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tty: serial: 8250_dma: handle error on TX submit

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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@atomide.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sebastian Andrzej Siewior 2014-09-29 20:06:40 +02:00 committed by Greg Kroah-Hartman
parent 61929cf016
commit b220282156
3 changed files with 28 additions and 6 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
drivers/tty/serial/8250/8250.h
View file

@ -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 {

3
drivers/tty/serial/8250/8250_core.c
View file

@ -1597,7 +1597,8 @@ 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);

30
drivers/tty/serial/8250/8250_dma.c
View file

@ -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);