patch "serial: 8250: Fall back to non-DMA Rx if IIR_RDI occurs" added to tty-linus

This is a note to let you know that I've just added the patch titled

serial: 8250: Fall back to non-DMA Rx if IIR_RDI occurs

to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From a931237cbea256aff13bb403da13a97b2d1605d9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <[email protected]>
Date: Tue, 8 Nov 2022 14:19:49 +0200
Subject: serial: 8250: Fall back to non-DMA Rx if IIR_RDI occurs
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DW UART sometimes triggers IIR_RDI during DMA Rx when IIR_RX_TIMEOUT should have been triggered instead. Since IIR_RDI has higher priority than IIR_RX_TIMEOUT, this causes the Rx to hang into interrupt loop. The problem seems to occur at least with some combinations of small-sized transfers (I've reproduced the problem on Elkhart Lake PSE UARTs).

If there's already an on-going Rx DMA and IIR_RDI triggers, fall graciously back to non-DMA Rx. That is, behave as if IIR_RX_TIMEOUT had occurred.

8250_omap already considers IIR_RDI similar to this change so its nothing unheard of.

---
 drivers/tty/serial/8250/8250_port.c | 4 ++++
 1 file changed, 4 insertions(+)

index fe8662cd9402..92dd18716169 100644
@@ -1897,6 +1897,10 @@ EXPORT_SYMBOL_GPL(serial8250_modem_status);
 static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
 {
 	switch (iir & 0x3f) {
+	case UART_IIR_RDI:
+		if (!up->dma->rx_running)
+			break;
+		fallthrough;
 	case UART_IIR_RX_TIMEOUT:
 		serial8250_rx_dma_flush(up);
 		fallthrough;

2.38.1