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.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250_core.c | 2 +-
drivers/tty/serial/8250/8250_dma.c | 30 +++++++++++++++++++++++++-----
include/linux/serial_8250.h | 1 +
3 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index ab003b6..7498ce1 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -1600,7 +1600,7 @@ 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_tx_err) && (status & UART_LSR_THRE))
serial8250_tx_chars(up);
spin_unlock_irqrestore(&port->lock, flags);
diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index 148ffe4..5c59b15 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) {
+ p->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 (p->dma_tx_err) {
+ p->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:
+ p->dma_tx_err = 1;
+ return ret;
}
EXPORT_SYMBOL_GPL(serial8250_tx_dma);
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index b161eee..02e82dc 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -85,6 +85,7 @@ struct uart_8250_port {
unsigned char mcr_force; /* mask of forced bits */
unsigned char cur_iotype; /* Running I/O type */
unsigned char rpm_tx_active;
+ unsigned char dma_tx_err;
/*
* Some bits in registers are cleared on a read, so they must
--
2.0.1
--
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