This is a note to let you know that I've just added the patch titled
Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed
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-testing 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 be merged to the tty-next branch sometime soon,
after it passes testing, and the merge window is open.
If you have any questions about this process, please let me know.
>From d02b006b29de14968ba4afa998bede0d55469e29 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@xxxxxxxxxx>
Date: Thu, 7 Oct 2021 15:31:46 +0200
Subject: Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed
field"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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This reverts commit 32262e2e429cdb31f9e957e997d53458762931b7.
The commit in question claims to determine the inverse of
serial8250_get_divisor() but failed to notice that some drivers override
the default implementation using a get_divisor() callback.
This means that the computed line-speed values can be completely wrong
and results in regular TCSETS requests failing (the incorrect values
would also be passed to any overridden set_divisor() callback).
Similarly, it also failed to honour the old (deprecated) ASYNC_SPD_FLAGS
and would break applications relying on those when re-encoding the
actual line speed.
There are also at least two quirks, UART_BUG_QUOT and an OMAP1510
workaround, which were happily ignored and that are now broken.
Finally, even if the offending commit were to be implemented correctly,
this is a new feature and not something which should be backported to
stable.
Cc: Pali Rohár <pali@xxxxxxxxxx>
Fixes: 32262e2e429c ("serial: 8250: Fix reporting real baudrate value in c_ospeed field")
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20211007133146.28949-1-johan@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250_port.c | 17 -----------------
1 file changed, 17 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index dc6900b2daa8..66374704747e 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2584,19 +2584,6 @@ static unsigned int serial8250_get_divisor(struct uart_port *port,
return serial8250_do_get_divisor(port, baud, frac);
}
-static unsigned int serial8250_compute_baud_rate(struct uart_port *port,
- unsigned int quot)
-{
- if ((port->flags & UPF_MAGIC_MULTIPLIER) && quot == 0x8001)
- return port->uartclk / 4;
- else if ((port->flags & UPF_MAGIC_MULTIPLIER) && quot == 0x8002)
- return port->uartclk / 8;
- else if (port->type == PORT_NPCM)
- return DIV_ROUND_CLOSEST(port->uartclk - 2 * (quot + 2), 16 * (quot + 2));
- else
- return DIV_ROUND_CLOSEST(port->uartclk, 16 * quot);
-}
-
static unsigned char serial8250_compute_lcr(struct uart_8250_port *up,
tcflag_t c_cflag)
{
@@ -2727,14 +2714,11 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk)
baud = serial8250_get_baud_rate(port, termios, NULL);
quot = serial8250_get_divisor(port, baud, &frac);
- baud = serial8250_compute_baud_rate(port, quot);
serial8250_rpm_get(up);
spin_lock_irqsave(&port->lock, flags);
uart_update_timeout(port, termios->c_cflag, baud);
- if (tty_termios_baud_rate(termios))
- tty_termios_encode_baud_rate(termios, baud, baud);
serial8250_set_divisor(port, baud, quot, frac);
serial_port_out(port, UART_LCR, up->lcr);
@@ -2766,7 +2750,6 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
baud = serial8250_get_baud_rate(port, termios, old);
quot = serial8250_get_divisor(port, baud, &frac);
- baud = serial8250_compute_baud_rate(port, quot);
/*
* Ok, we're now changing the port state. Do it with
--
2.33.0
