FAILED: patch "[PATCH] serial: 8250: Store to lsr_save_flags after lsr read" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-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]>.

thanks,

greg k-h

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

From be03b0651ffd8bab69dfd574c6818b446c0753ce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <[email protected]>
Date: Fri, 20 May 2022 13:35:41 +0300
Subject: [PATCH] serial: 8250: Store to lsr_save_flags after lsr read
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Not all LSR register flags are preserved across reads. Therefore, LSR readers must store the non-preserved bits into lsr_save_flags.

This fix was initially mixed into feature commit f6f586102add ("serial:
8250: Handle UART without interrupt on TEMT using em485"). However, that feature change had a flaw and it was reverted to make room for simpler approach providing the same feature. The embedded fix got reverted with the feature change.

Re-add the lsr_save_flags fix and properly mark it's a fix.

index 78b6dedc43e6..8f32fe9e149e 100644
@@ -1517,6 +1517,8 @@ static inline void __stop_tx(struct uart_8250_port *p)
 		unsigned char lsr = serial_in(p, UART_LSR);
 		u64 stop_delay = 0;
 
+		p->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
+
 		if (!(lsr & UART_LSR_THRE))
 			return;
 		/*