Right now it is possible that serial8250_tx_dma() fails and returns
-EBUSY. The caller (serial8250_start_tx()) will then enable
UART_IER_THRI which will generate an interrupt once the TX FIFO is
empty.
In serial8250_handle_irq() nothing will happen because up->dma is set
and so serial8250_tx_chars() won't be invoked. We end up with plenty of
interrupts and some "too much work for irq" output.
This patch introduces dma_tx_err in struct uart_8250_port to signal that
the last invocation of serial8250_tx_dma() failed so we can fill the TX
FIFO manually. Should the next invocation of serial8250_start_tx()
succeed then the dma_tx_err flag along with the THRI bit is removed and
DMA only usage may continue.
Reviewed-by: Tony Lindgren <tony@xxxxxxxxxxx>
Tested-by: Tony Lindgren <tony@xxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250.h | 1 +
drivers/tty/serial/8250/8250_core.c | 4 +++-
drivers/tty/serial/8250/8250_dma.c | 30 +++++++++++++++++++++++++-----
3 files changed, 29 insertions(+), 6 deletions(-)
diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 1bcb4b2141a6..a63d198f8d03 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -41,6 +41,7 @@ struct uart_8250_dma {
size_t tx_size;
unsigned char tx_running:1;
+ unsigned char tx_err: 1;
};
struct old_serial_port {
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 139f3d2b8aa9..9f961ea82564 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -1594,8 +1594,10 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
status = serial8250_rx_chars(up, status);
}
serial8250_modem_status(up);
- if (!up->dma && (status & UART_LSR_THRE))
+ if ((!up->dma || (up->dma && up->dma->tx_err)) &&
+ (status & UART_LSR_THRE)) {
serial8250_tx_chars(up);
+ }
spin_unlock_irqrestore(&port->lock, flags);
return 1;
diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index 148ffe4c232f..69e54abb6e71 100644
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -36,8 +36,16 @@ static void __dma_tx_complete(void *param)
if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
uart_write_wakeup(&p->port);
- if (!uart_circ_empty(xmit) && !uart_tx_stopped(&p->port))
- serial8250_tx_dma(p);
+ if (!uart_circ_empty(xmit) && !uart_tx_stopped(&p->port)) {
+ int ret;
+
+ ret = serial8250_tx_dma(p);
+ if (ret) {
+ dma->tx_err = 1;
+ p->ier |= UART_IER_THRI;
+ serial_port_out(&p->port, UART_IER, p->ier);
+ }
+ }
spin_unlock_irqrestore(&p->port.lock, flags);
}
@@ -69,6 +77,7 @@ int serial8250_tx_dma(struct uart_8250_port *p)
struct uart_8250_dma *dma = p->dma;
struct circ_buf *xmit = &p->port.state->xmit;
struct dma_async_tx_descriptor *desc;
+ int ret;
if (uart_tx_stopped(&p->port) || dma->tx_running ||
uart_circ_empty(xmit))
@@ -80,8 +89,10 @@ int serial8250_tx_dma(struct uart_8250_port *p)
dma->tx_addr + xmit->tail,
dma->tx_size, DMA_MEM_TO_DEV,
DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
- if (!desc)
- return -EBUSY;
+ if (!desc) {
+ ret = -EBUSY;
+ goto err;
+ }
dma->tx_running = 1;
@@ -94,8 +105,17 @@ int serial8250_tx_dma(struct uart_8250_port *p)
UART_XMIT_SIZE, DMA_TO_DEVICE);
dma_async_issue_pending(dma->txchan);
-
+ if (dma->tx_err) {
+ dma->tx_err = 0;
+ if (p->ier & UART_IER_THRI) {
+ p->ier &= ~UART_IER_THRI;
+ serial_out(p, UART_IER, p->ier);
+ }
+ }
return 0;
+err:
+ dma->tx_err = 1;
+ return ret;
}
EXPORT_SYMBOL_GPL(serial8250_tx_dma);
--
2.1.0
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