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

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>

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index cb51be55989eca88f8ec96c1529e7b86fa16a6ad..2292a4202425638dc84839eccb2011381a2182fe 100644 (file)
--- 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 2713664cea4ead4d77438d9151b60c2eea12ed61..f0f31d28b2f53fcce501889d356c4f55747719c3 100644 (file)
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -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);

diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index 148ffe4c232f6bd8322d3387d41f227d5d811263..69e54abb6e7174df24adec69c99b5e877c4b136c 100644 (file)
--- 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);