serial: 8250: 8250_omap: Do not start RX DMA on THRI interrupt

Starting RX DMA on THRI interrupt is too early because TX may not have
finished yet.

This change is inspired by commit 90b8596 ("serial: 8250: Prevent
starting up DMA Rx on THRI interrupt") and fixes DMA issues I had with
an AM62 SoC that is using the 8250 OMAP variant.

Cc: [email protected]
Fixes: c26389f ("serial: 8250: 8250_omap: Add DMA support for UARTs on K3 SoCs")
Signed-off-by: Ronald Wahl <[email protected]>
Reviewed-by: Vignesh Raghavendra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: tanstafel

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

@@ -1298,10 +1298,12 @@ static int omap_8250_dma_handle_irq(struct uart_port *port)
 
 	status = serial_port_in(port, UART_LSR);
 
-	if (priv->habit & UART_HAS_EFR2)
-		am654_8250_handle_rx_dma(up, iir, status);
-	else
-		status = omap_8250_handle_rx_dma(up, iir, status);
+	if ((iir & 0x3f) != UART_IIR_THRI) {
+		if (priv->habit & UART_HAS_EFR2)
+			am654_8250_handle_rx_dma(up, iir, status);
+		else
+			status = omap_8250_handle_rx_dma(up, iir, status);
+	}
 
 	serial8250_modem_status(up);
 	if (status & UART_LSR_THRE && up->dma->tx_err) {