tty: serial: sh-sci: Add RZ/G2L SCIFA DMA tx support

SCIFA IP on RZ/G2L SoC has the same signal for both interrupt
and DMA transfer request. Setting DMARS register for DMA transfer
makes the signal to work as a DMA transfer request signal and
subsequent interrupt requests to the interrupt controller
are masked. Similarly clearing DMARS register makes signal to work as
interrupt signal and subsequent interrupt requests to the interrupt
controller are unmasked.

Add SCIFA DMA tx support for RZ/G2L alike SoCs by disabling TXI line
interrupt and setting DMARS registers by DMA api for DMA transfer request.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20230412145053.114847-2-biju.das.jz@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -588,12 +588,17 @@ static void sci_start_tx(struct uart_port *port)
 
 	if (s->chan_tx && !uart_circ_empty(&s->port.state->xmit) &&
 	    dma_submit_error(s->cookie_tx)) {
+		if (s->cfg->regtype == SCIx_RZ_SCIFA_REGTYPE)
+			/* Switch irq from SCIF to DMA */
+			disable_irq(s->irqs[SCIx_TXI_IRQ]);
+
 		s->cookie_tx = 0;
 		schedule_work(&s->work_tx);
 	}
 #endif
 
-	if (!s->chan_tx || port->type == PORT_SCIFA || port->type == PORT_SCIFB) {
+	if (!s->chan_tx || s->cfg->regtype == SCIx_RZ_SCIFA_REGTYPE ||
+	    port->type == PORT_SCIFA || port->type == PORT_SCIFB) {
 		/* Set TIE (Transmit Interrupt Enable) bit in SCSCR */
 		ctrl = serial_port_in(port, SCSCR);
 		serial_port_out(port, SCSCR, ctrl | SCSCR_TIE);
@@ -1192,9 +1197,15 @@ static void sci_dma_tx_complete(void *arg)
 		schedule_work(&s->work_tx);
 	} else {
 		s->cookie_tx = -EINVAL;
-		if (port->type == PORT_SCIFA || port->type == PORT_SCIFB) {
+		if (port->type == PORT_SCIFA || port->type == PORT_SCIFB ||
+		    s->cfg->regtype == SCIx_RZ_SCIFA_REGTYPE) {
 			u16 ctrl = serial_port_in(port, SCSCR);
 			serial_port_out(port, SCSCR, ctrl & ~SCSCR_TIE);
+			if (s->cfg->regtype == SCIx_RZ_SCIFA_REGTYPE) {
+				/* Switch irq from DMA to SCIF */
+				dmaengine_pause(s->chan_tx_saved);
+				enable_irq(s->irqs[SCIx_TXI_IRQ]);
+			}
 		}
 	}