linux-kernel - [PATCH 2/2] tty: serial: 8250_omap: use two-entry sg list for tx dma

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Message-ID: <20250506150748.3162-2-mans@mansr.com>
Date: Tue,  6 May 2025 16:07:30 +0100
From: Mans Rullgard <mans@...sr.com>
To: jirislaby@...nel.org
Cc: gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	linux-omap@...r.kernel.org
Subject: [PATCH 2/2] tty: serial: 8250_omap: use two-entry sg list for tx dma

On buffer wraparound, two sg entries are needed to transfer the full
contents of the kfifo.

This is equivalent to the change made to the 8250_dma driver in commit
59449c9dbdaa ("tty: serial: 8250_dma: use sgl with 2 nents to take care
of buffer wrap").

Signed-off-by: Mans Rullgard <mans@...sr.com>
---
 drivers/tty/serial/8250/8250_omap.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 180466e09605..66ba43a20725 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -1152,9 +1152,11 @@ static int omap_8250_tx_dma(struct uart_8250_port *p)
 	struct omap8250_priv		*priv = p->port.private_data;
 	struct tty_port			*tport = &p->port.state->port;
 	struct dma_async_tx_descriptor	*desc;
-	struct scatterlist sg;
+	struct scatterlist *sg;
+	struct scatterlist sgl[2];
 	int skip_byte = -1;
 	int ret;
+	int i;
 
 	if (dma->tx_running)
 		return 0;
@@ -1208,18 +1210,22 @@ static int omap_8250_tx_dma(struct uart_8250_port *p)
 		skip_byte = c;
 	}
 
-	sg_init_table(&sg, 1);
-	kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1,
-				     UART_XMIT_SIZE, dma->tx_addr);
+	sg_init_table(sgl, ARRAY_SIZE(sgl));
+	ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, sgl, ARRAY_SIZE(sgl),
+					   UART_XMIT_SIZE, dma->tx_addr);
 
-	desc = dmaengine_prep_slave_sg(dma->txchan, &sg, 1, DMA_MEM_TO_DEV,
+	desc = dmaengine_prep_slave_sg(dma->txchan, sgl, ret, DMA_MEM_TO_DEV,
 			DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 	if (!desc) {
 		ret = -EBUSY;
 		goto err;
 	}
 
-	dma->tx_size = sg_dma_len(&sg);
+	dma->tx_size = 0;
+
+	for_each_sg(sgl, sg, ret, i)
+		dma->tx_size += sg_dma_len(sg);
+
 	dma->tx_running = 1;
 
 	desc->callback = omap_8250_dma_tx_complete;
-- 
2.49.0