8250_mid: arm rx dma on all ports with dma continously

Instead of initiating rx dma when the first char arrives in the UART, arm rx dma
continously. Dma transfers automatically empty rx fifo, preventing overruns. As
before, transfer terminates when the dma buffer is full or when a 4 char
interchar gap is received (timeout). After timeout we arm immediately the dma again.

Signed-off-by: Ferry Toth <ftoth@exalondelft.nl>

drivers/tty/serial/8250/8250_mid.c

@@ -88,6 +88,8 @@ static int tng_handle_irq(struct uart_port *p)
  err = hsu_dma_get_status(chip, mid->dma_index * 2 + 1, &status);
  if (err > 0) {
  serial8250_rx_dma_flush(up);
+ /* immediately after flushing arm dma again */
+ if (up->dma) up->dma->rx_dma(up);
  ret |= 1;
  } else if (err == 0)
  ret |= hsu_dma_do_irq(chip, mid->dma_index * 2 + 1, status);
@@ -232,6 +234,34 @@ static void mid8250_set_termios(struct uart_port *p,
  serial8250_do_set_termios(p, termios, old);
 }
 
+static int mid8250_startup(struct uart_port *port)
+{
+ struct uart_8250_port *up = up_to_u8250p(port);
+ struct mid8250 *mid = port->private_data;
+ int ret;
+
+ ret = serial8250_do_startup(port);
+
+ /* arm rx dma at do_startup time
+ * register new do_startup and do_shutdown
+ * in mid8250_probe
+ */
+
+ if (up->dma) up->dma->rx_dma(up);
+
+ return ret;
+}
+
+static void mid8250_shutdown(struct uart_port *port)
+{
+ struct uart_8250_port *up = up_to_u8250p(port);
+ struct mid8250 *mid = port->private_data;
+
+ if (up->dma) serial8250_rx_dma_flush(up);
+
+ serial8250_do_shutdown(port);
+}
+
 static bool mid8250_dma_filter(struct dma_chan *chan, void *param)
 {
  struct hsu_dma_slave *s = param;
@@ -306,6 +336,8 @@ static int mid8250_probe(struct pci_dev *pdev, const struct pci_device_id *id)
  uart.port.uartclk = mid->board->base_baud * 16;
  uart.port.flags = UPF_SHARE_IRQ | UPF_FIXED_PORT | UPF_FIXED_TYPE;
  uart.port.set_termios = mid8250_set_termios;
+ uart.port.startup = mid8250_startup;
+ uart.port.shutdown = mid8250_shutdown;
 
  uart.port.mapbase = pci_resource_start(pdev, bar);
  uart.port.membase = pcim_iomap(pdev, bar, 0);