This is a note to let you know that I've just added the patch titled serial: 8250_fsl: Don't report FE, PE and OE twice to the 5.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: serial-8250_fsl-don-t-report-fe-pe-and-oe-twice.patch and it can be found in the queue-5.18 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit e32a7a0aeb979a39b67647909604c46b7bb98ec2 Author: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> Date: Mon Jul 4 10:51:19 2022 +0200 serial: 8250_fsl: Don't report FE, PE and OE twice [ Upstream commit 9d3aaceb73acadf134596a2f8db9c451c1332d3d ] 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@xxxxxxxxxxxxxxx> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220704085119.55900-1-u.kleine-koenig@xxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c index 9c01c531349d..71ce43685797 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);