tty: serial: 8250_omap: add custom DMA-RX callback

The omap needs a DMA request pending right away. If it is
enqueued once the bytes are in the FIFO then nothing will happen
and the FIFO will be later purged via RX-timeout interrupt.
This patch enqueues RX-DMA request on completion but not if it
was aborted on error. The first enqueue will happen in the driver
in startup.
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>

drivers/tty/serial/8250/8250_omap.c

@@ -619,6 +619,102 @@ static void omap_8250_unthrottle(struct uart_port *port)
 }
 
 #ifdef CONFIG_SERIAL_8250_DMA
+static int omap_8250_rx_dma(struct uart_8250_port *p, unsigned int iir);
+
+static void __dma_rx_do_complete(struct uart_8250_port *p, bool error)
+{
+	struct uart_8250_dma    *dma = p->dma;
+	struct tty_port         *tty_port = &p->port.state->port;
+	struct dma_tx_state     state;
+	int                     count;
+
+	dma_sync_single_for_cpu(dma->rxchan->device->dev, dma->rx_addr,
+				dma->rx_size, DMA_FROM_DEVICE);
+
+	dma->rx_running = 0;
+	dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state);
+	dmaengine_terminate_all(dma->rxchan);
+
+	count = dma->rx_size - state.residue;
+
+	tty_insert_flip_string(tty_port, dma->rx_buf, count);
+	p->port.icount.rx += count;
+	if (!error)
+		omap_8250_rx_dma(p, 0);
+
+	tty_flip_buffer_push(tty_port);
+}
+
+static void __dma_rx_complete(void *param)
+{
+	__dma_rx_do_complete(param, false);
+}
+
+static int omap_8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
+{
+	struct uart_8250_dma            *dma = p->dma;
+	struct dma_async_tx_descriptor  *desc;
+
+	switch (iir & 0x3f) {
+	case UART_IIR_RLSI:
+		/* 8250_core handles errors and break interrupts */
+		if (dma->rx_running) {
+			dmaengine_pause(dma->rxchan);
+			__dma_rx_do_complete(p, true);
+		}
+		return -EIO;
+	case UART_IIR_RX_TIMEOUT:
+		/*
+		 * If RCVR FIFO trigger level was not reached, complete the
+		 * transfer and let 8250_core copy the remaining data.
+		 */
+		if (dma->rx_running) {
+			dmaengine_pause(dma->rxchan);
+			__dma_rx_do_complete(p, true);
+		}
+		return -ETIMEDOUT;
+	case UART_IIR_RDI:
+		/*
+		 * The OMAP UART is a special BEAST. If we receive RDI we _have_
+		 * a DMA transfer programmed but it didn't work. One reason is
+		 * that we were too slow and there were too many bytes in the
+		 * FIFO, the UART counted wrong and never kicked the DMA engine
+		 * to do anything. That means once we receive RDI on OMAP then
+		 * the DMA won't do anything soon so we have to cancel the DMA
+		 * transfer and purge the FIFO manually.
+		 */
+		if (dma->rx_running) {
+			dmaengine_pause(dma->rxchan);
+			__dma_rx_do_complete(p, true);
+		}
+		return -ETIMEDOUT;
+
+	default:
+		break;
+	}
+
+	if (dma->rx_running)
+		return 0;
+
+	desc = dmaengine_prep_slave_single(dma->rxchan, dma->rx_addr,
+					   dma->rx_size, DMA_DEV_TO_MEM,
+					   DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+	if (!desc)
+		return -EBUSY;
+
+	dma->rx_running = 1;
+	desc->callback = __dma_rx_complete;
+	desc->callback_param = p;
+
+	dma->rx_cookie = dmaengine_submit(desc);
+
+	dma_sync_single_for_device(dma->rxchan->device->dev, dma->rx_addr,
+				   dma->rx_size, DMA_FROM_DEVICE);
+
+	dma_async_issue_pending(dma->rxchan);
+	return 0;
+}
+
 static int omap_8250_tx_dma(struct uart_8250_port *p);
 
 static void omap_8250_dma_tx_complete(void *param)