dma_addr_t phys;
> - unsigned char *virt;
> + union {
> + struct {
> + dma_addr_t phys;
> + unsigned char *virt;
> + unsigned int count;
> + } rx;
> + struct scatterlist tx_sg;
> + };
> dma_cookie_t cookie;
> u32 enable_bit;
> - unsigned int count;
> struct dma_async_tx_descriptor *desc;
> };
>
> @@ -249,8 +254,12 @@ static void msm_stop_dma(struct uart_port *port, struct msm_dma *dma)
> unsigned int mapped;
> u32 val;
>
> - mapped = dma->count;
> - dma->count = 0;
> + if (dma->dir == DMA_TO_DEVICE) {
> + mapped = sg_dma_len(&dma->tx_sg);
> + } else {
> + mapped = dma->rx.count;
> + dma->rx.count = 0;
> + }
>
> dmaengine_terminate_all(dma->chan);
>
> @@ -265,8 +274,13 @@ static void msm_stop_dma(struct uart_port *port, struct msm_dma *dma)
> val &= ~dma->enable_bit;
> msm_write(port, val, UARTDM_DMEN);
>
> - if (mapped)
> - dma_unmap_single(dev, dma->phys, mapped, dma->dir);
> + 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);
> + }
> }
>
> static void msm_release_dma(struct msm_port *msm_port)
> @@ -285,7 +299,7 @@ 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->virt);
> + kfree(dma->rx.virt);
> }
>
> memset(dma, 0, sizeof(*dma));
> @@ -357,8 +371,8 @@ 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->virt = kzalloc(UARTDM_RX_SIZE, GFP_KERNEL);
> - if (!dma->virt)
> + dma->rx.virt = kzalloc(UARTDM_RX_SIZE, GFP_KERNEL);
> + if (!dma->rx.virt)
> goto rel_rx;
>
> memset(&conf, 0, sizeof(conf));
> @@ -385,7 +399,7 @@ static void msm_request_rx_dma(struct msm_port *msm_port, resource_size_t base)
>
> return;
> err:
> - kfree(dma->virt);
> + kfree(dma->rx.virt);
> rel_rx:
> dma_release_channel(dma->chan);
> no_rx:
> @@ -420,7 +434,7 @@ static void msm_start_tx(struct uart_port *port)
> struct msm_dma *dma = &msm_port->tx_dma;
>
> /* Already started in DMA mode */
> - if (dma->count)
> + if (sg_dma_len(&dma->tx_sg))
> return;
>
> msm_port->imr |= MSM_UART_IMR_TXLEV;
> @@ -448,12 +462,12 @@ static void msm_complete_tx_dma(void *args)
> uart_port_lock_irqsave(port, &flags);
>
> /* Already stopped */
> - if (!dma->count)
> + if (!sg_dma_len(&dma->tx_sg))
> goto done;
>
> dmaengine_tx_status(dma->chan, dma->cookie, &state);
>
> - dma_unmap_single(port->dev, dma->phys, dma->count, dma->dir);
> + dma_unmap_sg(port->dev, &dma->tx_sg, 1, dma->dir);
>
> val = msm_read(port, UARTDM_DMEN);
> val &= ~dma->enable_bit;
> @@ -464,9 +478,9 @@ static void msm_complete_tx_dma(void *args)
> msm_write(port, MSM_UART_CR_TX_ENABLE, MSM_UART_CR);
> }
>
> - count = dma->count - state.residue;
> + count = sg_dma_len(&dma->tx_sg) - state.residue;
> uart_xmit_advance(port, count);
> - dma->count = 0;
> + sg_init_table(&dma->tx_sg, 1);
>
> /* Restore "Tx FIFO below watermark" interrupt */
> msm_port->imr |= MSM_UART_IMR_TXLEV;
> @@ -485,19 +499,18 @@ static int msm_handle_tx_dma(struct msm_port *msm_port, unsigned int count)
> struct circ_buf *xmit = &msm_port->uart.state->xmit;
> struct uart_port *port = &msm_port->uart;
> struct msm_dma *dma = &msm_port->tx_dma;
> - void *cpu_addr;
> int ret;
> u32 val;
>
> - cpu_addr = &xmit->buf[xmit->tail];
> + sg_init_table(&dma->tx_sg, 1);
> + sg_set_buf(&dma->tx_sg, &xmit->buf[xmit->tail], count);
>
> - dma->phys = dma_map_single(port->dev, cpu_addr, count, dma->dir);
> - ret = dma_mapping_error(port->dev, dma->phys);
> + ret = dma_map_sg(port->dev, &dma->tx_sg, 1, dma->dir);
> if (ret)
> return ret;
>
> - dma->desc = dmaengine_prep_slave_single(dma->chan, dma->phys,
> - count, DMA_MEM_TO_DEV,
> + dma->desc = dmaengine_prep_slave_sg(dma->chan, &dma->tx_sg, 1,
> + DMA_MEM_TO_DEV,
> DMA_PREP_INTERRUPT |
> DMA_PREP_FENCE);
> if (!dma->desc) {
> @@ -520,8 +533,6 @@ static int msm_handle_tx_dma(struct msm_port *msm_port, unsigned int count)
> msm_port->imr &= ~MSM_UART_IMR_TXLEV;
> msm_write(port, msm_port->imr, MSM_UART_IMR);
>
> - dma->count = count;
> -
> val = msm_read(port, UARTDM_DMEN);
> val |= dma->enable_bit;
>
> @@ -536,7 +547,8 @@ 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_single(port->dev, dma->phys, count, dma->dir);
> + dma_unmap_sg(port->dev, &dma->tx_sg, 1, dma->dir);
> + sg_init_table(&dma->tx_sg, 1);
> return ret;
> }
>
> @@ -553,7 +565,7 @@ static void msm_complete_rx_dma(void *args)
> uart_port_lock_irqsave(port, &flags);
>
> /* Already stopped */
> - if (!dma->count)
> + if (!dma->rx.count)
> goto done;
>
> val = msm_read(port, UARTDM_DMEN);
> @@ -570,14 +582,14 @@ static void msm_complete_rx_dma(void *args)
>
> port->icount.rx += count;
>
> - dma->count = 0;
> + dma->rx.count = 0;
>
> - dma_unmap_single(port->dev, dma->phys, UARTDM_RX_SIZE, dma->dir);
> + dma_unmap_single(port->dev, dma->rx.phys, UARTDM_RX_SIZE, dma->dir);
>
> for (i = 0; i < count; i++) {
> char flag = TTY_NORMAL;
>
> - if (msm_port->break_detected && dma->virt[i] == 0) {
> + if (msm_port->break_detected && dma->rx.virt[i] == 0) {
> port->icount.brk++;
> flag = TTY_BREAK;
> msm_port->break_detected = false;
> @@ -588,9 +600,9 @@ 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->virt[i]);
> + sysrq = uart_prepare_sysrq_char(port, dma->rx.virt[i]);
> if (!sysrq)
> - tty_insert_flip_char(tport, dma->virt[i], flag);
> + tty_insert_flip_char(tport, dma->rx.virt[i], flag);
> }
>
> msm_start_rx_dma(msm_port);
> @@ -614,13 +626,13 @@ static void msm_start_rx_dma(struct msm_port *msm_port)
> if (!dma->chan)
> return;
>
> - dma->phys = dma_map_single(uart->dev, dma->virt,
> + dma->rx.phys = dma_map_single(uart->dev, dma->rx.virt,
> UARTDM_RX_SIZE, dma->dir);
> - ret = dma_mapping_error(uart->dev, dma->phys);
> + ret = dma_mapping_error(uart->dev, dma->rx.phys);
> if (ret)
> goto sw_mode;
>
> - dma->desc = dmaengine_prep_slave_single(dma->chan, dma->phys,
> + dma->desc = dmaengine_prep_slave_single(dma->chan, dma->rx.phys,
> UARTDM_RX_SIZE, DMA_DEV_TO_MEM,
> DMA_PREP_INTERRUPT);
> if (!dma->desc)
> @@ -648,7 +660,7 @@ static void msm_start_rx_dma(struct msm_port *msm_port)
>
> msm_write(uart, msm_port->imr, MSM_UART_IMR);
>
> - dma->count = UARTDM_RX_SIZE;
> + dma->rx.count = UARTDM_RX_SIZE;
>
> dma_async_issue_pending(dma->chan);
>
> @@ -668,7 +680,7 @@ static void msm_start_rx_dma(struct msm_port *msm_port)
>
> return;
> unmap:
> - dma_unmap_single(uart->dev, dma->phys, UARTDM_RX_SIZE, dma->dir);
> + dma_unmap_single(uart->dev, dma->rx.phys, UARTDM_RX_SIZE, dma->dir);
>
> sw_mode:
> /*
> @@ -955,7 +967,7 @@ static irqreturn_t msm_uart_irq(int irq, void *dev_id)
> }
>
> if (misr & (MSM_UART_IMR_RXLEV | MSM_UART_IMR_RXSTALE)) {
> - if (dma->count) {
> + if (dma->rx.count) {
> val = MSM_UART_CR_CMD_STALE_EVENT_DISABLE;
> msm_write(port, val, MSM_UART_CR);
> val = MSM_UART_CR_CMD_RESET_STALE_INT;

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Next message: Vishal Moola (Oracle): "[PATCH] hugetlb: Check for anon_vma prior to folio allocation"
Previous message: Sean Christopherson: "Re: [PATCH v2 07/10] KVM: x86: Always populate L1 GPA for KVM_MAP_MEMORY"
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