FAILED: patch "[PATCH] serial: 8250: Flush DMA Rx on RLSI" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Possible dependencies:

1980860e0c82 ("serial: 8250: Flush DMA Rx on RLSI")
a931237cbea2 ("serial: 8250: Fall back to non-DMA Rx if IIR_RDI occurs") df561f6688fe ("treewide: Use fallthrough pseudo-keyword")
37711e5e2325 ("Merge tag 'nfs-for-5.9-1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1980860e0c8299316cddaf0992dd9e1258ec9d88 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <[email protected]>
Date: Tue, 8 Nov 2022 14:19:52 +0200
Subject: [PATCH] serial: 8250: Flush DMA Rx on RLSI
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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Returning true from handle_rx_dma() without flushing DMA first creates a data ordering hazard. If DMA Rx has handled any character at the point when RLSI occurs, the non-DMA path handles any pending characters jumping them ahead of those characters that are pending under DMA.

index 92dd18716169..388172289627 100644
@@ -1901,10 +1901,9 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
 		if (!up->dma->rx_running)
 			break;
 		fallthrough;
+	case UART_IIR_RLSI:
 	case UART_IIR_RX_TIMEOUT:
 		serial8250_rx_dma_flush(up);
-		fallthrough;
-	case UART_IIR_RLSI:
 		return true;
 	}
 	return up->dma->rx_dma(up);