linux-kernel - [PATCH v4] serial: 8250: 8250_omap: Do not start RX DMA on THRI interrupt

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Date:   Wed,  1 Nov 2023 18:14:31 +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>, stable@...r.kernel.org
Subject: [PATCH v4] serial: 8250: 8250_omap: Do not start RX DMA on THRI interrupt

From: Ronald Wahl <ronald.wahl@...itan.com>

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.

Cc: stable@...r.kernel.org
Fixes: c26389f998a8 ("serial: 8250: 8250_omap: Add DMA support for UARTs on K3 SoCs")
Signed-off-by: Ronald Wahl <ronald.wahl@...itan.com>
---
V4: - add missing braces to fix build warning

V3: - add Cc: stable@...r.kernel.org

V2: - add Fixes: tag
    - fix author

 drivers/tty/serial/8250/8250_omap.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index c7ab2963040b..1122f37fe744 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -1282,10 +1282,12 @@ 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) {
--
2.41.0