From 9d3aaceb73acadf134596a2f8db9c451c1332d3d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
Date: Mon, 4 Jul 2022 10:51:19 +0200
Subject: [PATCH] serial: 8250_fsl: Don't report FE, PE and OE twice
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Git-commit: 9d3aaceb73acadf134596a2f8db9c451c1332d3d
Patch-mainline: v6.0-rc1
References: git-fixes
Some Freescale 8250 implementations have the problem that a single long
break results in one irq per character frame time. The code in
fsl8250_handle_irq() that is supposed to handle that uses the BI bit in
lsr_saved_flags to detect such a situation and then skip the second
received character. However it also stores other error bits and so after
a single frame error the character received in the next irq handling is
passed to the upper layer with a frame error, too.
So after a spike on the data line (which is correctly recognized as a
frame error) the following valid character is thrown away, because the
driver reports a frame error for that one, too.
To weaken this problem restrict saving LSR to only the BI bit.
Note however that the handling is still broken:
- lsr_saved_flags is updated using orig_lsr which is the LSR content
for the first received char, but there might be more in the FIFO, so
a character is thrown away that is received later and not necessarily
the one following the break.
- The doubled break might be the 2nd and 3rd char in the FIFO, so the
workaround doesn't catch these, because serial8250_rx_chars() doesn't
handle the workaround.
- lsr_saved_flags might have set UART_LSR_BI at the entry of
fsl8250_handle_irq() which doesn't originate from
fsl8250_handle_irq()'s "up->lsr_saved_flags |= orig_lsr &
UART_LSR_BI;" but from e.g. from serial8250_tx_empty().
- For a long or a short break this isn't about two characters, but more
or only a single one.
Fixes: 9deaa53ac7fa ("serial: add irq handler for Freescale 16550 errata.")
Acked-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220704085119.55900-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/tty/serial/8250/8250_fsl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c
index fd4005fcd0d6..8aad15622a2e 100644
--- a/drivers/tty/serial/8250/8250_fsl.c
+++ b/drivers/tty/serial/8250/8250_fsl.c
@@ -77,7 +77,7 @@ int fsl8250_handle_irq(struct uart_port *port)
if ((lsr & UART_LSR_THRE) && (up->ier & UART_IER_THRI))
serial8250_tx_chars(up);
- up->lsr_saved_flags = orig_lsr;
+ up->lsr_saved_flags |= orig_lsr & UART_LSR_BI;
uart_unlock_and_check_sysrq_irqrestore(&up->port, flags);
--
2.35.3