linux-kernel - [PATCH] serial: 8250: 8250_omap: Do not start RX DMA on THRI interrupt

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Date:   Mon, 30 Oct 2023 19:39:51 +0100
From:   Ronald Wahl <rwahl@....de>
To:     linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Ronald Wahl <ronald.wahl@...itan.com>
Subject: [PATCH] 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 90b8596ac460 ("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.

Signed-off-by: Ronald Wahl <ronald.wahl@...itan.com>
---
 drivers/tty/serial/8250/8250_omap.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index c7ab2963040b..f2f59ec6b50b 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -1282,10 +1282,11 @@ 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) {
--
2.41.0